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A system for Predicting Body Composition and Performance of Growing Cattle¹

Cornell University, Ithaca, NY 14853

Abstract

A system for summarizing and applying factors known to influence body composition and feedstuff utilization to predict performance of growing cattle is outlined. Included are adjustments for sizes, breeds and sexes, varied body conditions due to previous nutritional treatment, use of various growth stimulants, feed additives and various environments. The physiological effects of these factors are estimated using results from various experiments. Dry matter intake equations are described, as are equations to predict quality and yield grades. The maintenance requirement is a function of actual body weight (77 kcal/BW^.75), but the gain requirement is a function of the proportion of fat and protein in the tissue gain, based on an estimate of the weights at which alternative frame sizes have equivalent percentages of protein and fat (equivalent weight). Cattle of alternative beef breeds with similar frame sizes are assumed to have similar Net Energy (NE) requirements; Holsteins, however, are assumed to have 12% higher NE requirements. A scale from 1 to 7 was devised to adjust NE_maintenance (NE_m) requirements for environment, with the most severe conditions increasing NE_m requirements 30%. Use of growth stimulants increases the weight at which the percentage body fat and protein are similar to nontreated animals. Antibiotics, monensin and lasalocid increase feedstuff NE_m and NE_gain (NE_g) values 4%, 10%, and 6%, respectively. A continuous scale of 1 to 9 was devised to adjust for previous nutritional treatments. Thin body condition increases feed NE_m by 4.5% and feed NE_g by 10%, but fleshy body condition decreases feed NE_m by 4.5% and feed NE_g by 10%. Dry matter intake is assumed to be 100, 95 and 90 g/BW_kg^.75 for average frame equivalent weights of 363, 431 and 476 kg, respectively. This base is increased by 10% for yearlings and 17% for Holsteins and is decreased by 10% for monensin, 2% for lasalocid and diets above 1.27 NE_g/kg dry matter (DM). Empty body fat (EBF), carcass fat % (CF), quality grade (QG) and yield grade (YG) are estimated as follows: EBF = -.61 + .037 EBW + .00054 EBW²; CF % = .7 + 1.0815 EBF %; QG = 2.5 + .23 CF %; YG = -1.7 + .15 CF %. Tests and applications of this system, using a field useable microcomputer, are discussed.

¹ Presented at the Symposium on "Nutritional Manipulation and Interpretation of Body Compositional Differences in Growing Farm Animals," held during the 73rd Annu. Meet, of the ASAS, N. Carolina State Univ., Raleigh, July 26-29, 1981.

² Dept. of Agr. Economics, Michigan State Univ., East Lansing 48824.

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