Application of a beef cattle production model to the evaluation of genetic selection criteria

Abstract

A model was developed for simulating beef cattle production under a wide range of management achemes and environments with a wide range of cattle genotypes for size, growth, and milk production. Genotypes are specified as potential levels of performances, that are reached only if a plane of nutrition is adequate. Forage intake is simulated as a function of the size and physiological status of the animals and the availability, digestibility, and crude protein content of the forage. Animal performance is calculated from the nutrient intake and the animals' condition and genetic potential. The primary consideration in developing the equations representing animal performance was to accurately describe the biological processes. Most coefficients and exponents were programmed as variables; if other values are determined to be more accurate or applicable, changes in the model can be made rather easily. Production was simulated for various genotypes of cattle, for size and milk production for three combinations of environments and breeding seasons. The environments were assumed to represent Central Texas conditions. Production efficiency was defined as the ratio of total weight of cattle sold to total weight of dry matter consumed by the entire hers; the herd included slaughter animals and all replacement females were raised in the herd. Nutritional requirements for herd bulls were not considered.