Davis M E, Simmen R C
Department of Animal Sciences, The Ohio State University, Columbus 43210-1095, USA.
J Anim Sci. 2000 Sep;78(9):2305-13. doi: 10.2527/2000.7892305x.
Divergent selection for serum insulin-like growth factor-I (IGF-I) concentration began at the Eastern Ohio Resource Development Center (EORDC) in 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 were fed in drylot for a 140-d postweaning period. At the conclusion of the postweaning test, bulls not selected for breeding were slaughtered and carcass data were collected at a commercial abbatoir. At the time of this analysis, IGF-I measurements were available for 1,283 bull and heifer calves, and carcass data were available for 452 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 d 28, 42, and 56 of the postweaning period, and for mean IGF-I concentration were .32, .59, .31, and .42, respectively. Direct heritabilities for carcass traits ranged from .27 to 1.0, .26 to 1.0, and .23 to 1.0 when the age-, fat-, and weight-constant end points, respectively, were used, with marbling score having the smallest heritability and longissimus muscle area having the highest heritability in each case. Maternal heritability and the proportion of phenotypic variance due to permanent environmental effect of dam generally were < or = .21 for IGF-I concentrations and for carcass traits other than longissimus muscle area. Additive genetic correlations of IGF-I concentrations with backfat thickness, longissimus muscle area, hot carcass weight, marbling score, quality grade, and yield grade averaged -.26, .19, -.04, -.53, -.45, and -.27, respectively, when carcass data were adjusted to an age-constant end point. Bulls with lower IGF-I concentrations had higher marbling scores and quality grades, but also had higher backfat thickness and yield grades regardless of the slaughter end point. Serum IGF-I concentration may be a useful selection criterion when efforts are directed toward improvement of marbling scores and quality grades of beef cattle.
1989年，俄亥俄州东部资源开发中心（EORDC）开始对血清胰岛素样生长因子-I（IGF-I）浓度进行分化选择，使用了100头春季产犊（50头高系和50头低系）和100头秋季产犊（50头高系和50头低系）的纯种安格斯母牛。断奶后，公牛和小母牛犊在干栏中饲养140天的断奶后期。断奶后测试结束时，未被选作种用的公牛被屠宰，并在一家商业屠宰场收集胴体数据。在进行此次分析时，有1283头公牛和小母牛犊的IGF-I测量数据，以及452头公牛的胴体数据。使用了一组多性状、无导数、限制最大似然法（MTDFREML）计算机程序进行数据分析。断奶后第28天、42天和56天以及平均IGF-I浓度的IGF-I浓度直接遗传力估计值分别为0.32、0.59、0.31和0.42。当分别使用年龄恒定、脂肪恒定和体重恒定的终点时，胴体性状的直接遗传力范围为0.27至1.0、0.26至1.0和0.23至1.0，在每种情况下大理石花纹评分的遗传力最小，背最长肌面积的遗传力最高。对于IGF-I浓度和除背最长肌面积以外的胴体性状，母体遗传力和由于母牛永久环境效应导致的表型方差比例通常≤0.21。当将胴体数据调整到年龄恒定终点时，IGF-I浓度与背膘厚度、背最长肌面积、热胴体重、大理石花纹评分、质量等级和产量等级的加性遗传相关性平均分别为-0.26、0.19、-0.04、-0.53、-0.45和-0.27。无论屠宰终点如何，IGF-I浓度较低的公牛大理石花纹评分和质量等级较高，但背膘厚度和产量等级也较高。当致力于提高肉牛的大理石花纹评分和质量等级时，血清IGF-I浓度可能是一个有用的选择标准。
