Imbayarwo-Chikosi V E, Ducrocq V, Banga C B, Halimani T E, van Wyk J B, Maiwashe A, Dzama K
Department of Animal Sciences, University of Stellenbosch, Matieland, South Africa.
Department of Animal Science, University of Zimbabwe, Harare, Zimbabwe.
J Anim Breed Genet. 2017 Oct;134(5):364-372. doi: 10.1111/jbg.12264. Epub 2017 Mar 14.
Non-genetic factors influencing functional longevity and the heritability of the trait were estimated in South African Holsteins using a piecewise Weibull proportional hazards model. Data consisted of records of 161,222 of daughters of 2,051 sires calving between 1995 and 2013. The reference model included fixed time-independent age at first calving and time-dependent interactions involving lactation number, region, season and age of calving, within-herd class of milk production, fat and protein content, class of annual variation in herd size and the random herd-year effect. Random sire and maternal grandsire effects were added to the model to estimate genetic parameters. The within-lactation Weibull baseline hazards were assumed to change at 0, 270, 380 days and at drying date. Within-herd milk production class had the largest contribution to the relative risk of culling. Relative culling risk increased with lower protein and fat per cent production classes and late age at first calving. Cows in large shrinking herds also had high relative risk of culling. The estimate of the sire genetic variance was 0.0472 ± 0.0017 giving a theoretical heritability estimate of 0.11 in the complete absence of censoring. Genetic trends indicated an overall decrease in functional longevity of 0.014 standard deviation from 1995 to 2007. There are opportunities for including the trait in the breeding objective for South African Holstein cattle.
利用分段韦布尔比例风险模型，对南非荷斯坦奶牛影响功能寿命的非遗传因素及其性状的遗传力进行了估计。数据包括1995年至2013年间产犊的2051头公牛的161222头女儿的记录。参考模型包括固定的首次产犊时与时间无关的年龄，以及与泌乳次数、地区、季节和产犊年龄、牛群内牛奶产量等级、脂肪和蛋白质含量、牛群规模年度变化等级相关的与时间有关的相互作用，以及随机的牛群-年份效应。将随机的父系和母系祖父效应添加到模型中以估计遗传参数。假定泌乳期内韦布尔基线风险在0、270、380天及干奶期发生变化。牛群内牛奶产量等级对淘汰相对风险的贡献最大。相对淘汰风险随着较低的蛋白质和脂肪百分比产量等级以及首次产犊年龄较晚而增加。大型萎缩牛群中的奶牛也有较高的淘汰相对风险。父系遗传方差估计值为0.0472±0.0017，在完全没有删失的情况下，理论遗传力估计值为0.11。遗传趋势表明，从1995年到2007年，功能寿命总体下降了0.014个标准差。在南非荷斯坦奶牛的育种目标中纳入该性状存在机会。
