Systems Analysis of Sources of Genetic and Environmental Variation in Efficiency of Beef Production: Mating Plans

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Abstract
The net effects of heterosis, complementarity and size on production efficiency in closed, self-contained herds employing two-breed, rotational and three-breed crossing systems were evaluated by use of simulation. Genetic, nutritional, economic and other parameters used were taken from research results, literature and intuition. The advantages and disadvantages of each crossbreeding system tended to counterbalance and equalize efficiency, but there were differences. Both heterosis and complementarity consistently added to net efficiency, but the effect of size varied between two nutritional-management systems. Crossing systems using smaller (S) cattle (430 kg mature cow weight) produced more live weight but, when nutrients for cows were relatively expensive, were less profitable than larger (L) cattle (600 kg). Single crosses were always more profitable than M size (500 kg) straightbreds except where S sires were mated to L cows. Live weight produced by single crosses was less than straightbred M in every case L cows were used. Two-breed crisscrosses were similar to single crosses in all measures of efficiency; single crosses utilizing complementarity did exceed the most efficient crisscross where complementarity can not be exploited. Three-breed crosses using L sires on either two-breed F1 or crisscross cows added an additional increment of efficiency. These results indicate that different breeds of different but uniform size for nonrotational crossing and of optimal size for rotational crossing are a useful genetic resource. Copyright © 1975. American Society of Animal Science . Copyright 1975 by American Society of Animal Science.

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