Evaluation of Residual Feed Intake in Centrally-Tested Bulls and Related Steers
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Feed intake was measured on 1433 Angus, Simmental and composite Simmental-Angus bulls at the Auburn University Beef Evaluation Center (AUBEC) from 1977 to 2007. All bulls were housed at the AUBEC for a minimum of 70 days. Bulls were trained to individual Calan Gates® within 21 days of arriving. All bulls were consigned by individual Alabama producers. Bulls were measured for weight and height either biweekly or monthly depending on year. SC and ultrasound measurements for carcass traits were taken at yearling age (330 to 400 days). Feed intake and carcass trait data from 760 Angus and Simmental-composite steers were acquired courtesy of the American Simmental Association’s (ASA) Carcass Merit Project. Residual feed intake (RFI) was determined by regressing metabolic mid-weight and ADG on intake by year of test for bulls and by contemporary group for steers. High percentage Angus bulls consumed more DM per day, had higher FCR and RFI than purebred Angus, halfbloods, high percentage Simmental and Simmental bulls. Angus steers consumed more DM per day had higher FCR and RFI than high percentage Angus steers and halfbloods. Heritability was estimated for RFI using MTDFREML in bulls (0.42±0.05) and in steers (0.20±0.05). Genetic correlations between steer and bull RFI ranged from -0.18 to 0.33 depending on covariate. Bulls and steers classified as low RFI consumed less DM per day and had more favorable FCR than medium and high RFI animals. Results indicate RFI is a moderately heritable trait and improvements within feed intake and FCR should be achievable when selection is made with RFI. However, selection of bulls based on their RFI in an attempt for them to sire more efficient steers may not be practical as the genetic relationships between steer RFI and bull RFI were variable.