Van Vleck L D, Gregory K E
Roman L. Hruska U.S. Meat Animal Research Center, USDA, ARS, Lincoln, NE 68583-0908, USA.
J Anim Sci. 1996 Mar;74(3):522-8.
A selection experiment was established in 1981 to increase twinning rate in cattle. Results reported are through 1993 calf crops. Estimates of genetic parameters for a two-trait twinning and ovulation rate model with genetic groups were as follows: heritabilities of .03 for twinning and .07 for ovulation rates with a genetic correlation of nearly 1.00 and fractional permanent environmental variances of .06 for twinning and .05 for ovulation rate. Corresponding estimates when group effects were ignored were as follows: heritabilities of .08 and .08 and fractional permanent environmental variances of .02 and .04 for twinning and ovulation rates, respectively. Twinning rate (percentage) in the project at the U.S. Meat Animal Research Center has increased in all cows born in the project by year of calving from 3.4% in 1982 to 28.5% in 1993, a phenotypic increase of 25.1%. The estimated genetic change in twinning of cows by year of calving using the groups model has been 15.2%. The increase in average genetic value by year of birth has been 18.2% in twinning and 15.0% in ovulation rate from 1980 through 1991. Solutions for seven selected groups of foundation animals ranged from -6.0 to 33.1% and influenced genetic trend.
1981年开展了一项选择试验，以提高牛的双胎率。报告的结果涵盖了1993年以前出生的犊牛。对具有遗传群体的双胎和排卵率两性状模型的遗传参数估计如下：双胎率的遗传力为0.03，排卵率的遗传力为0.07，遗传相关接近1.00，双胎率的永久环境方差分量为0.06，排卵率的为0.05。忽略群体效应时的相应估计如下：双胎率和排卵率的遗传力分别为0.08和0.08，永久环境方差分量分别为0.02和0.04。在美国肉类动物研究中心的该项目中，按产犊年份统计，所有项目内出生母牛的双胎率（百分比）已从1982年的3.4%增至1993年的28.5%，表型增幅为25.1%。使用群体模型按产犊年份估计的母牛双胎遗传变化为15.2%。从1980年到1991年，按出生年份计算，双胎率的平均遗传值增幅为18.2%，排卵率为15.0%。七个选定基础动物群体的解范围为-6.0%至33.1%，并影响了遗传趋势。
