Pérez-Enciso M, Foulley J L, Bodin L, Poivey J P
Station de Génétique Quantitative et Appliquée, INRA, Jouy-en-Josas, France.
J Anim Sci. 1994 Nov;72(11):2775-86. doi: 10.2527/1994.72112775x.
A bivariate threshold model for ovulation rate and embryonic survival was developed and the genetic relationships in the observed scale among ovulation rate, embryonic survival, and litter size were derived. This model was applied to data of nulliparous Lacaune sheep. Heritabilities assumed were .30, .05, and .12 for ovulation rate, embryonic survival, and litter size, respectively. Three values for genetic correlation between ovulation rate and embryonic survival were considered: -.78, -.30, and 0. Three criteria to increase litter size were studied: a linear index combining ovulation rate and embryonic survival, ovulation rate, and litter size. The linear index used gave an increasing weight to embryonic survival with higher ovulation rates. A selection scheme was simulated to test predications of response for the different criteria. A nucleus of 10 sires and 300 dams was simulated. Females were selected according to their own performance (mean of three records) and males according to their dam's performance. Selection was continued for six discrete generations. Response with an index was better than direct selection only in the short term, whereas this superiority was not maintained in the last generations of selection. Indirect selection on ovulation rate was clearly inferior to both index and direct selection. In the situation analyzed here, litter size seems to be close to the optimum 'natural index' combining ovulation rate and embryonic survival.
建立了排卵率和胚胎存活率的双变量阈值模型，并推导了排卵率、胚胎存活率和产仔数在观测尺度上的遗传关系。该模型应用于初产拉库纳绵羊的数据。假设排卵率、胚胎存活率和产仔数的遗传力分别为0.30、0.05和0.12。考虑了排卵率与胚胎存活率之间遗传相关性的三个值：-0.78、-0.30和0。研究了增加产仔数的三个标准：结合排卵率和胚胎存活率的线性指数、排卵率和产仔数。所使用的线性指数对排卵率较高时的胚胎存活给予了更大的权重。模拟了一种选择方案来测试不同标准下的反应预测。模拟了一个由10只公羊和300只母羊组成的核心群。根据母羊自身的表现（三次记录的平均值）选择母羊，根据公羊母亲的表现选择公羊。连续进行六代选择。仅在短期内，使用指数选择的反应优于直接选择，而在最后几代选择中这种优势并未保持。对排卵率进行间接选择明显不如指数选择和直接选择。在此处分析的情况下，产仔数似乎接近结合排卵率和胚胎存活率的最佳“自然指数”。
