Dairy, Science, Society, and the Environment
Summary and Keywords
Dairy has intertwined with human society since the beginning of civilization. It evolves from art in ancient society to science in the modern world. Its roles in nutrition and health are underscored by the continuous increase in global consumption. Milk production increased by almost 50% in just the past quarter century alone. Population growth, income rise, nutritional awareness, and science and technology advancement contributed to a continuous trend of increased milk production and consumption globally. With a fourfold increase in milk production per cow since the 1940s, the contemporary dairy industry produces more milk with fewer cows, and consumes less feed and water per liter of milk produced. The dairy sector is diversified, as people from a wider geographical distribution are consuming milk, from cattle to species such as buffalo, goat, sheep, and camel. The dairy industry continues to experience structural changes that impact society, economy, and environment. Organic dairy emerged in the 1990s as consumers increasingly began viewing it as an appropriate way of both farming and rural living. Animal welfare, environmental preservation, product safety, and health benefit are important considerations in consuming and producing organic dairy products. Large dairy operations have encountered many environmental issues related to elevated greenhouse gas emissions. Dairy cattle are second only to beef cattle as the largest livestock contributors in methane emission. Disparity in greenhouse gas emissions per dairy animal among geographical regions can be attributed to production efficiency. Although a number of scientific advancements have implications in the inhibition of methanogenesis, improvements in production efficiency through feeding, nutrition, genetic selection, and management remain promising for the mitigation of greenhouse gas emissions from dairy animals. This article describes the trends in milk production and consumption, the debates over the role of milk in human nutrition, the global outlook of organic dairy, the abatement of greenhouse gas emissions from dairy animals, as well as scientific and technological developments in nutrition, genetics, reproduction, and management in the dairy sector.
Dairy and the Society
Milk has been entangled with evolution of human civilization from perhaps as early as 10,000 to 8,000 bc, when aurochs, the wild ancestors of modern cows, were domesticated. The production and consumption of milk, cheese, and even ice cream can be traced back centuries. Fermented milk products have been produced since around 10,000 bc, and ice cream, in a form of frozen milk and rice, was found in China in 200 bc. Milk was exploited from the beginning of the middle Pre-Pottery Neolithic B (PPNB) in the Near East based on the unambiguous evidence of certain overall culling profiles of goats and sheep (Helmer, Gourichon, & Vila, 2007). Isotopic analysis of pottery residues has allowed the differentiation of meat fat and dairy fats (Evershed, Payne, Sherratt, Copley, Coolidge, & Urem-Kotsu, 2008) and has indicated that milk was being utilized as early as the Neolithic. A wide range of dairy products were utilized in early societies of India and Ireland, and consumption was apparently confined to raw milk in Egypt (McCormick, 2012). Milk and dairy products played important roles in early religious practices, and the differences in the range of dairy products consumed among different societies imply that dairying technology was not applied to its full potential.
Dairy was more of an art than science until the 19th century, when pasteurization, condensed milk, the continuous centrifugal cream separator, automatic bottle filler and capper, tuberculin testing of dairy herds, the Babcock test for milk-fat content, commercial pasteurizing machines, and the milking machine with intermittent pulsation were developed and introduced.
Dairy and the Environment
Dairy farming continues to evolve as the consumption of milk and dairy products continues to increase. Globally, the production per cow increases as the total number of cows decreases. This results in a substantial increase in production efficiency, requiring less feed, water, and environmental cost per unit of milk produced. As the benefits of this efficiency become clear in the economic returns, the size of dairy operations increases, and large commercial dairies become more prevalent. Concerns about environmental consequences grow, with greenhouse gas emissions and animal-waste disposal as the main focal points. Although milk and dairy products are common food items in modern society, consumers have become increasingly sophisticated. Concerned not only with nutrition and product safety, consumers are also increasingly demanding production systems that are compatible with animal welfare standards and environmental sustainability. Organic dairy emerged as an alternative to conventional dairy and is growing rapidly.
Among the wide range of issues associated with dairy are milk production, consumption, and the role of milk and dairy products in human health and nutrition. As the dairy industry continues to evolve, restructuring and the consolidation of operations has an impact on society. Addressing the environmental issues associated with dairy is vital for a sustainable growth and continuing acceptance by consumers. Greenhouse gas emissions by the dairy, mitigation of enteric methanogenesis in dairy ruminants, and management of dairy waste systems are important subjects that may well define the future of the dairy industry. Understanding the past and present will shape the future of the dairy sector.
Milk Production and Consumption
Trends in Milk Production
Global milk production reached 768 million tonnes in 2013, a 45% increase in two decades (Food and Agriculture Organization [FAO], 2016a). Population growth, increased incomes, nutritional awareness, and science and technology advancement contributed to a continuous trend of increase in milk production globally (Thornton, 2010). The leading milk-producing countries in 2013 were India, the Unites States, China, and Pakistan (FAO, 2016a). In addition to India and the United States, Russia, Germany, and France were among the top-producing countries a decade earlier (2003). The largest increase in milk production during the past decade (2003–2013) was in India. Asia (36%), Europe (30%), and Americas (24%) produced more than 90% of the milk in the world in 2013 (FAO, 2016a). A decade earlier in 2003 Europe was the top-producing region, contributing close to 40% of the total world output of milk.
Although India is the leading milk-producing country, small operations are predominant, often with one or two cows. The income generated from milk production by these small holders is often secondary. There is an interest in both the public and private sectors in modernizing the dairy sector. Dairy cooperatives in India have been reported to be effective in addressing fair pricing for both consumers and producers and in quality of products through storage and marketing (Shah, 2012). With apparent benefits, the cooperatives face a number of challenges, such as real estate price increases, declining rates of return, and labor shortages (Shah, 2012). Sahiwal, Devni, and Giri are the major Indian dairy cow breeds, and India’s dairy farmers have also introduced breeds such as Holstein, Jersey, and Karen Swiss.
Milk production in the United States is characterized by larger herd sizes in the western region as compared to Midwestern and eastern regions. Although the milk production increased by 16% during 2005–2014, the number of operations decreased by 33% during 2003–2012 (United States Department of Agriculture [USDA], 2016a). There were slightly fewer than 60,000 dairy operations in 2012; 85% of these operations had fewer than 100 cows, and 3.3% had more than 500 cows. Milk production is influenced by season. Peak milk production occurs from March to May, when the weather, and forage supply and its nutritional value are favorable. Holstein, Brown Swiss, Guernsey, Ayrshire, Jersey, Red and White, and Milking Shorthorn are the major breeds in the United States, according to the Purebred Dairy Cattle Association (2016).
The European Union (EU) is the single largest milk-producing block of countries in the world, producing 164.8 million tonnes of milk in 2014, with 96.8% coming from cows (Eurostat, 2014). In 2014, the EU-28’s dairy herds of 23.6 million cows had an estimated average yield of 6,777 kg per head, with disparities in production averages among the member nations. Germany and France were the top-producers of cow milk in EU. Among the EU-28, Spain produced the largest quantity of milk from species other than cattle, followed by France, Greece, and Italy. Greece is the only country where milk from other species surpasses cow milk. In 2014, the dairy markets in Europe were highly specific, with the United Kingdom supplying the largest quantity (about a quarter) of drinking milk, while Germany, Italy, and the Netherlands accounted for almost three quarters of cheese produced across the EU-28 in 2014 (Eurostat, 2014). In EU-27 from 2001 to 2011 the dairy cow population decreased from 64 million to 56 million, and the average annual milk production per cow was 6,692 kg, a 20% increase in production efficiency in a decade. The EU experienced structural changes in dairy operations, with the number of operations decreasing and the number of cows per operation increasing. A milk-quota regime was introduced in 1984 to restrict milk production levels and control the high budgetary costs of managing EU dairy commodity surpluses. The quota system expired in 2015.
Milk Production Efficiency
Largely owing to advancements in science and technology and the improvement in genetic improvement and management, the efficiency of milk production (measured as milk yield per cow) continues to increase. Globally, from 1991 to 2006, the number of milk cows decreased from 133 to 125 million heads, whereas milk production increased from 377 to 418 million metric tonnes, a net increase of 18% in production efficiency during the period (USDA, 2007). In the United States, milk production per cow per year increased 14% just in the past decade, from 8,863 to 10,114 kg (USDA, 2016a). There were 9.6 million milking cows in the 1870s in the United States. The number of milking cows peaked in the 1940s to just below 25 million, followed by a continuous decline to just over 9 million in 2007 (USDA, 2007). Rolling herd average milk production for all herds in the United States increased from 7,969 kg in 1991 to 9,765 kg in 2007, representing an approximate increase of 1,796 kg, or 22.5%. On the other hand, production efficiency increased by 20% during 2001–2011 in the EU-28. Figure 1 depicts the historical dairy herd and milk production in the United States.
To compare production efficiency between 1994 and 2007, a model based on the metabolism and nutrient requirements of the dairy herd was used to estimate resource inputs and waste outputs of milk production (Capper, Cady, & Bauman, 2009). The authors concluded that there was a fourfold increase in milk production per cow during the period, with the contemporary dairy industry producing 59% more milk from 64% fewer cows that consumed 77% less feed and 65% less water per liter of milk produced compared to dairy production in 1944 (Capper et al., 2009). This tremendous increase in production efficiency was also documented, and several factors affecting the sustainability of the U.S. dairy industry, including climate change, rapid scientific and technological innovation, globalization, integration of societal values, and multidisciplinary research initiatives were identified (von Keyserlingk, Martin, Kebreab, Knowlton, Grant, Stephenson et al., 2013).
Milk from Novel Species
Consumers are increasingly aware of milk from species other than cattle, notably buffalo, goats, sheep, and camels. Buffalo milk production increased from 48 million metric tonnes in 1993 to over 102 million metric tonnes in 2013 (FAO, 2016b). More than 96% of buffalo milk is produced in Asia, with India and Pakistan being the leading producing countries. The major buffalo breeds are Murrah, Bahadawari, Surti, Nili-Ravi, and Mehashana. Buffalo milk is the largest milk sector in India; more than half of total milk production is from buffalos. During 1993–2013, average annual milk production was 49.4 tonnes from buffalos versus 39.8 tonnes from cows (FAO, 2016a). In general, the total solids, fats, proteins, lactose and mineral contents, and energy values are higher in buffalo milk compared to cow milk. This may largely be attributed to lower production levels in buffalos than cattle. There were claims that the presence of higher levels of various immunoglobulins, lactoferrin, lysozyme, and lactoperoxidase, as well as bifidogenic factors, rendered buffalo milk more suitable than cow milk for the preparation of a wide range of special dietary and health foods.
Milk produced by goats increased from 11 million tonnes in 1993 to just under 18 million tonnes in 2013 (FAO, 2016a). The continents of Asia (56.3%), Africa (22.5%), and Europe (17.6%) are the leaders in goat milk production. India, Bangladesh, Sudan, and France are the top-producing countries. Alpine, LaMancha, Nigerian Dwarf, Nubian, Oberhasli, Saanen, Sable, and Toggenburg are the dairy breeds recognized by the American Dairy Goat Association (American Dairy Goat Association, 2016). Goat milk has been useful in alleviating gastrointestinal disorders and allergies to cow milk because of differences in its physic-chemical characteristics (Park, Juarez, Ramos, & Haenlein, 2007). For example, caprine casein micelles contain more calcium and inorganic phosphorus, are less solvated, less heat stable, and lose β-casein more readily than bovine casein micelles. Moreover, the fat globule size in caprine casein micelles is smaller than that of cows. Goat milk is significant in human nutrition since goat milk is used to feed more starving and malnourished people in the developing parts of the world than is cow milk. Goat milk is also significant in filling the gastronomic needs of connoisseur consumers, which is growing in market share in many developed countries (Haenlein, 2004). It is important to note that both chemical composition and physical characteristics of goat milk can be influenced by factors such as nutrition, management, climate, physiological stage, and genetics (Morand-Fehr, Fedele, Decandia, & Le Frileux, 2007; Goetsch, Zeng, & Gipson, 2011)
Milk produced by sheep increased from 7.7 million tonnes in 1993 to over 10.1 million tonnes in 2013 (FAO, 2016a). Asia (44.9%), Europe (33.8%), and Africa (20.9%) are the leading continents. China, Turkey, Greece, and Italy are the top-producing countries. East Friesian, Lacaune, Awassi, and Assaf are popular dairy sheep breeds. Typically, dairy sheep breeds produced 180–500 kg milk per lactation, whereas milk production from conventional sheep breeds was only 40 kg to 80 kg per lactation.
Dairy sheep have been farmed traditionally in the Mediterranean basin in Southern, Central, and Eastern Europe, and in Near East countries. Modern breeding programs were conceived in the 1960s. A common and efficient selection scheme for local dairy sheep breeds is based on a pyramidal management of the population, in which the breeders of nucleus flocks are at the top, and where pedigree and official milk recording, artificial insemination, controlled natural mating, and breeding-value estimation are carried out to generate genetic progress (Carta, Casu, & Salaris, 2009). Genomic selection was used more recently to increase accuracy and to decrease generation intervals in Lacaune sheep (Duchemin, Colombani, Legarra, Baloche, Larroque, Astruc et al., 2012). There are important differences in physic-chemical characteristics of sheep milk compared to cow milk (Park et al., 2007). Levels of the metabolically valuable short- and medium-chain fatty acids, caproic (C6:0; 2.9%, 2.4%, 1.6% in sheep, goat, cow, respectively), caprylic (C8:0; 2.6%, 2.7%, 1.3%), capric (C10:0; 7.8%, 10.0%, 3.0%), and lauric (C12:0; 4.4%, 5.0%, 3.1%) are significantly higher in sheep and goat than in cow milk, respectively. Sheep- and goat-milk proteins are also important sources of bioactive angiotensin-converting enzyme inhibitory peptides and antihypertensive peptides. They can provide a nonimmune disease defense and control of microbial infections. Sheep milk contains higher levels of total solids and major nutrients than goat and cow milk. The average fat globule size is smallest (<3.5 μm) in sheep milk, followed by goat and cow milk, an important characteristic for digestion (Park et al., 2007).
Milk produced by camel increased from 1.4 million tonnes in 1993 to over 2.9 million tonnes in 2013 (FAO, 2016a). The largest increase occurred in 2006–2007, from 1.88 to 2.52 million tonnes. More than 91% of camel milk is produced in Africa, where Somalia and Kenya are the leading producers. Compared to human milk, camel milk contained higher fat, higher essential fatty acids, casein protein, ash, Ca, Mg, P, K, Na, Fe, Cu, Vitamin C, and niacin but was lower in whey protein, lactose, and Zn (Shamsia, 2009). Camel milk was characterized by higher immunoglobulins but lower in lysozyme and lactoferrin than human milk. It was suggested as a good food of high nutritive and therapeutic application, with potential against diarrhea-causing viruses (Shamsia, 2009). Zibaee, Hosseini, Yousefi, Taghipour, Kiani, and Noras (2015) reviewed 472 records and selected 35 studies on therapeutic characteristic of camel milk ranging from metabolic and autoimmune diseases, hepatitis, Rota viral diarrhea, tuberculosis, cancer, diabetes, liver cirrhosis, rickets, autism, to Crohn’s disease in adults; and children diseases including autism, food and milk allergies, intolerance to lactose, and diarrhea. They concluded that camel milk could be useful as a less invasive and costly supplement.
Consumption of bovine milk varies with geographical regions. The Food and Agriculture Organization of the United Nations (FAO) classified milk consumption as high (> 150 kg/capita/year) in Argentina, Armenia, Australia, Costa Rica, Europe, Israel, Kyrgyzstan, North America, and Pakistan; medium (30 kg to 150 kg/capita/year) in India, the Islamic Republic of Iran, Japan, Kenya, Mexico, Mongolia, New Zealand, North and Southern Africa, most of the Near East, and most of Latin America and the Caribbean; and low (< 30 kg/capita/year) in Vietnam, Senegal, most of Central Africa, and most of East and Southeast Asia (FAO, 2016b). Although per capita milk consumption in developing countries has increased almost twofold since the early 1960s, it was outpaced by the consumption of other livestock products with meat consumption having more than tripled and egg consumption having increased fivefold (FAO, 2016a). More than 6 billion people worldwide consume milk and milk products, and the majority of these people live in developing countries. Milk provides 3% of dietary energy supply in Asia and Africa, compared with 8% to 9% in Europe and Oceania; 6% to 7% of dietary protein supply in Asia and Africa, compared with 19% in Europe; and 6% to 8% of dietary fat supply in Asia and Africa, compared with 11% to 14% in Europe, Oceania, and the Americas (FAO, 2016b).
Consumption of total dairy products has risen faster than the growth in population (USDA, 2016b). On a milk-equivalent and milk-fat basis, annual per-capita consumption increased from 255 kg in 1996 to 279 kg in 2014–2015. However, use of individual products has shown great variation. Within two decades, total annual per-capita consumption of fluid milk has declined (92.7 kg to 72.3 kg) because of competition from other beverages and a declining share of children in the population. Growing demand for cheese has been one of the most important forces shaping the U.S. dairy industry. Rising per-capita cheese consumption (8.5 kg to 16.4 kg) has been aided by the availability of a wider variety of cheeses, more away-from-home eating, and the greater popularity of ethnic cuisines that employ cheese as a major ingredient. Per-person use of butter has increased in recent years (from 2 kg to 2.5 kg in ten years). However, use of most dry and condensed milks has declined as in-home food preparation has diminished and fresh milk has become cheaper and achieved a longer shelf life (USDA, 2016b).
Milk and Human Health
Bovine milk is considered a nutrient-rich food item because of lipids, proteins, essential amino acids, essential fatty acids, vitamins, and minerals. These nutrients are needed to support growth and development in calves and have been considered to be excellent sources of food and nutrition in humans.
Framed within epidemiologic, experimental, and biochemical evidence, effect of milk intake on a wide range of human health issues, including body-weight gain, diabetes, blood pressure, cholesterol level, metabolic syndrome, cardiovascular health, cognitive function, chemoprevention, and putative functional properties were recently reviewed (Visioli & Strata, 2014). It was concluded that milk and its derivatives are useful foods throughout all life periods, in particular during childhood and adolescence, when their calcium, protein, phosphorus, and other micronutrients may promote skeletal, muscular, and neurologic development. It appears that milk as part of a balanced diet is beneficial for human health. For some individuals, consuming excessive amounts of milk, milk proteins, fat, and milk sugar may be of health concern (Haug, Høstmark, & Harstad, 2007). However, the content of oleic acid, conjugated linoleic acid, omega-3 fatty acids, short- and medium-chain fatty acids, vitamins, minerals, and bioactive compounds may promote positive health effects. It is suggested that ingesting full-fat milk or fermented milk might be favorable for glycemic regulation because of the increased gastrointestinal transit time (Haug et al., 2007). In 2004, Dairy Management Inc. and the National Dairy Promotion and Research Board initiated a nationwide advertising campaign claiming that consuming three daily servings of milk or other dairy products could help with weight loss. However, the milk and weight loss claim was withdrawn in 2007.
Huth, DiRienzo, and Miller (2006) reviewed a large body of scientific evidence collected in recent decades focused on health benefits, including hypertension, osteoporosis, weight control and body fat, and cancer. They concluded the following: (a) an adequate intake of calcium and other nutrients from dairy foods reduces the risk of osteoporosis by increasing bone acquisition during growth, slowing age-related bone loss, and reducing osteoporotic fractures; (b) a number of animal, observational, and clinical studies have shown that dairy food consumption can help reduce the risk of hypertension, and emerging data indicate that specific peptides associated with casein and whey proteins can significantly lower blood pressure; (c) clinical studies have demonstrated that during caloric restriction, body-weight and body-fat loss occur when adequate calcium is provided by supplements and that this effect is further augmented by an equivalent amount of calcium supplied from dairy foods; and (d) several studies support a role for calcium, vitamin D, and dairy foods against colon cancer, and that conjugated linoleic acid, a fatty acid found naturally in dairy fat, confers a wide range of anticarcinogenic benefits in experimental animal models and is especially consistent for protection against breast cancer.
Bovine milk fortified with iron for infants prior to 9 to 12 month of age was recommended (Leung & Sauve, 2003). Leung and Sauve (2003) also included studies suggesting that infants’ early exposure to cow-milk proteins increased the risk of developing allergy to milk proteins and risk for type 1 diabetes mellitus. Lactose intolerance, when there is insufficient lactase in the duodenum to digest lactose, is more prevalent in the populations of African and Asian origin. It can be genetically or environmentally induced. Congenital alactasia, an autosomal recessive enzyme defect that prevents lactase expression from birth, is rare but can be fatal if a substitution of milk is not provided. Primary hypolactasia, absence of a lactase persistence allele, affects only adults. Acquired hypolactasia, also termed secondary hypolactasia, caused by an injury in small intestine is environmentally induced and thus reversible. Prolonged absence of milk consumption after weaning can result in hypolactasia but can be reversed by gradual inclusion of milk in the diet. Lactose-free dairy products are widely available and allow for milk consumption by the lactose-intolerant population.
A recent review based on the screening of more than 1,000 scientific articles (of which 81 were selected) concluded that drinking raw milk carries an increased risk of foodborne illnesses as compared to drinking pasteurized milk (Davis, Li, & Nachman, 2014). The review identified no evidence that the potential benefits of consuming raw milk outweigh the known health risks. Without underlying cause, studies detected a relationship between drinking raw milk and reduced allergies among rural children and infants (Loss, Apprich, Waser, Kneifel, Genuneit, Buchele et al., 2011; Macdonald, Brett, Kelton Majowicz, Snedeker, & Sargeant, 2011). There were reports of decreased vitamin B2, B12, and E in pasteurized milk as compared to raw milk (Lejeune & Rajala-Schultz, 2009; Macdonald et al., 2011). Lactoperoxidase, a heat-sensitive bacteriostatic enzyme, was reduced when milk was pasteurized with concentrations decreasing dramatically after higher-temperature pasteurization (Marks, Grandison, & Lewis, 2001).
Dairy Science and Technology
Dairy production, processing, and marketing in the modern world are a blend of centuries’ old knowledge of traditional milk production and processing and the application of modern science and technology. Current and recent generations of dairy producers can be credited with the evolution of dairy from art to science. The dairy production and processing sectors have benefited from advancements in science and technology and have evolved from more art and less science to a balanced blend of art and science. Modern science and technology also allow for dairy production and processing to overcome the cultural, climatic, and geographical barriers to become a global enterprise. Advancements in nutrition, genetics, and management have improved production efficiency and reduced carbon prints.
Total Mixed Ration
After its introduction in the 1950s, total mixed ration (TMR) became one of the most widely used feeding systems among dairy producers. The practice of mixing forage with concentrate, protein, mineral, and vitamin supplements, and additives allows for the steady delivery of nutrients in the animal’s system. It also facilitates a better environment for microbial fermentation in the rumen by providing a more synchronized supply of nitrogen and energy, which are needed for optimal microbial protein synthesis. It provides more balanced diets to various groups of dairy cows based on their nutritional needs at various physiological stages and production levels, a feeding program known as “phase feeding.” TMR is generally more labor-intensive and requires the chopping of forage and blending, which involves additional expenditures for equipment and maintenance. Although it reduces the selection by the animal, TMR requires the careful analysis of the nutrient content of various ingredients to ensure deliver a balanced diet in accordance to nutrient requirements of animals. The TMR is adopted mostly by intensive systems with larger herds, but it is also used in combination with pasture or extensive feeding. Dairy cows fed with TMR produced more milk with higher feed intake than those on pasture supplemented with concentrate or on pasture supplemented with TMR (Bargo, Muller, Delahoy, & Cassidy, 2002).
Recombinant Bovine Somatotropin
A number of studies of recombinant bovine somatotropin (rbST) conducted in the late 1970s and 1980s demonstrated an increase in milk production in dairy cows. The synthetic hormone was manufactured using genetic engineering technology by cloning the bST gene into Escherichia coli. After the bacteria were grown in bioreactors, the rbST was then harvested through separation. The synthetic form of rbST works similarly to natural occurring bovine growth hormone to slow down the natural decrease in mammary cells that occurs after peak lactation. Although rbST is effective in increasing milk production, it is not without controversies. Most of the discussion was on animal welfare, human health, and labeling. A meta-analysis based on 86 reports that were selected from 1,777 articles and 26 submitted study reports concluded that rbST increases average daily milk by 3.0 kg (11.3%) in primiparous Holsteins and 4.3 kg (15.6%) in multiparous Holsteins, with the average dry matter intake increasing by 1.5 kg/d (Dohoo, Leslie, Descôteaux, Fredeen, Dowling, Preston et al., 2003a). Treating cows with rbST increases the risk of clinical mastitis and lameness and may reduce fertility with a possible benefit of reducing metabolic disorder (Dohoo, Descôteaux, Leslie, Fredeen, Shewfelt, Preston et al., 2003b). The claims that human consumption of milk from cows treated with rbST is unsafe are either unsubstantiated or inconclusive. The use of rbST does not increase risk for type 1 and type 2 diabetes in children and adults consuming milk and dairy products; nor does it increase insulin-like growth factor–I outside the typical range for milk concentration (Collier & Bauman, 2014). After more than 20 years of commercial use of rbST in the United States, it was concluded that rbST is a technology that allows feed resources to be used more efficiently with less animal waste and a reduced carbon footprint (Collier & Bauman, 2014). However, rbST has not been approved for use in the European Union, Japan, Canada, Australia, New Zealand, Israel, and Argentina, largely on the grounds of animal welfare.
Robotic Milkers, Automatic Feeders, and Sensors
Reduced labor, a better social life for dairy-farm families, and increased milk yields due to more frequent milking are generally recognized as important benefits of automatic milking systems (AMSs) using robotic milkers (Figure 2).
These have been available since the 1990s, and their popularity continues to increase. Perhaps no other new technology since the introduction of the milking machine has attracted so much interest among dairy farmers and the periphery. Robotic milking increases flexibility so that family farmers can be away occasionally. The system allows each cow to move at her own pace and to approach the AMS to get milked when she is ready. It also provides milk producers with data on such issues as udder health and milk efficiency. Some in-line parlor technologies monitor and evaluate many different facets of the production system, including specialized milking equipment, individual cow testing at milking time, and nutrition systems that provide each cow with the individualized ration. Forced-traffic scheme is a system that forces cows through an AMS as the only way to access feed to increase the daily number of voluntary and total milkings, which increases the milk yield. Forced traffic, however, alters the eating behavior of cows and decreases the number of daily meals and is not likely to improve milk production (Bach, Devant, Igleasias, & Ferrer, 2009). Mobile AMS, which has attracted interest in Europe, follows the cows to the pasture and minimizes the distance between grazing and stationed milking systems in the barn. Robotic milking has been well adapted for use on dairy farms in other countries (Gonulol, 2016). Further research on the impact of various AMSs on dairy cow management, behavior, health, and welfare may be needed to further improve these systems (Jacobs & Siegford, 2012).
Automated feeders reduce the labor and time required to feed animals. Automated calf feeders can be used to feed calves by properly mixing and feeding milk replacer or cow’s milk. Automated feeders with TMR are used to deliver more balanced diets to heifers and cows. Some of the automatic feeders are installed inside the milking parlors.
Sensors are attached to cows and can collect a myriad of information that gives dairy farmers more precise information about each cow, thereby helping manage the herd more efficiently and improve herd health and reproduction. The sensors can provide data related to the cow’s temperature, rumination, activity, or other characteristics of the individual animal. They can help producers identify health problems earlier and result in more productivity. A 3-D accelerometer sensor has been used to record feeding behavior of dairy cows (Mattachini, Riva, Perazzolo, Naldi, & Provolo, 2016).
Precision livestock production is the augmentation of precision agriculture concepts to include all components of agroecosystems, particularly animal and plant-animal interactions. Precision dairy nutrition has been defined as the use of information technology to optimize economic, social, and environmental farm performance (Spilke & Fahr, 2003). Precision nutrition encompasses the use of ear tag sensors that can be read by handheld readers through wireless transmission. It is used in combination with software such as feed formulation, livestock administration, reproductive optimization, and quality management. Readers are connected to the Internet, making it possible to process the data immediately. It recognizes individual properties of each animal and customizes individual animal’s nutritional needs. It is a system that uses advanced technologies to optimize animal production. A precision-nutrition model used to simulate the relationship between diet formulation frequency and dairy cattle performance across various climates suggested that frequent diet formulation is one of the important considerations for successful performance (White & Capper, 2013).
Nutrigenomics may be defined as a science concerned with the effect of nutrients and food or feed components on whole-body physiology and health status at the molecular and cellular levels. The precise determination of molecular mechanisms underlying animal and human health and disease offers a great potential for promoting health and lowering mortality and morbidity. The ultimate goal of molecular nutrition and nutrigenomics is that all relevant aspects of regulation of metabolism at all levels of complexity should be taken into account to describe the molecular physiology of nutritional process, nutritional system biology. Nutrigenomics in dairy cows is in its infancy. It has been suggested that integration of the functional genomics, proteomics, and metabolomics with measurements of tissue metabolism obtained by other methods is a particularly exciting prospect for the future (Drackley, Donkin, & Reynolds, 2006). The effect of t10, c12-conjugated linoleic acid on depressing milk-fat synthesis via inhibition of SREBP1 was among the first, and likely remains the best-known, nutrigenomic example in dairy cows, with fatty acids, amino acids, level of feed, and energy intake having the strongest nutrigenomic potential (Bionaz, Osorio, & Loor, 2015).
Dairy Production and the Society
From the early recognition that milkmaids (women who milked cows) seemed to be immune from the smallpox plagues that swept through Europe in the 18th century to the milk labeling controversy over rbST in the late 20th century, dairy operations and the industry interact with human society meticulously. On March 23, 1883, a “milk war” between U.S. milk producers and distributors resulting from a price disagreement led to milk dumping and, eventually, to a resolution of the pricing disparity. On September 19, 1913, the New York Times reported that a large typhoid epidemic in New York City had been attributed to contaminated milk. Mandatory pasteurization of milk began in 1917. Dairy farmers went on strike over low milk prices both in 1933 in Sioux City, Iowa, and in 1939 in New York City. The Dairy Act of 1983 created a National Dairy Board in the United States to promote increased human consumption of milk and dairy products and reduce milk surpluses. The first USDA Food Pyramid, released in 1992, recommended daily consumption of 2 to 3 servings of milk and other dairy products. In 1993, the California Milk Processor Board launched the “Got Milk?” advertising campaign in. It is considered one of the most important and successful campaigns in history.
Perhaps the most significant structural change in dairy production after WWII was the consolidation of dairy operations. In the early 21st century, the number of dairy operations continues to decrease, while herd size in the remaining operations continues to increase. These structural changes are driven by competition from larger dairy operations, lack of generational interest, shortage of on-farm labor, increased safety and environmental regulations, and urbanization. Structural changes in milk-production operations affect society in various ways.
The number of small dairy farms as a way of rural living for many generations is declining. Increasingly, these smaller dairy operations rely on off-the-farm income and hired labor to be able to continue operation. Some smaller, specialized dairy operations are able to persist because of niche markets. There is also concern about the decrease in medium-sized dairy operations in the face of competition from large, industrialized dairy operations. Through the modest expansion of existing operations, the embrace of modernization, and an influx of younger farmers, medium-sized farms operated by older farmers who are reluctant to change their way of living are able to persist. In reviewing of the effect of production systems, adoption of a managed grass or pasture-based dairy technique is essential for the survival of small- and medium-sized dairy farms in the face of increased competition from large confinement dairies (David, Campbell-Arvai, & Rozeboom, 2009).
Large commercialized and industrialized dairy operations impact communities socially, economically, and environmentally in ways that can be both positive and negative (Lobao & Stofferahn, 2008). The introduction of rbST, TMR machinery, freestall barns, and more efficient milking parlors has enabled large dairy operations to produce milk more cost-effectively. Some of these large operations integrate with markets vertically and benefit consumers with a reasonable pricing for milk. These large operations provide employment opportunities for the local community, although they also rely increasingly on imported labor. Increased retail sales often mean increased community income. Concomitantly, declines in property values, higher crime rates, and less civic involvement also observed. Dairy herd size was positively correlated with complaints about air and water pollution and negatively correlated with community interaction and local input purchases (Foltz, Jackson-Smith, & Chen, 2002; Jackson-Smith, 2005).
Animal Behavior and Welfare
Production systems, such as mixed, intensive, extensive, and organic; housing systems, such as tie stalls, freestalls, and loose housing; and management systems for feeding, milking, processing animal waste, and flooring can modify animal behavior and affect animal welfare. The effects of confinement on cow comfort, social behavior, health (e.g., mastitis and lameness) and fertility were the early foci on dairy-cow welfare. Increased stocking density displaced cows more often from feeding areas; daily feeding times were greater; and the duration of inactive standing in the feeding area ware less when using a post-and-rail compared with a headlock feed barrier (Huzzey, DeVries, Valois, & von Keyserlingk, 2006). Prolonged waiting time at the milking parlor, large feeding groups, and higher stocking density limited dairy cows’ opportunities to behave normally, and was seen in decreased ruminating (Dijkstra, Veermäe, Praks, Poikalainen, & Arney, 2012). Welfare quality, measured by a range of assessments in feeding, housing, health, and behavior of dairy cows, was found to be better in the tie-stall farms, which allow exercise at paddocks and pasture than in those that do not (Popescu, Borda, Diugan, Spinu, Groza, & Sandru, 2013). The longevity of dairy cows, as affected by culling due to foot disorders, is viewed as an animal welfare issue (Bruijnis, Meijboom, & Stassen, 2013).
Welfare issues related to the basic animal needs to be free of thirst, hunger, and disease are value-related, and consensus among producers, consumers, and scientific community can often be reached. On the other hand, production and management systems that affect animal response and behavior are often debatable among stakeholders. For example, an intensive system involving confinement can be perceived simultaneously as a negative in terms of crowdedness and promoting aggression and as a positive in providing an environment of free of harsh weather and parasites, in comparison to extensive systems involving free grazing. While genetic selection and nutrition have contributed to the tremendous progress in production efficiency in dairying, the effects of genetic selection for high milk production on mastitis, lameness, longevity, and fertility, and the effects of feeding high concentrate on rumination and metabolic disorders continue to be discussed among stakeholders. Recognizing that domestication has modified the behavior of cows, understanding cows’ communication, biological rhythms, sleep patterns, aggression, social structures, and maternal, sexual, ingestive and learning behaviors will not only provide scientific bases for animal welfare discussions but also serve as informatics for management decisions. A new technology that utilizes data collected from a neck-mounted tri-axial accelerometer with a simple decision-tree classification algorithm seems to be promising for the automated-detection of health and welfare problems in dairy cows (Vázquez-Diosdado, Barker, Hodges, Amory, Croft, Bell et al., 2015). Increasingly, a school of thought in promoting natural animal behavior and living is gaining footholds among not only consumers but also behavior scientists (Bruijnis et al., 2013), despite differences in value perception and criteria setting. Access to pasture is increasingly viewed as a way to alleviate stress and to promote natural living of cows. Newer generations of consumers are increasingly sophisticated and willing to pay more for products, such as organic ones, to promote environmental sustainability and animal welfare. The welfare of farm animals is among the top three issues that European consumers want to know more about, after safety and quality of foods, and the effect of agriculture on environmental and climate change (Eurostat, 2011). While the debates will continue, the cost of promoting natural animal behavior and living will have to be shared among stakeholders.
Organic dairy farming is growing. Consumers increasingly view organic dairy production as an appropriate way of both farming and rural living. Consumers and producers have increasingly viewed animal welfare, environmental preservation, product safety, and health benefits as important considerations for consuming and producing organic dairy products. Barham, Brock, and Foltz (2006) compared conventional, organic, and management-intensive rotational grazing dairies and found that organic production resulted in larger price premiums for milk and greater quality of life for the farmer. Organic dairy farmers also reported greater optimism about the future viability of their dairy operations than did either management intensive rotational grazing or conventional farmers.
Beginning 8,000 to 10,000 years ago, Neolithic farmers in the Near East started keeping small herds of cattle, goats, and sheep to supply both their milk and meat, and also used animal hair bone, skin, and sinew to make clothing and in building. Undoubtedly, dairy farming at the time was organic. Mechanical (1880–1930) and chemical (1920–1950) revolutions in agriculture greatly influenced modern-day livestock farming that was predominately nonorganic. Biological advances in genetically modified organisms (GMOs) in the 1970s further complicated the researcher–producer–consumer dynamics. Because GMOs are prohibited in organically certified products, organic dairy appeals to consumers who are wary of the health uncertainties of GMOs.
Rudolf Steiner (1861–1925), considered one of the founders of organic farming, proposed a form of agriculture called “biodynamics,” drawing inspiration from cosmic and telluric forces. The concepts of humanity and living things were introduced into agriculture; the word biodynamics is from the Greek words for life (bios) energy (dynamis). Biodynamic agriculture, or biodynamics, is an ecological farming system that includes many of the ideas of organic farming, but predates that term. Biodynamic agriculture emphasized the individualization of the farm by bringing in no or few outside materials. Degradation of food quality was attributed to chemical farming, artificial fertilizers, and pesticides. There was a belief the philosophical theory known “monism,” which holds the world and everything in it are simultaneously spiritual and material in nature, and that spiritual deficits could adversely affect the quality of food.
Biodynamic agriculture was introduced in 1924. Rodale Farm, established in 1947, was the first modern-day organic farm in the United States. Sir Albert Howard, who wrote about what he had learned about organic farming practices in India during the 1920s, contributed the organic farming movement that began in England in the 1940s. Modern-day organic farming began to emerge in the 1950s, and there were major developments in the 1970s. A certification system for foods marketed and sold as organic was implemented in the 1980s. In the 1990s popularity of organic foods soared, and organic dairy became one of the major categories of organic agriculture.
Organic Agriculture at a Glance
Global turnover for organic farming is reported to be US$80 billion (Willer & Lernoud, 2016) and has grown continuously over the past 10 years. Industry experts expect that demand will continue to grow in many markets. The international organic market is expected to reach US$100 billion in the next few years. According to the Organic Trade Association, total U.S. organic sales, including food and nonfood products, were estimated to have reached $35.9 billion in 2014. In Europe, Germany and France are the leaders in organic sales, at $10.5 billion and $6.8 billion, respectively. Eighty-seven countries currently have regulations on organic agriculture. In 2015, the International Federation of Organic Agriculture Movement had 784 affiliates, from 117 countries, worldwide (Willer & Lernoud, 2016).
Organic agricultural land, which reached 43.7 million hectares in 2013, continues to increase.. A recent and significant development in organic agriculture is the increase in wild collection. In 2014, there were 37.6 million hectares of these nonagricultural organic areas worldwide. Sixty-three percent of organic agricultural land is permanent grassland, which has implications for ruminant livestock production, including dairy. Australia is the leading country in organic agricultural land area, at more than 17 million hectares, followed by Argentina, the United States, China, and Spain. More than 2.3 million organic producers were reported worldwide and more than three quarters of the producers are located in developing and transition countries (Willer & Lernoud, 2016). India, with more than 650,000 organic producers, leads, followed by Uganda and Mexico.
There are three major reviews of organic products and human health research that reached very different conclusions. A group of scientists (Dangour, Dodhia, Hayter, Allen, Lock, & Uauy, 2009) published a major review of organic versus conventionally grown food, covering research from 1958 through 2008. They reviewed 52,471 articles and found 162 studies that compared crops and livestock products. Of these, they selected 52 of the highest quality studies for inclusion in their analyses. They found no significant difference between organic and conventionally grown food with respect to nutrient content. The small differences in nutrient content detected were biologically plausible and mostly related to differences in production methods. Researchers from Stanford University (Smith-Spangler, Brandeau, Hunter, Bavinger, Pearson, Eschbach et al., 2012) published a systematic review and meta-analysis. Looking at research through May 2011, they found 460 studies, and identified 237 that met their inclusion criteria. Among those, 17 were studies of human diets and 223 were studies of foods themselves. They found a lack of evidence that organic foods were significantly more nutritious than conventionally grown foods but that consuming organic foods may reduce exposure to pesticide residues and antibiotic-resistant bacteria. A study based on 343 peer-reviewed publications indicated statistically significant and meaningful differences in the compositions of organic and nonorganic crops or crop-based foods (Barański, Srednicka-Tober, Volakakis, Seal, Sanderson, Stewart et al., 2014). They concluded that organic crops were more nutritious and up to 60% higher in a number of key antioxidants than conventionally-grown ones. Organic crops, on average, had higher concentrations of antioxidants (phenolic acids, flavanones, stilbenes, flavones, flavonols, and anthocyanins), lower concentrations of Cd, and a lower incidence of pesticide residues than the nonorganic comparators across regions and production seasons.
Organic Dairy in the World
The demand for organic milk continues to grow. The United States, the United Kingdom, France, Australia, China, and Germany are the key markets for organic milk (Report Linker, 2016). The global market for organic dairy products is highly fragmented due to the presence of numerous small and big vendors. Competition is expected to intensify because of the influx of private providers. Europe was the dominant region in 2014, accounting for around 35% of the global market share in organic dairy products. The ongoing introduction in the market of innovative organic dairy products, such as flavored organic-milk drinks and energy-based milk drinks has been driving the market growth in Europe. The report (Report Linker, 2016) predicts that Europe will maintain its market leadership until the end of 2019. Among EU member states, only 3% of total dairy cows are used in organic dairy operations (European Commission, 2013). The countries with the largest share of organic dairy cows are Austria (18%), Sweden (12.7%), Denmark (10.9%), and the United Kingdom (8.1%). France, the second largest dairy producer in the EU, has over 2% of total dairy cows in organic operations. The organic goat sector would count almost 0.4 million heads, mostly concentrated on cheese production (European Commission, 2013). In Greece, which has the largest goat population in the EU, 4.1% of all goats are organic, used in the production of organic cheese, such as feta. The organic goat herd as a percentage of total population is 52.9% in Austria, 49% in Latvia, 31.5% in Estonia, 29.1% in the Czech Republic, 17.5% in Slovenia, 8.7% in Ireland, 7.5% in Italy, and 6.4% in the Netherlands. It appears that the proportion of organic herd in the total population is much larger for goats than cows, suggesting a dominance of organic goat dairy.
In the United States, the total sales of organic milk products for January 2016 were up 4% from January 2015 (Organic Dairy Market News, 2016). Total organic whole-milk-product sales up 13.4% in the same time period.. The compound annual growth rate for the organic dairy market during 2007–2012 in North America was 3.3%. In contrast, world growth was 3.7%, Europe (including Scandinavia) was 5.3%, and the rest of the world was 16.9%. This means that the 2007–2012 North American organic growth rates was much lower than much of the rest of world. Annual U.S. organic dairy products sales increased in 2014, but then declined slightly in 2015. Organic milk, which accounted for 50% of the market share in 2014, is predicted to reach a market value of around US$13 billion by the end of 2019. The United States has come to depend on imports to meet domestic organic dairy demand. Organic dairy imports from the EU, the United Kingdom, and Oceania have helped to meet the U.S. demand. Imports of organic cheese; dairy powders, such as whole milk powder, whey, and skim milk powder; and butter also help address domestic demand.
Between 2000 and 2005, the number of certified organic milk cows on U.S. farms increased annually by an average of 25%, from 38,000 to more than 86,000 (McBride & Greene, 2009). Forty-five percent of organic dairies milk fewer than 50 cows, and 87% milk fewer than 100 cows. A smaller portion of organic dairies has 200 cows or more, but accounts for more than a third of organic milk production in the U.S.
The U.S. organic dairy industry started in the Northeast and the upper Midwest. Similar to conventional dairies, herd sizes are smaller in the Northeast (averaging 54 cows) and upper Midwest (64 cows) than the West (381 cows; McBride & Greene, 2009). Organic dairies in the Northeast and upper Midwest utilized more pasture and home-grown feed, resulting in a lower average feed cost. Labor cost is higher in the West due to need for hired labor by the larger size operations. The West produces more milk per cow on average (1,227 kg more than in the upper Midwest and 1,818 kg more than in the Northeast; McBride & Greene, 2009). Organic dairies that use conventional feeding methods, such as confining cows and feeding harvested forages, may generate higher returns to capital and labor than those using pasture-based feeding because of higher production and economies of scale. It seems that organic dairies may follow the same trend of structural change and migrate to larger and more efficient sizes of operation. However, the requirement for pasture for the certification process and the availability of large amounts of organic feeds may limit the pace of such structural change.
There are differences in the operational characteristics between conventional and organic dairies. McBride and Greene (2009) summarized those differences as follows: (1) organic dairies were smaller than conventional dairies (82 cows compared to 156 cows); (2) organic dairies produced about 30% less milk per cow than conventional dairies; (3) in the United States, organic dairies were more often located in the Northeast and the upper Midwest than conventional dairies (86% compared to 65%); (4) organic dairies used more pasture-based feeding, where more than 50% of dairy forage fed is from pasture during grazing months, than conventional dairies (63% compared with 18%); (5) organic dairies paid more than conventional dairies in operating and capital costs, including transition costs; (6) total economic costs of organic dairies in 2005 were $0.17 per kg of milk higher than conventional dairies and nearly $0.02 per kg of milk higher than the average price premium for organic milk; and (7) total economic costs of pasture-based organic dairies were about $0.09 per kg of milk higher than conventional pasture-based dairies, much lower than the average price premium for organic milk in 2005.
Organic Dairy and Human Health
The health and nutrition benefits of organic products are among the considerations of sophisticated consumers when choosing organic dairy products over conventional ones. It has been stated that the proliferation of rbST use, genetically modified grains, livestock feed crops sprayed with synthetic pesticides, the feeding of rendering byproducts and mad cow disease, and the use of synthetic hormones, antibiotics, and steroids have encouraged many consumers to seek organic dairy products (Hamadani & Khan, 2015).
Some reported benefits of consuming organic milk are attributed to the higher content of beneficial fatty acids (FA). Conjugated linoleic acid (CLA), trans-vaccenic acid (TVA), and linolenic acid (LNA) in organic bulk milk were higher in comparison with conventional samples in Italy, largely due to the forage diets fed to organic herds (Prandini, Sigolo, & Piva, 2009). A 12-month study (Collomb, Bisig, Bütikofer, Sieber, Bregy, & Etter, 2008) that compared conventional milk with organic milk in the Switzerland Mountainous region indicated that organic milk had significantly higher contents of polyunsaturated FA (PUFA), CLA, n-3 FA, and branched FA. Levels of CLA and TVA in human milk can be modulated if breastfeeding mothers replace conventional dairy or meat products with organic ones, suggesting a potential contribution of CLA and TVA in organic dairy food to health improvement (Rust, Mueller, Barthel, Snijders, Jansen, Simões-Wüst et al., 2007). Organic milk had higher concentrations of beneficial FA than conventional milk, including total PUFA, CLA, cis-9, trans-11, and α-LNA (Butler, Stergiadis, Seal, Eyre, & Leifert, 2011).
Organic milk was implicated in the improvement of ω-6/ω-3 fatty acids intake ratios that is considered beneficial in human health. Omega-3s are linked to reductions in cardiovascular disease, improved neurological development and function, and better immune function. A nationwide study (Benbrook, Butler, Latif, Leifert, & Davis, 2013) of fatty acids in U.S. organic milk and conventional milk over 12 months concluded that organic milk contained 25% less ω-6 fatty acids and 62% more ω-3 fatty acids than conventional milk, yielding a 2.5-fold higher ω-6/ω-3 ratio in conventional compared to organic milk (Benbrook et al., 2013). All individual ω-3 fatty acid concentrations were higher in organic milk—α-LNA (by 60%), eicosapentaenoic acid (32%), and docosapentaenoic acid (19%)—as was the concentration of conjugated linoleic acid (18%). A meta-analysis with Hedges’ d effect-size method was used specifically to compare conventional versus organic dairy products (Palupi, Jayanegara, Ploegera, & Kahl, 2012). It was concluded that organic dairy products contained significantly higher ω-3 to ω-6 ratio and Δ9-desaturase index with higher protein, ALA, total omega-3 fatty acid, cis-9, trans-11 CLA, trans-11 TVA, eicosapentanoic acid, and docosapentanoic acid than those of conventional dairy products.
Information pertaining to a direct link between organic milk and human health is scarce. One exception is that consumption of organic dairy products was associated with lower eczema risk in a study that investigated whether organic food consumption by infants in the Netherlands was associated with developing atopic manifestations in the first two years of life (Kummeling, Thijs, Huber, van de Vijver, Snijders, Penders et al., 2008).
There are several opportunities that may impact the future of organic dairy. Global acceptance and appreciation of organic dairy products is an important opportunity for the future growth of organic dairy markets. While energy and chemical costs are high, practicing sustainable organic dairy production in general has an economic edge. Alternative medicine as a result of prohibition of the use of restricted materials to treat diseases and illnesses can be promising (Lu, 2011). Grazing of minor dairy species, such as dairy sheep, dairy goats, and camels on marginal land that is organic through wild collection can bring additional income to producers (Lu, Xu, & Kawas, 2010).
A number of research opportunities are also apparent. The list includes emerging health issues, welfare and production constraints, epidemiological surveillance of key production diseases, breeding studies on disease resistance and commercial traits, nutritional deficiencies in organic systems, livestock breeding, biological control and the use of novel plants and plant extracts, development of animal-welfare assessment methods, and development of welfare-friendly production systems (Lu et al., 2010).
Animal health and welfare, with a greater emphasis on disease control and eradication, will likely be the main challenge for organic dairy production in the future. To accomplish the goals of disease prevention, control, and eradication, the monitoring and evaluating of alternative health products will gain importance. Capitalizing on the opportunity to use marginal land, the lesser-developed regions will most likely pursue converting hill and upland systems to organic production in in the future. Due to the extensive use of grazing in organic dairy production, mineral deficiencies as a result of soil characteristics and pasture management systems should be important considerations. In addition, prevention of fraud and quality assurance for organic dairy products will continue to be a concern for consumers.
Organic dairy production can improve animal welfare, protect the environment, and sustain rewarding rural lifestyles. Traditional and alternative medicine hold promise for alternative approaches to the prevention and treatment of animal diseases. The future of organic dairy production is to continue searching for alternatives that are environmentally friendly, human-health conscientious, and animal considerate. Understanding organic dairy farming from economic, ecological, and animal-welfare perspectives will increase the likelihood of success. Organic dairy production will have to strive for a more environmentally and economically sustainable system than the conventional ones, offsetting the increased costs of organic production with higher product prices, and to produce certified organic dairy products that are healthier than those that are conventionally produced. Further, to reduce environmental costs organic dairy will have to address lower production levels and production efficiency.
Dairy Production and the Environment
Greenhouse Gas Emission from Dairy
“Global warming” is a term that is used to describe a gradual increase in the average temperature of the Earth’s atmosphere and its oceans. It is believed to be permanently changing the Earth’s climate. Carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are the gases that are mainly responsible for atmospheric warming, or the “greenhouse effect,” in addition to chlorofluorocarbons, sulphur hexafluoride, hydrofluorocarbons, perfluorocarbons, and ozone in the atmosphere (Takahashi, 2013). The unique gastrointestinal tract, large populations, body size, and appetite in ruminants result in global atmosphere emissions of mainly CO2, CH4, and N2O. These gases are considered anthropogenic, meaning that they result in environmental pollution caused by human activity. Global atmospheric concentrations of these three most important and long-lived greenhouse gases have increased measurably over the past 250 years. The sources of these emissions can be attributed directly or indirectly to ruminants, including dairy cattle, goats, sheep, and buffalo.
Over the past decades, large dairy operations have faced many environmental issues in relationship to elevated greenhouse gas emissions. Capper et al. (2009) reported that modern dairy systems produce 24% of the manure, 43% of CH4, and 56% of N2O per billion kilograms of milk compared with equivalent milk from historical dairying in 1944. They also indicated that the carbon footprint per billion kilograms of milk produced in 2007 was 37% of that of the equivalent milk production in 1944. Although modern dairies are more efficient and produce considerable less manure and greenhouse gases per unit of milk produced, the total output of CH4 and N2O is still larger compared to that of 1944. This is because of the continuous increase in total milk production since 1944. There is also a geographical disparity in greenhouse gas emissions in terms of per unit of milk produced. Although North America and Western Europe produce the largest amount of milk, greenhouse gas emissions in proportion to milk production is higher in Africa and Asia (Opio, Gerber, Mottet, Falcucci, Tempio, MacLeod et al., 2013). There has been a gradual increase in methane emissions from enteric fermentation in dairy cattle since the U.S. Environmental Protection Agency (EPA) began documenting methane emissions in 1990. In terms of per unit of milk produced, small ruminants appear to emit more greenhouse gases than large ruminants. In terms of meat production, small ruminants emit less greenhouse gas per unit of carcass weight. Average emission intensity for products from ruminants was estimated at 2.8, 3.4, and 6.5 kg CO2-eq/kg fat and protein corrected milk (FPCM) for cow, buffalo, and small ruminant milk, respectively, and 46.2, 53.4, and 23.8 kg CO2-eq/kg carcass weight (CW) for beef, buffalo, and small ruminant meat, respectively (Opio et al., 2013).
Dairy cattle are only second to beef cattle as the largest livestock contributors to methane emissions (Figure 3).
Feed quality, land-use, manure management, and the size of dairy operations influence the amounts of greenhouse gas emissions. It appears that when geographical locations and production systems were considered, grassland in arid and humid areas contributed to higher proportion of greenhouse emissions than did mixed systems in temperate areas (Opio et al., 2013). Regional emission intensity of milk ranges from 1.6 kg to 9.0 kg CO2-eq/kg FPCM. Generally, milk production in low-productive systems has higher emission intensities than in the high-production systems of most affluent counties, where better animal feeding and nutrition results in lower enteric and manure emissions, as well as emission intensity, at the animal level.
In a dairy operations, both feed production and non-feed production are sources of CO2emissions. The CO2 produced in feed production includes energy use in field operations, energy use in feed transport and processing, fertilizer manufacture, land-use change related to deforestation, soybean and pasture expansion, and changes in carbon stocks from land use under constant management practices. The CO2 produced from non-feed production included indirect energy related to the manufacture of on-farm buildings and equipment, production of cleaning agents, antibiotics, and pharmaceuticals. Diary production also has on-farm carbon emissions, such as energy use in milking, cooling, ventilation, and heating, and off-farm carbon emissions from the transport of live animals and products, emissions of animal waste, and waste disposal. Both CH4 and N2O can be converted using 100-year global warming potentials (GWP) relative to CO2 for ozone-depleting substances and their replacements. Based on the Intergovernmental Panel on Climate Change Fourth Assessment Report (AR4), emissions of CH4 and N2O can be converted to CO2-eq by a factor of 25 and 298, respectively (Forster, Ramaswamy, Artaxo, Berntsen, Betts, Fahey et al., 2007). It means that releasing 1 kg of CH4 into the atmosphere is about equivalent to releasing 25 kg of CO2 and releasing 1 kg of N2O into the atmosphere is about equivalent to releasing 298 kg of CO2. In the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, CH4 has a lifetime of 12.4 years and with climate-carbon feedbacks a global warming potential 34 over 100 years in response to emissions (Myhre, Shindell, Bréon, Collins, Fuglestvedt, Huang et al., 2013). In that report, a factor of 34 for CH4 was used and N2O remained at 298. In the United States, the EPA uses 21 and 310 CO2-eq 100-year GWP for CH4 and N2O, respectively (United States Environmental Protection Agency, 2014).
Estimating Emissions in Dairy Cows
Various methods are used to acquire accurate levels of CH4 being produced including sulfur hexafluoride (SF6), whole animal respiration chambers, and a ventilated hood system. The whole-animal respiration chamber appears to be the most accurate and is used as the standard. The SF6 technique is the most affordable and widely used, but it is less accurate than the whole-animal respiration chamber owing to the influence of permeation rates of SF6 (Lassey, Pinares-Patiño, Martin, Molano, & McMillan, 2011). Despite an influence of permeation rate on CH4 emission estimates, accuracy and precision of the tracer technique is warranted provided that permeation rates are used in a narrow range and are balanced among the experimental treatments (Pinares-Patiño, Machmüller, Molano, Smith, Vlaming, & Clark, 2008). Gas capture rates for the ventilated hood technique ranges from 97.6%– 99.3%, which is more accurate than the SF6 method, and cheaper than whole animal respiration chambers (Place, Pan, Zhao, & Mitloehner, 2011). Compared to the measurement of CH4 emissions from lactating dairy cows using the SF6 tracer versus open-circuit respiration chamber techniques, the SF6 tracer technique was reasonably accurate for inventory purposes and for evaluating the effects of mitigation strategies on CH4 emissions (Grainger, Clark, McGinn, Auldist, Beauchemin, Hannah et al., 2007).
Measuring the greenhouse gas emissions for entire herds is considered more reflective and relevant than measuring the emissions of individual animals. Sulfur hexafluoride (SF6), whole-animal respiration chambers and the ventilated hood system are mainly used for individual animals. Methods of measuring greenhouse gas emissions of an entire herd that are transported and dispersed by the wind include the external tracer-ratio technique, micrometeorological mass-budget technique, and backward-Lagrangian stochastic technique (Laubach, Kelliher, Knight, Clark, Molano, & Cavanagh, 2008; Laubach, Bai, Pinares-Patino, Phillips, Naylor, Molano et al., 2013). In the micrometerological technique, wind transport of the emitted gas away from the animals is used as a vehicle to determine emission rates (Harper, Denmead, & Flesch, 2011). Wind speed, direction, and turbulence parameters are measured, as is the CH4 concentration in the air. This technique is unobtrusive to the animals and thus represents their normal behaviors and physiology. For grazing cows, Griffith, Bryant, Hsu, and Reisinger (2008) employed a technique using N2O as a tracer at the upwind edge of the feeding strip, and measured the downwind concentrations of N2O and CH4 simultaneously using Fourier transform infrared spectroscopy (FTIR). They also used the integrated horizontal flux (IHF) technique and 1-D mass-balance method, measuring vertical profiles of CH4 concentration and the speed of downwind to the cows to determine the total CH4 emission. Micrometeorological techniques for measuring CH4 emissions from dairy cow herds that freely graze has been described (Laubach & Kelliher, 2004, 2005a, 2005b). To facilitate whole-farm CH4 measurements across a number of pastures, open-path lasers can be combined with micrometeorological dispersion methods to measure enteric CH4 emissions from herds of animals (Laubach et al., 2013). Measurements are performed using one or more tunable infrared diode lasers mounted on a programmable vehicle.
The photoacoustic field gas-monitor uses optical filters to measure gas that absorbs infrared light. This technique has a high stability so that frequent calibration is not required. It is also accurate because it compensates for temperature and pressure fluctuations, water-vapor interference, and interference from other known gases. The photoacoustic field-gas monitor presents measurements via a connected personal computer in both tabular and graphic forms. Advancements, such as the use of quantum cascade laser for radiation sources, the optical parametric oscillator system, the differential photoacoustic cell, and the simple resonant photoacoustic cell for the improvements in the detector enable the detection of greenhouse gases and their precursors in the ppmv and ppbv range (Sthel, Gomes, Lima, Vieira, Rocha, Schramm et al., 2012).
The mitigation of enteric CH4 emission in dairy cows is important environmentally as well as economically. Methane produced as a byproduct of microbial fermentation in the rumen represents a net energy loss for dairy cattle. Methane emission from dairy cows represents one of the largest greenhouse gas emission loads among the livestock sectors. There are known mitigation strategies for dairy cattle, such as use of high-quality forages, increasing the concentrate-to-forage ratio in the diet, protein supplementation of low-quality forage, and inclusion of fat. These are nutritional strategies that can be applied as long as they do not compromise normal rumen function and milk production. Additives, mostly CH4 inhibitors, have also been identified. These include ionophors, probiotics, acetogens, bacteriocins, archaeal viruses, organic acids, and plant extracts. Their effectiveness has not been consistent, and they may not be cost effective.
Suppression of CH4 production by lipids in the rumen is widely known. Lipids are known to inhibit the growth of both methanogens and protozoa. Woodward, Waghorn, and Thomson (2006) examined the effect of vegetable and fish oils on milk production and CH4 emission in both short- (14-day) and long-term (12-week) experiments. Lipids significantly decreased CH4 production in the short-term, but this effect diminished after 11 weeks of feeding. Lipid supplementation is not always practical in pasture-based operations.
Among methanogenesis inhibitors, the most promising are bromochloromethane, chloroform, and 3-nitrooxypropanol. Bromochloromethane reduced CH4 production without affecting feed intake, growth rate, or digestibility in cattle and sheep (Gerber et al., 2013a). Chloroform reduced CH4 emission by 38% after adaptation, without adverse effect of rumen function in cows (Knight, Ronimus, Dey, Tootill, Naylor, Evans et al., 2011). The use of 3-nitroocypropanol reduced CH4 emissions by 30% and increased milk production and growth rate without affecting intake and digestibility in dairy cows over a 12-week period (Hristov et al., 2015).
Vaccination against rumen methanogens has the potential to reduce CH4 emissions by decreasing the number or activity of methanogens in the rumen. This option may be practical for pasture-raised animals using a relatively easy vaccination procedure. The approach would involve vaccinating animals to generate a substantial salivary antibody response that delivers a high yield of antibodies to the rumen to neutralize methanogens and impairs their CH4 formation. The results are not always consistent (Wright, Kennedy, O’Neill, Toovey, Popovski, Rea et al., 2004). Four weeks post secondary immunization, there was a 7.7% reduction in CH4 production per kilogram of dry matter intake in sheep immunized with a 3-methanogen mix. Immunization of a 7-methanogen mix on day 0 followed by a 3-methanogen mix on day 153 was not effective (Wright et al., 2004). A highly specific vaccine to target specific strains of methanogens is possible but a more broad-spectrum approach is needed for the success in the rumen (Williams, Popovski, Rea, Skillman, Toovey, Northwood, 2009). The vaccination with recombinant protein EhaF caused intensive immune responses in serum and saliva, but had no significant effect on total enteric CH4 emissions and methanogen population in the rumen (Zhang, Huang, Xue, Peng, Wang, Yan et al., 2015).
Bacteriophages are viruses that attack bacteria and infect it by reproducing inside the cell. Phage therapy is based on the idea that a bacteriophage is used as a vehicle for exchanging genetic information. When a modified genome is inserted into the bacteria, the new gene information is incorporated into the DNA of the existing cell, which disrupts the process of bacterial cells and kills them without harming the host. Phage-based mitigation strategies use specificity to target specific methanogen groups without affecting other microbes in the rumen (Buddle, Denis, Attwood, Altermann, Janssen, Ronimus et al., 2011). However, it is difficult because the host changes to try to get rid of the infection and the phage changes to try to maintain infectivity. The use of a rotation system could overcome the constant struggle between the host and the phage, but more methanogen phages need to be found (Buddle et al., 2011). The high specificity of phages may limit their effectiveness in reducing the total methane emissions, since there appears to be a high diversity of methanogens in the rumen (Janssen & Kirs, 2008). There are about 300 known bacteriophages, but only six archaeal phages have been studied and only two of these are methanogens. The two bacteriophages that have been discovered are Methanobacterium phage psi M1 and M2 (Pfister, Wasserfallen, Stettler, & Leisinger, 1998), and Methanothermobacter phage psi M100 (Luo, Pfister, Leisinger, & Wasserfallen, 2001). Since there are other types of methanogens in a ruminant’s stomach, more investigations will have to be conducted before phage therapy can be a viable method to pursue (Buddle et al., 2011).
Homoacetogens are H2 utilizing acetogenic bacteria that are found in the rumen, using H2 as an energy source for growth and reducing CO2 to acetate. They can redirect rumen fermentation and reduce feed energy loss as CH4. There are homoacetogens that naturally occur in the rumen; however, there are other methanogens that compete for the use of H2. Homoacetogens do not limit the activity of the methanogens themselves, but can be a valuable tool for the utilization of the H2 produced by the fermentation of feed (Buddle et al., 2011). Acetogenic bacteria can utilize H2 and CO2 to form acetate in the rumen when methanogenesis is inhibited, but large concentrations of acetogenic bacteria cannot compete for H2 with methanogenic archaea under normal circumstances (Lopez, McIntosh, Wallace, & Newbold, 1999). Like most of the other methane-reducing options, its effectiveness is still to be established.
Genetic selection for dairy ruminants with traits of lower CH4 emissions can be promising. Based on the assumption that residual gain in cattle is related to number of methanogens, there is potential to adopt genetic and genomic selections for reduced CH4 emissions from ruminants (Hegarty, Goopy, Herd, & McCorkell, 2007). A predicted methane emission trait from feed and energy intake and requirements based on milk yield, live weight, feed intake, and condition score has been evaluated from a data set of 1,726 dairy cows, collected since 1990 by Pickering, Chagunda, Banos, Mrode, McEwan, and Wall (2015). From their study it appears that if routine and cost effective measurement for CH4 emissions is available, it is possible to genetically select dairy cattle with traits of low enteric methane.
There have been reviews of CH4 emission in dairy cows (Boadi, Benchaar, Chiquette, & Massé, 2004; Knapp, Laur, Vadas, Weiss, & Tricarico, 2014). Boadi et al. (2004) provided an update review of the strategies available with respect dairy cattle and concluded that mitigation of CH4 emissions can be effectively achieved using strategies that improve the efficiency of animal production, reduce feed fermented per unit of product, or change the fermentation pattern in the rumen. They emphasized that strategies that are cost-effective, improve productivity, and have no potential negative effects on livestock production have a greater chance of being adopted by producers. Knapp et al. (2014) evaluated options that have been demonstrated to mitigate enteric CH4 emissions per unit of energy corrected milk (CH4/ECM) from dairy cattle. They used a nutrition model based on carbohydrate digestion to evaluate the effect of feeding and nutrition strategies on CH4/ECM. The meta-analysis quantifies the effects of lipid supplementation on CH4/ECM. They combined herd structure dynamics and production level to estimate the effect of genetic and management strategies on CH4/ECM that increase milk yield and reduce culling. They concluded that nutrition and feeding approaches may be able to reduce CH4/ECM by 2.5% to 15%; whereas rumen modifiers have had very little success in terms of sustaining CH4 reductions without compromising milk production. More significant reductions of 15% to 30% CH4/ECM can be achieved by combining genetic and management approaches, including making improvements in heat abatement, managing disease and fertility, using performance-enhancing technologies, and designing facilities to increase feed efficiency and the life-time productivity of individual animals and herds. Genetic selection for feed efficiency, heat tolerance, disease resistance, and fertility can augment selection for milk yield to reduce enteric CH4/ECM, with potential reductions of 9% to 19% (Knapp et al., 2014).
The taskforce commissioned by Animal Production and Health Division of the FAO (Opio et al., 2013) summarized more promising mitigation of greenhouse gas emission by ruminants as (a) reducing land-use changes arising from pasture expansion and feed crop cultivation; (b) improving feeding practices and the digestibility of diets; (c) improving grazing and pasture management to increase soil organic-carbon stocks; (d) increasing milk production through genetics, feeding, and animal health; (e) improving manure management—reducing the use of uncovered liquid-manure management systems in dairy; and (f) increasing energy use efficiency, especially in the post-farm part of the supply chain. The recommendations are based on the life-cycle assessment instead of just the production unit.
Role of Secondary Plant Compounds
Naturally occurring secondary compounds in plants can be explored for their potential to reduce greenhouse gas emission in ruminants. Secondary plant compounds or metabolites, such as phenolics, alkaloids, terpenoids, and flavonoids, were associated with adverse animal responses if a sufficient quantity is accumulated in plants and ingested. At the same time, the effective prevention, control, or treatment of diseases by bioactive plants can often be attributed to secondary plant compounds. Particularly with respect to internal parasites, these naturally occurring constituents in forages are potentially inexpensive and environmentally safe alternatives to chemical anthelmintics. These secondary compounds are thought to be defense mechanisms employed by plants against ingestion by herbivores. Through selection, adaptation, and ruminal degradation, herbivores often are gradually able to consume forages containing significant amounts of secondary compounds. However, consumption of secondary compounds can at times also result in food aversion, reduced nutrient digestion and utilization, and reduced production. The bioactivities of secondary plant compounds are complex, not only because of the large number of compounds involved, in the tens of thousands, but also because of their interactions with each other and with primary plant compounds.
Secondary compounds of plants, such as saponins and tannins, have the potential to lessen CH4 emissions. In vivo and in vitro studies (Lu, Tsai, Schaefer, & Jorgensen, 1987; Lu & Jorgensen, 1987) revealed that alfalfa saponins reduced protozoa number and inhibited microbial fermentation in the rumen. The methane-suppressing effect of plants rich in saponins seems to be particularly related to their anti-protozoal effects (Beauchemin, Kreuzer, O’Mara, & McAllister, 2008). Protozoal populations were diminished when saponins containing mangosteen peel pellets were supplemented (Onanong, Metha, Chalong, Sadudee, & Anusorn, 2009). The anti-protozoal effects prevent methanogens from using the H2 in the rumen, because the removal of protozoa decreases H2 transferred from protozoa to methanogens. Protozoa numbers are generally lower in animals on forage-based diets than on grain-fed animals. Protozoal control measures may be less effective for animals on forage-based diets, such as pasture. Further long-term studies are needed, particularly of forage-only diets, to verify the overall effectiveness of farming practices that seek to control protozoa populations in the rumen.
Among plant secondary compounds, tannins are the most studied in the inhibition of methanogenesis. Their effect on the reduction of greenhouse gases, such as CH4, varies among different tannins. There is a large pool of plant sources of tannins in tropical legumes. Because of the lower risk of toxicity, research has focused on condensed tannins rather than on hydrolysable tannins (Beauchemin, McGinn, Martinez, & McAllister, 2007). Tannins suppress methanogenesis directly, by reducing methanogenic populations in the rumen, or indirectly, by reducing the protozoal population via reducing symbiotically associated methanogens. The use of tannins may reduce enteric CH4 emissions, but intake and milk production may be compromised (Hristov et al., 2015).
The effects of tannins on the parameters of rumen fermentation, protozoa population, and methanogenesis were studied in 21 medicinal and aromatic plant leaves, and the potential of these sources as antimethanogenic additives in ruminant feeds was evaluated (Bhatta, Baruah, Saravanan, Suresh, & Sampath, 2013a). Tannins in medicinal and aromatic plants, such as Clerodendrum inerme, Gymnema sylvestre, and Sageraea. laurifolia, appeared to suppress in vitro methanogenesis (Bhatta et al., 2013a). In another study, tannins from 38 sources to serve as antimethanogenic additives in ruminant diets were investigated in vitro (Bhatta, Saravanan, Baruah, Sampath, & Prasad, 2013b). The effect on gas production was highest in Alpinia galanga followed by Pelargonium graveolens and Oenothera lamarckiana with total tannins contents being 814, 884, and 185 g/kg, respectively (Bhatta et al., 2013b). The most effective in the inhibition of methanogenesis expressed as the ratio of methane reduction per milliliter of total gas reduction was Rauvolfia serpentina leaves, followed by Indigofera tinctoria and Withania somnifera. Tannins may inhibit the methanogenesis directly and indirectly via inhibition of protozoal growth (Patra & Saxena, 2010). However, using polyethylene glycol to bind tannins, methanogenesis in vitro was not essentially related to density of protozoa population and entodinia were more susceptible to tannins than holotrichia (Bhatta et al., 2013a). Feeding up to 2% of the dietary dry matter as quebracho tannin extract failed to reduce enteric CH4 emissions from cattle, but the protein-binding effect of the quebracho tannin extract was evident (Beauchemin et al., 2007). This further illustrates that although there have been successes using plant tannins to reduce CH4 emissions from ruminants, not all tannins will work for this purpose. Plant selection can be important determiners of effectiveness. The effects of the tannins from legumes on CH4 emission were studied and Lotus corniculatus and Dorycnium pentaphyllum harvested at the flower stage were reported to be the most effective (Gurbuz, 2009). Tannins inhibit methanogenesis somewhat, reducing N2O emissions up to 30%, and increase feed efficiency (Gerber et al., 2013a). However, cow milk production suffers about 10% since tannins reduce amino-acid absorption, which is essential to high-lactation yields, and more feed needs to be provided (Gerber et al., 2013a).
Dairy Waste Management
Practicing proper techniques involving applying manure and adopting an effective manure-management system in dairy can reduce the greenhouse gas emissions that plague our planet. The composition of manure is dependent on the diet, growth rate, and type of production, which also affects the amount of CH4 that is produced. The common manure-management systems are conventional manure management, covered lagoons, composting, and anaerobic manure digesters.
A conventional manure-management system is the simplest and most widely used by small dairy operations. It is the least labor-intensive and least costly of all of the manure-management systems. In conventional manure management, manure is collected from the animal pens and heaped, usually, on top of a nonpermeable flooring, such as concrete, under a top or roof to protect it from the rain and direct sunlight. Keeping the manure dry decreases the production of N2O and the risk of contamination from the environment. However, conventional manure-management systems are not efficient in decreasing the production of greenhouse gases. Because the manure is placed in a heap and is not aerated, it provides an anaerobic environment for microorganisms that break down and decompose the manure, producing CH4 and N2O.
Covered lagoon manure-management systems are widely used by large animal operations. This system involves placing manure in a pit and covering it with a barrier that is impermeable to gases, such as plastic. In the pit, the liquid portion of the manure separates from the solid portion, creating an aerobic environment that favors the production of CH4. The CH4 is then collected as biogas to be used for energy purposes. The major disadvantages of this system are that the covers can easily become damaged or may not be secured correctly, causing the CH4 produced to be released into the atmosphere. If the lagoon is agitated, it allows oxygen into the lagoon that will increase the N2O production. But because the methane-collecting mechanism is expensive, many farms do not cover their lagoons. The combustion of CH4 generates CO2, which is also a greenhouse gas (Gerber, Henderson, & Makkar, 2013a). Other hydrocarbon gases may be present in the covered lagoon that are potentially dangerous to people’s health.
Composting is a relatively simple manure-management system. In a composting system, manure is collected and put in a pile, just as in conventional manure-management practices. The difference between conventional manure management and composting is that in composting the manure is placed on an aerating system, which provides oxygen to the entire pile of manure. Aeration causes the manure to be broken down in an aerobic environment, resulting in less or no CH4 being produced. However, because the manure is still broken down, minute concentrations of N2O and CO2 produced. The amount of CO2 produced, however, is less than is produced in covered lagoons. An advantage of this system is that the manure becomes a compost that is a nutrient-rich soil amendment. The compost can be applied to soils in place of fertilizer, which is a major culprit in N2O emissions.
Anaerobic manure digesters, or CH4 digesters, operate on the same principle as covered lagoons (Figure 4).
The system involves placing manure in a digester that provides an anaerobic environment in which the microorganisms break down the manure and produce CH4. The CH4 is then used as a biogas and combusted into energy. The digester also turns the manure into digested fiber. The benefit of an anaerobic manure digester is that it isn’t as easily damaged as a covered lagoon, so there are fewer CH4 leaks. The major negative with the digester is that the manure’s hydrogen sulfide (H2S) content is increased a thousandfold, so that leaks are potentially very hazardous. Although H2S is not a greenhouse gas, it is extremely toxic, and in high quantities can cause death in minutes after exposure. Mixing speed, duration, and total solids are the major determinants of the quantity of H2S emitted from dairy manure (Andriamanohiarisoamanana, Sakamoto, Yamashiro, Yasui, Iwasaki, Ihara et al., 2015). To prevent health risks associated with H2S emission from dairy manure, it is recommended that the mixing speed and duration be kept as low as possible, while a total solids concentration of above 9% should be applied during the application of dairy manure (Andriamanohiarisoamanana et al., 2015).
Other practices can reduce greenhouse gas emission. A practice that helps to reduce CH4 emissions is to apply manure to soil as soon as possible. Storing manure for an extended period of time can encourage anaerobic decomposition that will result in increased CH4 production. Also, keeping manure dry and avoiding applying manure to saturated soil will reduce CH4 emission due to anaerobic decomposition. The application of manure shortly before crop or pasture growth can mitigate N2O production. Improving soil drainage and avoiding soil compaction can facilitate soil aeration, which allows the maximum amount of available nitrogen to be used by the plant, thus reducing CH4 and N2O emissions. Manure inorganic N is available to the plant immediately, but organic N requires a slower microbial process to be mineralized. The availability of dairy manure organic N is highly variable and cannot be predicted from simple compositional parameters (van Kessel & Reeves, 2002).
Intensive versus Extensive Systems
Because of the differences in a typical diet that dairy animals received in intensive versus extensive systems, the greenhouse gas emissions from these two distinct systems are perceived differently. Methane emission is generally lower in dairy cows raised in a confinement system, where they are fed more digestible diets with a higher proportion of concentrate. However, CH4 production is generally higher in the extensive system, in which dairy cows graze on pasture, because the animals are consuming higher fiber and lower digestible diets, without the consideration of carbon sequestration and nutrient recycling by plants.
The type of forages grown in the pasture can make a difference in greenhouse emissions. Perennial forages trap atmospheric CO2 in their extensive root systems, storing carbon below ground (Climate Change Connection, 2013). The plants act as small carbon sinks, removing the carbon from the air and storing it in the soil. Generally speaking, a diversity of native, deep-rooted, and productive plant species are needed for good-quality pastures. These vigorous plants ensure adequate vegetative cover to protect against erosion, are able to handle frequent grazing, and sequester atmospheric CO2 to store as carbon in their roots. These three factors lower the amount of carbon in the air in such way that pasture grazing of ruminants becomes beneficial in reducing the total greenhouse gases in the atmosphere. Integrating perennial legume forages, such as clover or alfalfa, into pasture mixes can help improve overall plant and pasture health. Therefore, mixing different types of forage can be beneficial to both the environment and the animals. Although perennial legumes can help sequester soil carbon, perennial grasses have been found to store more carbon than legumes in a pasture setting (Climate Change Connection, 2013). The plants fix carbons and provide the animal with a variety of nutrients. The carrying capacity (amount of animals a system can support) of a pasture was increased by 28% when alfalfa was grown with the grass stand (Climate Change Connection, 2013). The mixture of legume with grass facilitates plant growth through nitrogen fixation and carbon sequestration and consequently increases carrying capacity. Younger forage stands provide better nutritional values and tend to have lower CH4 emissions than more mature stands.
From a different perspective, pasture-based farming can reduce greenhouse gas emissions from the fuel used in feed harvesting and processing when animals are allowed to harvest their own feed during the summer months. This also allows the cattle to facilitate the spreading of manure, limiting the CH4 and CO2 created by manure storage. Alternating between periods of grazing and periods of rest helps maintain forage health by reducing weed competition and allowing plant recovery. This rotational grazing allows the cattle to graze on the pasture area when the forage is at the optimal stage of maturity, allowing for the best nutrient quality and reducing CH4 emissions. Cattle are selective eaters and rotational grazing encourages animals to consume all plant materials, preventing under- or overgrazed areas, and reducing wastage. Advantages of a managed grazing system include lower enteric CH4 emissions (as g/kg live weight), higher animal production/ha, and increased opportunity for high stocking rates without permanent damage to plants (Grainger & Beauchemin, 2011). Potentially, multispecies intensive grazing can offer a solution to not only reduce the greenhouse gases produced by the decomposition of manure but to help reverse the effects of global warming.
Since the Neolithic, dairy has played an important role in the evolution of human civilization, and milk and dairy products have been an essential part of the foundation for human health and nutrition ever since. Through the advancement in science and technology, the increase in production efficiency of dairy represents one of the most significant transformations in the livestock industry. In the face of increasing environmental concern and consumer expectations, dairy will continue to increase production efficiency through improvements in genetics, nutrition, and management. The goals of reducing greenhouse gas emissions from enteric methanogenesis and efficient management of animal waste are vital for the sustainability of dairy. A balance among economic returns, environmental costs, and animal welfare will continue to shape the future of the dairy industry.
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