Effect of Rate of Gain of Fattening Beef Calves on Carcass Composition

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Abstract
Four trials, involving 88 individually-fed calves, were conducted to study the effects of rapid vs. moderate rates of gain on feedlot performance, carcass composition and efficiency of fat and lean production. Rapid rates of gain were provided by grain intakes of approximately 2 lb. per 100 lb. of body weight in an otherwise balanced ration. Moderate gains were obtained when 1 lb. of grain per 100 lb. of body weight was provided plus additional roughage. In three trials calves were fed for approximately 400 lb. feedlot gain in two phases. A switch-over after 200 lb. gain was made in two groups to provide high-moderate and moderate-high comparisons. In a fourth trial high and moderate levels were compared with calves removed and slaughtered on both a time- and weight-constant basis. Detailed physical separation data were obtained on the 9-10-11th rib with chemical analyses of lean and tenderness tests. Weaner calves fed to gain rapidly for 400 lb. in the feedlot reached slaughter weight in a shorter period and required less feed per pound of gain. They produced higher grading carcasses upon slaughter with more marbling and less lean than calves fed to gain moderately. The latter produced gain with less energy supplied by grain but more energy from roughage. They also yielded significantly more lean and less fat in the carcass and were more efficient in converting feed protein to carcass lean. Little difference was evident in chemical composition of lean or in the tenderness and desirability of the final product. When calves which had gained moderately (1.3 lb. per day) were removed on a time-constant basis, they proved to be less efficient in converting energy to gain, and had much lower grading carcasses with significantly less lean and fat than those fed to gain rapidly. In addition, the l. dorsi muscle area was reduced, and marbling and tenderness were adversely affected. More rapid gains than the moderate level appeared necessary for the production of maximum lean of best quality. Reversing the plane of nutrition after 200 lb. gain from moderate to high or high to moderate resulted in efficiency and carcass composition similar to those fed at the same level throughout the fattening period. Lean and fat development during the second 200 lb. gain period appeared to be important in carcass quality and over-all efficiency of production in the growing-fattening calf. The moderate-high pattern appeared to be promising, whereas the high-moderate regime proved least desirable under the conditions of this study. Copyright © 1965. American Society of Animal Science . Copyright 1965 by American Society of Animal Science

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