Van Vleck L D, Gregory K E, Echternkamp S E
U.S. Department of Agriculture, Clay Center, NE 68933.
J Anim Sci. 1991 Aug;69(8):3213-9. doi: 10.2527/1991.6983213x.
Repeated measures of ovulation rate on puberal heifers should be an effective way to select for increased twinning rate. A reliable estimate of the genetic correlation between ovulation and twinning rates is needed to implement such selection and to predict its efficiency. Restricted maximum likelihood was used to estimate genetic correlations from subsets of data collected from the twinning project at the Roman L. Hruska U.S. Meat Animal Research Center. The animal model included numerator relationships among the animals and fixed effects of year-season of measurement, age at measurement, and birth group. Genetic correlations between averages of ovulation rates for three, four, five, six, seven, and eight estrous cycles and the occurrence of twins were, respectively, .62, .76, 1.00, 1.00, 1.00, and .98 based on observations on 200 to 325 puberal heifers. Corresponding phenotypic correlations ranged from .06 to .26. Genetic correlations between ovulation rate in a single estrous cycle and occurrence of twins were .38, .98, and .98, respectively, for 323, 430, and 283 cows with ovulation rate measured after measurement of twinning, in the same season as measurement of twinning, and more than 1 yr before measurement of twinning. Phenotypic correlations were .00, .07, and .00. Genetic and phenotypic correlations among ovulation rates at six consecutive estrous cycles averaged, respectively, .66 and .12 for 610 heifers. Heritabilities for ovulation rates in individual cycles averaged .16. No evidence of negative environmental covariance between ovulation rates in adjacent cycles was found. These results support the approach of indirectly selecting for twinning rate by measuring ovulation rates in estrous cycles of puberal heifers.
对青春期小母牛的排卵率进行重复测量应该是选择提高双胎率的有效方法。要实施这种选择并预测其效率，需要对排卵率和双胎率之间的遗传相关性进行可靠估计。采用限制最大似然法，根据在美国肉类动物研究中心罗马·L·赫鲁斯卡双胞胎项目收集的数据子集来估计遗传相关性。动物模型包括动物之间的亲缘关系以及测量年份季节、测量时年龄和出生组的固定效应。基于对200至325头青春期小母牛的观察，三个、四个、五个、六个、七个和八个发情周期的排卵率平均值与双胎发生之间的遗传相关性分别为0.62、0.76、1.00、1.00、1.00和0.98。相应的表型相关性在0.06至0.26之间。对于在测量双胎后、与测量双胎在同一季节以及在测量双胎前一年多测量排卵率的323头、430头和283头母牛，单个发情周期的排卵率与双胎发生之间的遗传相关性分别为0.38、0.98和0.98。表型相关性分别为0.00、0.07和0.00。610头小母牛连续六个发情周期的排卵率之间的遗传和表型相关性平均分别为0.66和0.12。各个周期排卵率的遗传力平均为0.16。未发现相邻周期排卵率之间存在负环境协方差的证据。这些结果支持通过测量青春期小母牛发情周期的排卵率来间接选择双胎率的方法。
