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Symposium: Re-Evaluation of Nutrient Allowances for High-Producing Cows

Energy Metabolism Results with Lactating Dairy Cows

Animal Husbandry Research Division, USDA, Beltsville, Maryland

ABSTRACT

Energy metabolism studies are particularly important in evaluating the energy requirements of lactating dairy cows, because they provide a quantitative measure of the extent to which the cows are utilizing body fat as an energy source or are depositing body tissue while lactating. High-producing lactating dairy cows have an immense eapacity for mobilizing body fat, and these body composition changes can occur without being accurately reflected in body weight changes. Failure to take these tissue changes into account can lead to gross misinterpretation of feed input-milk output experiments. This is especially true in the high-producing cow, which is producing 60–90 lb milk daily during the peak of lactation. During this time feed intakes are often not sufficient to meet energy requirements, but body tissue losses may not be evident because of increases in daily intakes of feed and water or retention of body water when fat is mobilized.

It has been frequently stated that additional information on the factors affecting the efficiency of utilization of energy by lactating dairy cows is needed, but only a limited number of complete energy balance experiments with lactating cows have been conducted.

¹ The assistance of Dr. P. W. Moe in summarizing and checking the data, and of Mr. Asmund Ekern, Vollebekk, Norway, in assisting with the literature summarization is gratefully acknowledged. The Beltsville studies were conducted by the Energy Metabolism Laboratory staff, including Mrs. B. D. Owens, and K. A. Barnes, O. Bowman, F. Sweeney, I. Fiscus, L. D. England, and W. C. Marcus; their assistance is gratefully acknowledged.

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