Meinert T R, Pearson R E, Hoyt R S
Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061-0315.
J Dairy Sci. 1992 Aug;75(8):2254-64. doi: 10.3168/jds.S0022-0302(92)77986-7.
Individual lactation records from Holstein cows in 3449 herds participating in an AI stud's young sire sampling program from 1971 to 1987 were used to characterize the sampling program and to estimate genetic merit and trend. Average genetic merit of cows in sampling program herds was consistently superior to the average genetic merit of cows in the US population. Genetic trend of sires of first-crop cows was 58 kg of milk and 1.5 kg of fat/yr from 1971 to 1978 and 176 kg of milk and 5.5 kg of fat/yr from 1979 to 1987. The average genetic merit of sires of first-crop cows born after 1983 was equivalent to or exceeded the genetic level of sires of other cows in the herd. Within-herd-year means and standard deviations of yield, genetic evaluation, and management traits (herd-year characteristics) were computed for a subset of 341 herds contributing first-crop daughters for at least 10 yr. The average of each herd-year characteristic during 10 or more years was used to predict within-herd genetic trend. Herd characteristics explained up to 51% of differences in within-herd genetic trends. Average sire genetic merit of daughters other than first-crop daughters accounted for up to 80% of the explained differences. Other herd characteristics suggested that herds with larger within-herd standard deviation milk yields, a larger number of young sires represented, younger cows, and greater percentage of cows sired by AI sires made greater genetic improvement. Results indicated that the average genetic merit of cows and the rate of within-herd genetic improvement are higher in herds that participate in a young sire sampling program.
利用1971年至1987年参与人工授精种畜场青年公牛采样计划的3449个牛群中荷斯坦奶牛的个体泌乳记录，来描述采样计划的特征，并估计遗传价值和趋势。采样计划牛群中奶牛的平均遗传价值始终优于美国总体奶牛的平均遗传价值。1971年至1978年，头胎奶牛父亲的遗传进展为每年58千克牛奶和1.5千克脂肪；1979年至1987年，为每年176千克牛奶和5.5千克脂肪。1983年后出生的头胎奶牛父亲的平均遗传价值等于或超过了牛群中其他奶牛父亲的遗传水平。对于至少10年提供头胎女儿的341个牛群的子集，计算了产奶量、遗传评估和管理性状（牛群年度特征）的牛群年内均值和标准差。利用10年或更长时间内每个牛群年度特征的平均值来预测牛群内的遗传趋势。牛群特征解释了牛群内遗传趋势差异的51%。头胎女儿以外女儿的平均父亲遗传价值占已解释差异的80%。其他牛群特征表明，牛群内产奶量标准差较大、代表的青年公牛数量较多、奶牛较年轻以及人工授精公牛所生奶牛比例较高的牛群，遗传进展更大。结果表明，参与青年公牛采样计划的牛群中奶牛的平均遗传价值和牛群内遗传改良率更高。
