Sire selection for profit in postweaning beef production

Abstract

The objectives of this research were to: 1) develop a model of postweaning beef production that uses growth and carcass expected progeny differences (EPD) from random regression models to predict the profitability of alternative sires; 2) evaluate expected profit outcomes and the impact on profit of not accounting for growth and carcass genetic differences when feeding progeny of alternative sires to a constant endpoint; 3) evaluate and compare profit and profit variability accounting for growth and carcass genetic differences, and the impact on expected profit of not accounting for these differences, when feeding progeny of alternative sires to an optimum endpoint; and 4) determine the impact on profit at alternative finish endpoints of single-trait selection for desirable changes in growth and carcass traits and evaluate the importance of accounting for selection when identifying finish endpoints. An object-oriented model was developed as the basis for a postweaning decision support system (DSS) to predict the daily growth and profitability of feedlot animals, based on genetic differences in growth and carcass traits, for selection of sires considering alternative finish endpoints. Simulated growth was a function of components describing nutrition, environment, management decisions, market conditions and genetics. Model parameters included average postweaning performance as designated by the user to identify the appropriate growth curve, which was then adjusted by an animal's genetic potential to obtain a prediction of growth, carcass traits, and profit. The DSS contained both deterministic and stochastic processes for flexibility in implementation. Validation indicated that the DSS appropriately accounted for differences in genetic potential, but there exists room for improvement in the prediction of marbling score throughout the feeding period. The last three project objectives were addressed by simulating performance for 16 sire genotypes in the DSS. These genotypes consisted of all possible combinations of high (H) and low (L) levels for weight (consisting of available weights - birth, weaning and yearling weight), backfat thickness, marbling score and longissimus muscle area relative to average EPD in the Red Angus sire summary. Weight EPD for a specified day on feed were calculated using a random regression approach and variance components for all traits obtained from the Red Angus analysis. Average postweaning performance was determined from literature values and other model parameters were chosen to reflect a plains/high plains commercial feedlot. Median profit and distributions of profit values (n = 1,000) were calculated for each sire genotype at a 1.1 cm constant backfat thickness (FT) and the optimum finish (OPT) endpoint (point of profit maximum). Selection for improvements in growth and carcass traits was also simulated for one sire genotype at three finish endpoints. Simulation results indicated a wide range of median profit and profit values different than would be expected considering breed or biological type averages only, suggesting that certain sire genotypes may be less profitable than expected at the FT endpoint. The results also showed that some genotypes conferred a greater probability of negative profit values compared to average. Profit increased at the OPT endpoint for all genotypes with some reduction in negative profit potential, but some sires continued to have large negative impacts on profitability. Profit also increased with selection, but not in a predictable manner and increases were not maintained with continued selection. This research illustrates the difficulty in selecting sires for maximizing profit in the postweaning phase of beef production based on EPD alone. Accounting for genetic differences concurrently with finish endpoints is necessary to correctly predict expected outcomes allowing selection for sires with the most profitable combination of traits for a given production and marketing system.