Caloric Equivalent of Live Weight Loss of Dairy Cattle

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Abstract
Two methods were used to investigate the caloric equivalent of live weight loss during undernutrition of first-lactation Holstein heifers. In one case estimates were made from a comparative slaughter trial and in the other from a carbon-nitrogen [C-N] balance trial. Feed intakes were restricted by using rations calculated to provide 65% of the minimum TDN requirements of the heifers. The comparative slaughter experiment was conducted with 17 lactating heifers. Initial mean body composition was estimated from the carcasses of 6 representative heifers slaughtered at the beginning of the trial. After 49 days on the restricted ration, 6 more heifers were slaughtered. The remaining 5 were slaughtered after a total of 105 days on the restricted ration. Body composition of all heifers was predicted from the specific gravity of the carcasses. The six heifers slaughtered after 49 days on the restricted ration were subjected to a C - N balance trial from the 41st to the 46th day of the restriction period. The caloric equivalents calculated from the comparative slaughter trials were 2,146 and 2,353 kilo-calories (kcal) per pound of weight loss in the 49- and 105-day restriction periods, respectively. The value estimated from the C - N balance was 2,393 kcal/lb. The weighted mean from the comparative slaughter trials, 2,266 kcal/lb, was considered to be a reliable estimate of energy equivalent of live weight loss over an extended period of time.