摘要
Composite crosses result from the mating of two or more distinct cattle breeds. Breeding performance may improve rapidly using a well-organized composite breeding system and a clear selection index. The KiwiCross® is a popular composite cross in New Zealand, combining Holstein-Friesian (high milk production) and Jersey (high milk fat). Production efficiency (PR), a key selection index, is calculated by dividing milk solids produced by mature live weight. Over decades of genetic improvement, KiwiCross® increased milk production significantly. We hypothesized that certain genomic regions from Holstein-Friesian or Jersey breeds were preserved due to artificial selection based on PR. Analysis of genomic regions using XP-EHH, hapFLK, and ROH haplotype statistics revealed selection signatures on BTA 7 and 20 in both high- and low-performance animals, with distinct regions linked to Holstein-Friesian and Jersey ancestry. Our findings suggest that selection acted on different genomic regions across generations and that preserving key ancestry-specific haplotypes is crucial for maintaining performance in composite breeds. Breeders must recognize that selection for specific traits can alter allele frequencies and lead to the loss of beneficial breed-specific haplotypes over time.
摘要译文
复合杂交是由两个或多个不同的牛品种的交配引起的。使用良好的复合繁殖系统和清晰的选择指数可以迅速改善育种性能。Kiwicross®是新西兰的流行复合十字架，结合了Holstein-Fiesian（高牛奶生产）和泽西岛（高牛奶脂肪）。生产效率（PR）是一个关键选择指数，是通过分配成熟活重的牛奶固体来计算的。在数十年的遗传改善中，Kiwicross®大大增加了牛奶的产量。我们假设来自荷斯坦 - 弗里斯或泽西岛品种的某些基因组区域由于基于PR的人工选择而保留了。使用XP-EHH，HAPFLK和ROH单倍型统计数据对基因组区域进行分析表明，在高性能和低性能动物中，BTA 7和20的选择特征具有与Holstein-Fiesian和Jersey Ancestry相关的不同区域。我们的发现表明，选择对几代人的不同基因组区域作用，并且保留主要祖先特异性单倍型对于维持复合品种的性能至关重要。育种者必须认识到，对特定性状的选择可以改变等位基因频率，并导致随着时间的流逝而导致有益品种特异性单倍型的丧失。
Mohd Jaafar; Bevin Harris; Heather J. Huson. The Effect of Continuous Selection in KiwiCross® Composite Breed on Breed Ancestry and Productivity Performance[J]. Animals, 2025,15(2): 175