Davis M E, Boyles S L, Moeller S J, Simmen R C M
Department of Animal Sciences, The Ohio State University, Columbus 43210-1095, USA.
J Anim Sci. 2003 Sep;81(9):2164-70. doi: 10.2527/2003.8192164x.
A divergent selection experiment for serum IGF-I concentration began at the Eastern Ohio Resource Development Center 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 period. Real-time ultrasound measurements of backfat thickness and longissimus muscle area were taken on d 56 and 140 of the postweaning test. Only ultrasound data from calves born from fall 1995 through spring 1999 were included in the analysis. At the time of this study, IGF-I measurements were available for 1,521 bull and heifer calves, and ultrasound data were available for 636 bull and heifer calves. Data were analyzed by multiple-trait, derivative-free, restricted maximum likelihood methods. 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 0.26 +/- 0.07, 0.32 +/- 0.08, 0.26 +/- 0.07, and 0.32 +/- 0.08, respectively. Direct heritabilities for ultrasound estimates of backfat thickness ranged from 0.17 +/- 0.11 to 0.28 +/- 0.12, whereas direct heritabilities for longissimus muscle area ranged from 0.20 +/- 0.10 to 0.36 +/- 0.12, depending on the time of measurement and the covariate used for adjustment (age vs. weight). Direct genetic correlations of IGF-I concentrations with backfat thickness at d 56 and 140 and with longissiumus muscle area at d 56 and 140 averaged 0.02, 0.20, -0.08, and 0.23, respectively, when age was used as the covariate for both IGF-I and ultrasound measurements. Corresponding genetic correlations when age was used as the covariate for IGF-I and weight was used as the covariate for ultrasound measurements were 0.05, -0.07, -0.22, and -0.04, respectively. Therefore, the positive associations of serum IGF-I concentration with backfat thickness and longissimus muscle area at d 140 seem to have been partially mediated by weight. Results of this study do not indicate strong associations of serum IGF-I concentration with fat thickness or muscling of bulls and heifers during the postweaning feedlot period.
1989年，俄亥俄州东部资源开发中心开展了一项针对血清胰岛素样生长因子-I（IGF-I）浓度的 divergent 选择实验，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，公牛犊和母牛犊在干栏中饲养140天。在断奶后测试的第56天和第140天，对背膘厚度和腰大肌面积进行实时超声测量。分析仅纳入了1995年秋季至1999年春季出生的犊牛的超声数据。在本研究时，有1521头公牛犊和母牛犊的IGF-I测量值，以及636头公牛犊和母牛犊的超声数据。数据采用多性状、无导数、限制最大似然法进行分析。断奶后第28天、42天和56天的IGF-I浓度以及平均IGF-I浓度的直接遗传力估计值分别为0.26±0.07、0.32±0.08、0.26±0.07和0.32±0.08。超声估计的背膘厚度的直接遗传力范围为0.17±0.11至0.28±0.12，而腰大肌面积的直接遗传力范围为0.20±0.10至0.36±0.12，这取决于测量时间和用于调整的协变量（年龄与体重）。当年龄用作IGF-I和超声测量的协变量时，IGF-I浓度与第56天和140天的背膘厚度以及第56天和140天的腰大肌面积的直接遗传相关性平均分别为0.02、0.20、-0.08和0.23。当年龄用作IGF-I的协变量且体重用作超声测量的协变量时，相应的遗传相关性分别为0.05、-0.07、-0.22和-0.04。因此，血清IGF-I浓度与第140天的背膘厚度和腰大肌面积之间存在的正相关似乎部分是由体重介导的。本研究结果并未表明在断奶后育肥期血清IGF-I浓度与公牛和母牛的脂肪厚度或肌肉发育之间存在强关联。
