EFFECTS OF REPRODUCTIVE PERFORMANCE AND MATING SYSTEM ON FARM GROSS MARGINS IN BEEF PRODUCTION

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Abstract
A linear programming model for beef production was used to examine the effects of straightbreeding, three-breed rotational and terminal crossbreeding systems on farm gross margins at each of three reproductive rates. Terminal crossing systems that maintained a similar distribution of livestock classes in the herd as in rotational crosses (TM) and that fed all terminal cross heifers in the feedlot (T7) were examined. A farm level model was used, incorporating cows, replacement breeding females, feedlot steers and heifers and cropping with their requirements for labor and capital. In both terminal crossing systems replacement breeding females were purchased at 7 mo of age. Several combinations of the following four factors were considered: cow weights, estimates of heterosis, limitations on farm resources and prices of beef relative to feed. Calf crop percentages ranged from 68.4 to 89.7% for various combinations of reproductive rate and mating system. Higher reproductive rates produced higher farm gross margins from straightbreeding, rotational and TM terminal crosses, but the size of the increase depended on the particular combination of the four factors considered. The effect of reproduction was inconsistent for the T7 terminal crossing system, probably due to changes in age distribution of females. Compared with rotational crosses, farm gross margins for TM terminal crosses were little different when no complementarity for size was considered (< 1.0%), although superior on the average. When the terminal cross calves were sired by larger bulls mated to smaller cows, the TM system produced larger farm gross margins than the rotational system (17% on average). At the livestock prices used, T7 produced larger farm gross margins than TM due to a more complete use of farm resources, differences ranging from $4,985 to $11,660 relative to farm gross margins for TM of $14,954 and $13,401, respectively. Increases in sizes of cows in the rotational crossing and straightbreeding systems and of both sire and dam in the T7 terminal crossing system produced higher farm gross margins. Changes in estimates of heterosis used, beef to feed price ratios and farm resource situations did not in general produce changes in rankings of the mating systems. Interactions were, however, found for some particular combinations of reproductive rate, farm resources and beef to feed price ratios.