Comparison of calf-fed vs yearling-fed management for the estimation of carcass trait genetic parameters in Simmental cattle

Richard Gregory Tait Jr., Iowa State University


Selection indexes for feedlot performance have been developed by U.S. beef breed associations to help commercial producers with multiple trait selection decisions. The objective of this study was to evaluate the implications of backgrounding cattle after weaning on selection for feedlot profitability. Carcass data records for 11,011 animals and a three generation pedigree were obtained from the American Simmental Association database. Carcass traits of primary interest in this analysis were marbling score (MARB), 12 th rib fat thickness (CFT), 12th rib ribeye area (CREA), and hot carcass weight (HCW). Estimated post weaning gain (EPWG) was determined using weaning weight and HCW for each individual. Post-weaning management strategies of direct placement into the feedlot (Calf-Fed) or backgrounding then placement into the feedlot (Yrlg-Fed) were evaluated. When HarvestCG and percent Simmental were included as fixed effects in multiple trait models, Calf-Fed management heritability estimates for EPWG, MARB, CFT, CREA, and HCW were 0.38, 0.38, 0.46, 0.38, and 0.45, respectively. Management as Yrlg-Fed reduced heritability estimates of EPWG, MARB, CFT, CREA, and HCW by 0.25, 0.09, 0.36, 0.10, and 0.16, respectively. Expression of EPWG, MARB, CFT, CREA, and HCW had strong positive genetic correlations under Calf-Fed and Yrlg-Fed management of 0.84, 0.95, 0.85, 0.79, and 0.61, respectively. We also investigated several potential shifts to the economic environment and how these shifts would influence sire selection decisions based on the selection index for feedlot profit under Calf-Fed management. A dynamic economic sensitivity analysis was performed. The sire index rank correlation was greater than or equal to 0.872 between any of the dynamic economic shifts. Furthermore, efficiency of selection when a dynamic economic shift occurs between selection of parents and production of progeny was greater than 0.893 across all of our dynamic economic shifts. It is very likely that the same sires would be selected for profit in feedlot performance across all of our tested economic situations. Overall, the Calf-Fed management system helped to better identify genetic differences among animals for carcass traits and selection index values based on Calf-Fed management data were very robust across a multitude of economic situations.