Contributors Paul J. Weimer U.S. Dairy Forage Research Center, Agricultural Research Service, U.S. Department of Agriculture, and Department of Bacteriology, Uni- versity of Wisconsin-Madison, Madison, Wisconsin w.L. Wendorff Department of Food Science, University of Wisconsin- Madison. Madison. Wisconsin Charles H. White Department of Food Science and Technology, Mississippi State University, Mississippi State, Mississippi
Contributors xiii Paul J. Weimer U.S. Dairy Forage Research Center, Agricultural Research Service, U.S. Department of Agriculture, and Department of Bacteriology, University of Wisconsin–Madison, Madison, Wisconsin W. L. Wendorff Department of Food Science, University of Wisconsin– Madison, Madison, Wisconsin Charles H. White Department of Food Science and Technology, Mississippi State University, Mississippi State, Mississippi
Microbiology of the Dairy Animal Paul j. weimer U.S. Department of Agriculture and University of Wisconsin-Madison Madison, Wisconsin . INTRODUCTION Domestication of ruminant animals and their use to produce milk, meat, wool nd hides represents one of the cornerstone achievements in the history of ag riculture. The essential feature of the ruminant animal that has fostered its utility as a dairy animal is the presence of a large pregastric chamber where microbial digestion of feed(particularly fibrous feeds not directly digesti ble by humans) provides various fermentation products that serve as precur- sors for efficient and voluminous synthesis of milk. Without this symbiosis between animal and microbe, the dairy industry would not have developed and indeed human culture would be vastly different in its food-gathering methods The dairy animal is a host to a wide variety of microorganisms. Most of these are microbes in the digestive tract that are essential for fermentative diges tion of the animals feed. however a number of other bacteria. fungi and viruses can induce a pathogenic state in various organ systems resulting in fatal or nonfa- tal diseases. This chapter will focus first upon the microbiology of digestion by the normal flora and its occasional alteration by opportunistic microbes. This wil be followed by a brief overview of the major infectious diseases and their effects on the animal and on the quantity and quality of milk produced. Most of the information presented has been obtained from research with cows, but much of it applies to sheep and goats as well
1 Microbiology of the Dairy Animal Paul J. Weimer U.S. Department of Agriculture and University of Wisconsin–Madison Madison, Wisconsin I. INTRODUCTION Domestication of ruminant animals and their use to produce milk, meat, wool, and hides represents one of the cornerstone achievements in the history of agriculture. The essential feature of the ruminant animal that has fostered its utility as a dairy animal is the presence of a large pregastric chamber where microbial digestion of feed (particularly fibrous feeds not directly digestible by humans) provides various fermentation products that serve as precursors for efficient and voluminous synthesis of milk. Without this symbiosis between animal and microbe, the dairy industry would not have developed, and indeed human culture would be vastly different in its food-gathering methods. The dairy animal is a host to a wide variety of microorganisms. Most of these are microbes in the digestive tract that are essential for fermentative digestion of the animal’s feed. However, a number of other bacteria, fungi, and viruses can induce a pathogenic state in various organ systems resulting in fatal or nonfatal diseases. This chapter will focus first upon the microbiology of digestion by the normal flora and its occasional alteration by opportunistic microbes. This will be followed by a brief overview of the major infectious diseases and their effects on the animal and on the quantity and quality of milk produced. Most of the information presented has been obtained from research with cows, but much of it applies to sheep and goats as well. 1
Weimer IL. THE DAIRY ANIMAL A. Populations and Production There are nearly three billion domestic ruminants in the world, the most numerous and economically important of which are cattle, sheep, goats, and buffalo table Lactating dairy cattle(not including replacement heifers and dry cows)repre sent nearly one-fifth of the world's domestic cattle population and provide most of the worlds milk supply. The numbers of sheep and goats actually used for milk production are difficult to estimate, but these species are of major importance in providing protein and energy to the human populations of developing countries and fill niche markets for specialty foods in developed countries. Both sheep and goats are regarded as superior to cattle in poor-quality grazing and browsing environments, in part because of more efficient retention of water and nitrogen (Devendra and Coop, 1982). Several other ruminant animal species(water buf- falo, yak, camel, reindeer, and even the nonruminant horse)normally used in some cultures as sources of meat, hides, hair, or draft power are also milked for human consumption Because of their large size and abundant milk production, the Holstein is the predominant breed of dairy cow in use today. Improvements in animal breed ing and genetics have yielded substantially larger animals over the years(Fig. 1)with corresponding increases in feed intake. This factor, combined with a gradual shift to diets having higher energy contents (i.e, higher proportions of grain) has resulted in a progressive increase in average milk production per cow, hich in well-bred and well-managed herds may approach 13, 600 kg(approxi- mately 30,000 Ib)per lactation. Dairy cows are usually maintained on a 305-day lactation schedule, after which the cow is"dried(by reducing feed and by not milking) for 2 months before calving to permit full development of the calf and to allow the buildup of body reserves necessary for the next lactation. After calving, milk production Table 1 Worldwide Population of Domestic Ruminants and Worldwide milk Production. 1998 platon Milk production (10°head) (10° metric tons Cattle 1318 Dairy cattle 466.3 Goats 700 12.2 Buffalo 162 574 Source: Food and Agricultural Organization, 1999
2 Weimer II. THE DAIRY ANIMAL A. Populations and Production There are nearly three billion domestic ruminants in the world, the most numerous and economically important of which are cattle, sheep, goats, and buffalo (Table 1). Lactating dairy cattle (not including replacement heifers and dry cows) represent nearly one-fifth of the world’s domestic cattle population and provide most of the world’s milk supply. The numbers of sheep and goats actually used for milk production are difficult to estimate, but these species are of major importance in providing protein and energy to the human populations of developing countries and fill niche markets for specialty foods in developed countries. Both sheep and goats are regarded as superior to cattle in poor-quality grazing and browsing environments, in part because of more efficient retention of water and nitrogen (Devendra and Coop, 1982). Several other ruminant animal species (water buffalo, yak, camel, reindeer, and even the nonruminant horse) normally used in some cultures as sources of meat, hides, hair, or draft power are also milked for human consumption. Because of their large size and abundant milk production, the Holstein is the predominant breed of dairy cow in use today. Improvements in animal breeding and genetics have yielded substantially larger animals over the years (Fig. 1) with corresponding increases in feed intake. This factor, combined with a gradual shift to diets having higher energy contents (i.e., higher proportions of grain) has resulted in a progressive increase in average milk production per cow, which in well-bred and well-managed herds may approach 13,600 kg (approximately 30,000 lb) per lactation. Dairy cows are usually maintained on a 305-day lactation schedule, after which the cow is ‘‘dried’’ (by reducing feed and by not milking) for 2 months before calving to permit full development of the calf and to allow the buildup of body reserves necessary for the next lactation. After calving, milk production Table 1 Worldwide Population of Domestic Ruminants and Worldwide Milk Production, 1998a Population Milk production Species (106 head) (106 metric tons) Cattle 1318 Dairy cattle 230 466.3 Sheep 1061 8.2 Goats 700 12.2 Buffalo 162 57.4 a Source: Food and Agricultural Organization, 1999
Microbiology of the Dairy Animal A 1935 1975 B 1935 1955 1975 995 Y Figure 1 The gradual increase in annual milk production in the United States(Panel A)has been accomplished with a declining number of cows having an increasing average milk production(Panel B)
Microbiology of the Dairy Animal 3 Figure 1 The gradual increase in annual milk production in the United States (Panel A) has been accomplished with a declining number of cows having an increasing average milk production (Panel B)
Weimer steadily increases over a 6-to 8-week period and then slowly decreases for the rest of the lactation. Normally, the cow is bred again at 11-12 weeks after calv ing, and delivers her next calf some 40 weeks later. Thus, the cow is pregnant for the bulk of her lactation B. Organization of the Digestive Tract The rumen is the first of the four preintestinal digestive chambers in ruminant animals and is physically proximate to the second chamber, the reticulum(Fig 2). Because of their location and their similar function, the physiology and micro- biology of the rumen and reticulum are usually considered together. At birth, the ruminant is essentially a monogastric animal having a functional abomasum that digests a liquid diet(colostrum and milk) high in protein(Van Soest, 1994). As solids and fiber are gradually introduced into the diet, the other three preintestinal chambers develop over a period of approximately 7 weeks. The rumen is a large organ(approximately 10 L in sheep and goats but up to 150 L in high-producing dairy cows) that together with the reticulum constitute about 85% of the stomach capacity and contains digesta having 10-12% of the animal,s weight( Bryar 1970). In the rumen, microbial fermentation converts feed components into a mixture of volatile fatty acids (VFAs)acetate, propionate, and butyrate(For the sake of brevity, these and other organic acids will be referred to in this chapter as their anionic forms, although they are normally metabolized and transported across the cell membrane in their protonated(uncharged) form. An exception is made in the discussion of lactic acidosis(see IV D 1), where the acid itself is Esophagus Rumen Omasum com/u Figure 2 Schematic representation of the arrangement of the four preintestinal digestive chambers in the ruminant and illustrating the dominant size of the rumen
4 Weimer steadily increases over a 6- to 8-week period and then slowly decreases for the rest of the lactation. Normally, the cow is bred again at 11–12 weeks after calving, and delivers her next calf some 40 weeks later. Thus, the cow is pregnant for the bulk of her lactation. B. Organization of the Digestive Tract The rumen is the first of the four preintestinal digestive chambers in ruminant animals and is physically proximate to the second chamber, the reticulum (Fig. 2). Because of their location and their similar function, the physiology and microbiology of the rumen and reticulum are usually considered together. At birth, the ruminant is essentially a monogastric animal having a functional abomasum that digests a liquid diet (colostrum and milk) high in protein (Van Soest, 1994). As solids and fiber are gradually introduced into the diet, the other three preintestinal chambers develop over a period of approximately 7 weeks. The rumen is a large organ (approximately 10 L in sheep and goats but up to 150 L in high-producing dairy cows) that together with the reticulum constitute about 85% of the stomach capacity and contains digesta having 10–12% of the animal’s weight (Bryant, 1970). In the rumen, microbial fermentation converts feed components into a mixture of volatile fatty acids (VFAs)—acetate, propionate, and butyrate (For the sake of brevity, these and other organic acids will be referred to in this chapter as their anionic forms, although they are normally metabolized and transported across the cell membrane in their protonated (uncharged) form. An exception is made in the discussion of lactic acidosis (see IV.D.1), where the acid itself is Figure 2 Schematic representation of the arrangement of the four preintestinal digestive chambers in the ruminant and illustrating the dominant size of the rumen