Testing purebred and commercial combined selection in Angus: Tri-County Steer Carcass Futurity
Leachman, Lance Douglas
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The objective of this study was to characterize genetic relationships between growth and carcass traits measured in commercial feedlot and purebred cattle that would aid in determining the effectiveness of combined crossbred and purebred selection (CCPS) strategies for sire selection. Data included 2,183 steers and 418 heifers enrolled in the Tri-County Steer Carcass Futurity (TC). Feedlot traits evaluated were initial body weight at time of delivery (IBW) and final BW at time of harvest (FBW) and carcass backfat thickness at the 12th rib (CFAT), marbling score at the 12th rib (CMAR) and ribeye area at the12th rib (CREA). Purebred data from the American Angus Association (AAA) included records of 139,602 bulls, 130,944 heifers and 6,656 steers for weaning weight (WW); 85,702 bulls, 76,603 heifers and 1,908 steers for yearling weight (YW); and 62,752 bulls and 45,958 heifers for ultrasound measures of backfat thickness at the 12th rib (UFAT), intramuscular fat percentage at the 12th rib (UMAR) and ribeye area at the 12th rib (UREA). The genetic correlations between IBW and WW, FBW and YW, CFAT and UFAT, CMAR and UMAR, and CREA and UREA were 0.01 ° 0.21, 0.43 ° 0.22, 0.66 ° 0.19, 0.65 ° 0.17, and 0.92 ° 0.12, respectively. Regressions of TC traits on corresponding sire EPD resulted in coefficients of 0.23 ° 0.19, 0.57 ° 0.16, 0.67 ° 0.19, 93.3 ° 12.3, and 1.08 ° 0.17 for IBW, FBW, CFAT, CMAR, and CREA, respectively. Three selection indices were evaluated on the basis of relative efficiency of genetic progress toward TC goal traits. The index including AAA records on an individual sire with TC records on his progeny was most effective, thus indicating the benefit of CCPS.
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