Systems Analysis of Sources of Genetic and Environmental Variation in Efficiency of Beef Production: Cow Size and Herd Management

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Abstract
Data on Angus, Charolais, Hereford and Jersey cows and their progeny from Texas A&M University Agricultural Research Center at McGregor, supplemented with estimates of genetic and phenotypic parameters from other research, provided the basis for a deterministic model designed to examine effects of genetic variation on net economic efficiency of beef breeding systems. Herds of small, medium and large size straightbreds with mature cow weights of 430, 500 and 600 kg, respectively, were compared in vertically integrated systems under two managerial regimes. The model included nutritional costs, fixed costs, cow size and correlated progeny growth, attrition rates, milk yield for cows of different ages and other considerations. Systems utilizing small cows produced more live weight and gross income but were also more expensive to operate than systems using larger cows. In a Drylot Regime, where the expense of cow nutrition was relatively high, the increased income from small cows was more than offset by increased expenses so that systems using large cows were more profitable. However, under a Pasture Regime, where cows were maintained more cheaply, systems utilizing small cows were more profitable. Simulation of production systems provides a method of simultaneous consideration of many more factors than could feasibly be included in one experiment and may be a realistic method of developing or testing recommendations concerning optimal cow size. Copyright © 1975. American Society of Animal Science . Copyright 1975 by American Society of Animal Science.

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