Selection Objective for Improving Efficiency of Beef Cattle

Simulation studies based on 1000 cows were used to evaluate biological and economic efficiency of level of milk production and two production systems, and to estimate economic values for a breeding objective and selection indexes for beef cattle. Published data were used as information for this study. Average 10-yr prices, reproduction, survival, growth, carcass characteristics, and genetic parameters from journal papers were used in the simulations. In the first study, low (L), medium (M), and high (H) milk production cows, and calf-fed and yearling systems, were analyzed. Biological and economic efficiencies were estimated for weaning and slaughter endpoints. In the second study, economic values for a breeding objective based on eleven traits and selection indexes using reported estimated breeding values were estimated for a total production system. Biological efficiencies were 29.77, 27.29, and 27.39 g weaning weight and 21.76, 19.92, and 19.81 g carcass weight per Mcal for L, M, and H cattle, respectively. Economic efficiencies (%) to weaning and to slaughter were 98.9, 94.2, and 94.6 and 105.8, 99.0, and 98.8 for L, M, and H cattle, respectively. Economic values and relative economic values ($/genetic SD) for milk production, average postweaning daily gain (ADG), mature weight, dressing percentage, rib fat thickness (FAT), kidney-pelvic-heart fat, ribeye area (REA,), marbling score (MS), calving difficulty, heifer pregnancy (HP), and gestation length were -0.046 $/kg.205 d-1 and -9.068; 56.195 ($/kg·d-1) and 4.957; -0.207 ($/kg) and -7.042; 1.970 ($/%) and 2.065; -39.285 ($/cm) and -6.904; -7.944 ($/%) and -2.401; 2.044 ($/cm2) and 9.311; 21.974 ($/score unit) and 11.023; -0.168 ($/%) and -4.095; 0.092 ($/%) and 1.633; and -1.177 ($/d) and -3.155, respectively. The selection index with greatest correlation with the breeding objective included ADG, FAT, REA, MS, HP, birth weight (BWT, kg), yearling height (cm), and maternal weaning weight (WWM, kg) with index weights of 128, -53.0, 1.92, 25.3, 0.08, -3.52, -2.39, -0.72, respectively. Characteristics consistently included in an index, in order of importance, were MS, WWM, yearling weight, and BWT. Advisor: Merlyn K. Nielse