Cattle breeding routinely uses crossbreeding between subspecies (Bos taurus taurus and Bos taurus indicus) to form composite breeds, such as Brangus. These composite breeds provide an opportunity to identify recent selection signatures formed in the new population and evaluate the genomic composition of these regions of the genome. Using high-density genotyping, we first identified runs of homozygosity (ROH) and calculated genomic inbreeding. Then, we evaluated the genomic composition of the regions identified as selected (selective sweeps) using a chromosome painting approach. The genomic inbreeding increased at approximately 1% per generation after composite breed formation, showing the need of inbreeding control even in composite breeds. Three selected regions in Brangus were also identified as Angus selection signatures. Two regions (chromosomes 14 and 21) were identified as signatures of selection in Brangus and both founder breeds. Five of the 10 homozygous regions in Brangus were predominantly Angus in origin (probability >80%), and the other five regions had a mixed origin but always with Brahman contributing less than 50%. Therefore, genetic events, such as drift, selection, and complementarity, are likely shaping the genetic composition of founder breeds in specific genomic regions. Such findings highlight a variety of opportunities to better control the selection process and explore heterosis and complementarity at the genomic level in composite breeds.

牛育种通常使用亚种之间的杂交（金牛座牛和印度牛）形成复合品种，例如白兰格斯（Brangus）。这些复合品种提供了识别新种群中最近形成的选择特征并评估基因组这些区域的基因组组成的机会。使用高密度基因分型，我们首先鉴定了纯合性（ROH）并计算了基因组近交。然后，我们使用染色体绘制方法评估了确定为选定（选择性扫描）的区域的基因组组成。复合品种形成后，基因组近交每代增加约1%，表明即使在复合品种中也需要近交控制。布朗格斯的三个选定区域也被确定为安格斯选择特征。两个区域（14 号和 21 号染色体）被确定为 Brangus 和两个创始品种的选择特征。布兰格斯的 10 个纯合区域中，有 5 个区域主要是安格斯起源（概率 >80%），其他 5 个区域具有混合起源，但婆罗门的贡献始终低于 50%。因此，漂移、选择和互补等遗传事件可能会影响特定基因组区域中创始品种的遗传组成。这些发现强调了更好地控制选择过程并探索复合品种基因组水平上的杂种优势和互补性的各种机会。