Nutritional Effects on the Distribution of Live Weight as Gastrointestinal Tract Fill and Tissue Components in Growing Cattle

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Abstract
Live weight gain (LWG) is an indispensible measure for estimating animal performance in feeding trials and production systems. With a balanced diet, LWG at a given body weight essentially depends on energy intake. On forage-based diets, however, variations in gut fill may be so large as to render LWG almost meaningless as a standard of growth rate. Consequently, use of a constant factor to convert LWG to empty body weight gain (EBWG) will lead to erroneous results. The prediction of EBWG from LWG can be improved when average dry matter intake is taken into account. Knowledge of the carcass weight may be helpful in evaluating the evolution of the empty body for beef cattle. The concept of constancy in composition of growth implies that growth rate is proportional to energy intake above maintenance and that EBWG composition cannot be modified. However, modification of the chemical composition by nutrition has been shown in a number of recent experiments. The modifications of protein, fat, energy, ash, dry matter and water:protein ratio in the EBWG by nutrition are discussed in detail in this paper. The most significant change is an increase in the fat proportion of the EBWG with higher feeding levels, especially in early maturing breeds. This shift towards a higher fat deposition goes along with an increase in energy and dry matter concentration of the EBWG while the proportionate contribution of protein to either EBWG or energy gain is reduced. To make quantitative estimates of the effects on composition of EBWG as produced by differences in growth rate, sex and breed, two independent models have been developed. The procedures are given in the text. If data on EBWG cannot be obtained, carcass gain is a more reliable measure than LWG for estimating growth rate. An increase in energy intake will increase carcass gain as well as carcass fat percentage. The impact of variations in protein Intake on carcass meat production needs further examination. Copyright © 1984. American Society of Animal Science. Copyright 1984 by American Society of Animal Science.

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