Ruminants rumen

FIGURE 7.28 Giraffes, cattle, deer, and camels are rmninant animals that are able to metabolize cellulose, thanks to bacterial celln-lase in the rumen, a large first compartment in the stomach of a ruminant. 

Small amounts of trans-unsamrated fatty acids are found in ruminant fat (eg, butter fat has 2-7%), where they arise from the action of microorganisms in the rumen, but the main source in the human diet is from partially hydrogenated vegetable oils (eg, margarine). Trans fatty acids compete with essential fatty acids and may exacerbate essential fatty acid deficiency. Moreover, they are strucmrally similar to samrated fatty acids (Chapter 14) and have comparable effects in the promotion of hypercholesterolemia and atherosclerosis (Chapter 26). 

Menke KH, Raab L, Salewski A, Steingass H, Fritz D, Schneider W. The estimation of the digestibility and metabolizable energy content of ruminant feeding stuffs from the gas production when they are incubated with rumen liquor. Journal of Agricultural Science. 1979 93 217-222. 

The requirements of dairy cattle for B-vitamins, determined almost half a century ago, concluded that a ruminant animal does not require an exogenous supply of B-vitamins because its rumen microflora should synthesise enough of these compounds to avoid deficiency. Since then, dairy cows have greatly increased their average milk and milk component yields. More recent studies have shown that B-vitamin supply in dairy cows is increased by supplementation, although losses in the rumen are extensive (Santschi et al., 2005). Whilst there are few reports of B-vitamin supplementation affecting milk quality, supplemental biotin has been shown to directly improve milk yield (Majee et al., 2003). 

The rumen is a unique specialized organ that allows ruminants to obtain energy by degrading high-fiber plant materials via a complex microbial... 

Vernon, R.G. (1981). Eipid metabolism in the rumen. In Lipid Metabolism in the Adipose Tissue of Ruminant Animals, ed. Christie, W.W., Pergamon, Oxford, pp. 279-362. 

Leucaena spp. contain mimosine, which is degraded to 3-hydroxy-4(l//)-pyridone (3,4-DHP see Section 2.2.4 for more detail). Leucaena, while toxic to unadapted ruminants, is a good source of protein and minerals for many livestock species in some countries. However, if Leucaena is ingested as 50% or more of the diet it will depress growth, cause hair loss, and reduce reproductive performance. Mimosine is a toxin that animals may become adapted to. Ruminal adaptation can be transferred from animal to animal, suggesting a specific set of rumen organisms are capable of detoxifying this amine. 

Some of the unsaturated fats ingested by ruminants are partially hydrogenated by bacteria in the rumen. In consequence, milk fat, dairy products, as well as beef and mutton fat, also contain small amounts of trans isomers, about 2 to 9%. However, in fat from ruminants the main trans fatty acid is vaccenic (18 1 t 11), while in hydrogenated fats it is elaidic (18 1 t 9) (Figure 13.14). 

The contents of the rumen pass steadily into the third chamber of the ruminant stomach , the omasum, where the fatty acids, together with water and salts, are absorbed. These fatty acids provide much of the energy for the ruminant but a price is paid virtually all the carbohydrate in the diet is fermented and almost none enters the body. Consequently, glucose must be synthesised to provide lactose in the lactating animals. The lactic and propionic acids are the precursors for the glucose (Chapter 6). It is unclear if some of this glucose is used by the brain of the ruminant. 

Finally, the contents of the omasum, now a thick slurry of microorganisms, pass into the abomasum into which are secreted acid and proteinases to produce an environment corresponding to that of the human stomach. Some of the microflora passing from the rumen to the omasum die and are digested by the acid and the enzymes. This provides the ruminant not only with an additional energy source but with vitamins and essential amino acids that its own tissues caimot synthesise. 

In ruminants, lactic and propionic acids are the major precursors of glucose. This is particularly important during lactation, since all the carbohydrate in die food is fermented by die bacteria in the rumen, so diat no glucose enters the body but glucose is required for die formation of lactose for the milk (Chapter 6). 

One product of the rumen fermentation, methane, is of no value to the ruminant. The major fermentation products used by the ruminant are the short-chain fatty acids, acetate, butyrate and propionate. Acetate and butyrate can be used for energy, but propionate is most useful for the synthesis of protein. If the fermentation could be shifted to reduce methane, acetate and butyrate production and to increase the propionate, the feed efficiency and growth rate could improved. 

Aguiar, R. and Wink, M. 2005. Do naive ruminants degrade alkaloids in the rumen Journal of Chemical Ecology, 31 4 761-787. 

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