To verify the efficiency of regression model taking breed composition and heterozygosity as covariate in crossbred dairy cattle population, and provide theoretical solutions for efficient crossbreeding system and proper genetic evaluation methodology in practice,according to the situation of Chinese dairy industry, a scenario was simulated in the current study which low performance Holstein cow crossbred with high ranking Monbeliarde and Fleckvieh bulls. Random mating or three-breed rotational crossbreeding was simulated for 17 years with generation overlapped.The results showed that the average heterozygosity stabilized from the 7th year onwards under both mating patterns, and the three-breed rotation showed higher overall average heterozygosity than random mating. The milk and growth performance of low production Holstein herd had been improved after crossbreeding for 17 years and the rotational mating patterns made better improvement. Moreover,by fitting regression on breed composition and heterozygosity, both single-trait and multiple-trait animal model could be used for genetic evaluation in multi-breed population efficiently,and the differences between them could be negligible. For low production Holstein herd,crossbreeding with elite double purpose breed could be an effiaent mean to improve both milk and growth performance,regression model is suitable for genetic evaluation in multi-breed population.%为验证在奶牛杂交群体中将品种组成和杂合度作为协变量的遗传评估理论,为奶牛杂交模式选择和杂交群体遗传评估等实际问题提供理论依据,结合我国奶业现状,本研究模拟了在低产荷斯坦牛群引入法系蒙贝利亚牛、德系西门塔尔牛进行杂交,采用随机交配和三品种轮回杂交模式、群体世代重叠17年的繁育过程.群体杂合度在第7年后趋于平衡,轮回杂交模式的群体杂合度高于随机交配.经过杂交,原中低产荷斯坦牛群体在产奶性能、生长性能方面都有进展,轮回杂交提高幅度相对略高.此外,利用品种效应和杂合度效应剖分杂种优势,采用单性状和多性状动物模型对模拟群体进行遗传评估,效果基本一致,都可以很好地用于杂交群体的遗传评估.结果表明,对荷斯坦牛中低产群体进行杂交,可实现生产性能和效益的提高,回归模型可用于多元群体的遗传评估.
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