M. E. Davis* 1,
R. C. M. Simmen+
*The Ohio State University Department of Animal Sciences
+University of Florida Department of Animal Science
Divergent selection for blood serum insulin-like growth factor I (IGF-I) concentration has been ongoing at the Eastern Ohio Resource Development Center (EORDC) since 1989 using 100 spring-calving (50 high line and 50 low line) and 100 fall-calving (50 high line and 50 low line) purebred Angus cows. Following weaning, bull and heifer calves are fed in drylot for a 140-day postweaning period. At the conclusion of the postweaning period, bulls not selected for breeding are slaughtered and carcass data are collected at a commercial packing plant. At the time of this analysis, IGF-I measurements were available for 945 bull and heifer calves, and carcass data were available for 343 bulls. A set of Multiple Trait, Derivative-Free, Restricted Maximum Likelihood (MTDFREML) computer programs were used for data analysis. Estimates of direct heritability for IGF-I concentration at days 28, 42, and 56 of the postweaning period, and for mean IGF-I concentration were 0.42, 0.73, 0.42, and 0.50, respectively. Direct heritabilities for carcass traits ranged from 0.25 (for marbling score) to 0.59 (for yield grade). Maternal heritability and the proportion of phenotypic variance due to permanent environmental effect of dam were small (i.e., < .22) for IGF-I concentrations and for carcass traits. Additive genetic correlations of IGF-I concentrations averaged backfat thickness, -0.20; ribeye area, 0.04; kidney, pelvic, and heart fat percentage (KPH), -0.99; hot carcass weight, 0.31; marbling score, 0.33; quality grade, -0.06; and yield grade, -0.06. Therefore, bulls with higher blood serum IGF-I concentrations had heavier carcasses, along with lower backfat thickness and KPH, but higher marbling scores and quality grades. Serum IGF-I concentration may be a useful selection criterion when efforts are directed toward improvement of carcass characteristics of beef cattle.
1For more information contact at: The Ohio State University, 221 Plumb Hall, 2027 Coffey Road, Columbus, OH, 43210; 614-292-4984; fax: 614-292-2929; e-mail: davis.28@osu.edu