A bioeconomic model for comparing beef cattle genotypes at their optimal economic slaughter end point.

A bioeconomic model of a feedlot was developed for the comparison of beef cattle genotypes under specified management and marketing conditions. The optimization behavior of commercial feedlot managers is incorporated into the model using optimum economic rotation theory. The days spent in the feedlot (rotation) by a group of animals are derived using this theory so as to maximize an objective function. Differences among breeds in the present value of profits from a single rotation, expressed per animal, represent the expected price premium paid for a feeder animal of a particular breed. Feed requirements and growth rates for a genotype are predicted over time for a specified diet from estimated mature size. Estimates of carcass fatness over time as a function of the energy content of the diet and estimates of dressing percentage over time are used for each genotype. A base model is described that incorporates biological parameters estimated for 11 breeds from a major breed comparison experiment and uses prices of inputs and outputs for Ontario feedlots. Sensitivity of the model to these biological and economic assumptions is shown. When breeds are compared at constant days fed, weight, or fat depth slaughter points, rankings are inconsistent, relative to those when each breed is slaughtered at its optimal economic point. The model can be used to establish appropriate slaughter end points for comparing beef cattle breeds and crosses and to evaluate breeding objectives for feedlot traits in genetic improvement programs.