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Systems Analysis of Sources of Genetic and Environmental Variation in Efficiency of Beef Production: Heterosis and Complementarity¹

Texas Agricultural Experiment Station College Station, 77843

Abstract

Biological and economic effects of hybrid vigor and complementarity, interacting with cow size and production environment in integrated, closed beef production systems, were simulated with a comprehensive deterministic model. All systems combined two profit centers, cow-calf and feeder, and were subject to a common fixed expenditure for nutrients. Comparisons included: number of cows maintained, live weight produced, gross income, net income and return on investment. Comparisons were among systems yielding first-cross slaughter cattle from matings of straightbred sires and dams, differing genotypically for body size. The size genotypes, represented by mature cow weight, were small (430 kg), medium (500kg) and large (600 kg). Complementarity; a trait of the production unit rather than the individual; is the cumulative effect of interactions among the phenotypes of the sire, dam and produce on the phenotypes of the production system. Maximum complementarity was achieved from matings of large sire and small dam lines which yielded relatively growthy, efficient slaughter produce from a cow herd with relatively low maintenance costs. All breeding programs were replicated in two managerial-nutritional regimes: Drylot, in which relatively expensive, harvested feeds were fed to the cow herd; and Pasture, in which the cow herd grazed on relatively inexpensive pasture. The Pasture regime was consistently more profitable. Although an interaction between dam size and management regime suggested the futility of seeking a universally optimum cow size, mating systems using large bulls and relatively smaller cows were the most profitable in both regimes.

¹ This research was supported in part by the Linkletter Foundation, 2192 Dupont, Irvine, Calif. Also, contributions of G.M. Smith to the statistical definition of complementarity are acknowledged.

² Present address: Agri-Link Corp., 2192 Dupont, Irvine, Calif. 92664

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