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Department of Animal Science, Cornell University, Ithaca, New York 14850
ABSTRACT
In heifers of dairy breeds and ranging in age from 1 day to 14 months, weights of body protein and fat and the amount of body energy increased linearly with increasing empty-body weight. That the variation in the respective relationships is small is indicated by the r2 of 0.997, 0.961, and 0.985. The rate of change in body energy per kilogram of empty-body weight was 2.55 Meal. Although the data examined represent animals with a variety of nutritional histories, much further study is needed to determine the degree to which relationships between the body components and body weight will resist nutritional alteration.
In dairy cows 28 months to 15 years of age, relationships between body components and body weight were quite variable, reflecting the mobility of body fat, water, and protein. Although these relationships have no predictive value, they suggest general trends such as the overall rate of change of 4.38 Meal, of energy per kilogram of empty-body weight.
Composition and energy value of the body tissue gain or loss by cattle are variable. Energy equivalence values (Meal per kg) derived from various studies with cows range from 4.8 to 9.4 for body gain and from 6.3 to 7.9 for body loss. It appears possible that body tissue gain or loss could range from as much as 100% of water to about 90% of fat.
Increasing degrees of body fatness in ruminants are associated with decreasing intakes of feed. The mechanism by which fatness influences appetite is not known. However, it is possible that the accumulation of fat in the abdominal cavity, in a manner similar to that of the developing gravid uterus, might restrict gastrointestinal capacity to curtail appetite, especially when high-forage diets are ingested. Present information suggests that the intake of high-concentrate diets is regulated by other or additional means. It has been proposed that body fat depots of fat animals may release substances that depress appetite or that the adipose tissue of thin cows may utilize some unknown products of digestion at a greater rate than does the adipose tissue of fat cows to increase intake by thin cows.
In fat ruminants, digestibility of energy may be depressed at a lower intake of feed than it is in thin ones, as the level of intake increases. Whether the energy requirement for maintenance is influenced by body fatness in cattle is unsettled; in sheep, the maintenance requirement does not appear to be different for fat and thin animals. for body gain, the net utilization of the metabolizable energy ingested above maintenance appears unaffected by the degree of fatness in ruminants of the same sex. Additional study is needed to determine the effect of body fatness on the energy requirement of maintenance in cattle, especially in the lactating cow.
1 Some of the authors' investigations reported here were supported by Research Grant AM-02889 from the National Institute of Arthritis and Metabolic Diseases, U.S. Public Health Service, Bethesda, Maryland.
2 Present address: Unilever Research Laboratory, Colworth House, Sharnbrook, Bedfordshire, England.
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  U. J. Schroder and R. Staufenbiel Invited Review: Methods to Determine Body Fat Reserves in the Dairy Cow with Special Regard to Ultrasonographic Measurement of Backfat Thickness J Dairy Sci, January 1, 2006; 89(1): 1 - 14. [Abstract] [Full Text] [PDF]
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