β-Defensin gene copy number variation in cattle

beta-Defensins are peptides with antimicrobial roles, characterized by a conserved tertiary structure. Beyond antimicrobial functions, they exhibit diverse roles in both the immune response and fertility, including involvement in sperm maturation and function. Copy number variation (CNV) of beta-defensin genes is extensive across mammals, including cattle, with possible implications for reproductive traits and disease resistance. In this study, we comprehensively catalogue 55 beta-defensin genes in cattle. By constructing a phylogenetic tree to identify human orthologues and lineage-specific expansions, we identify 1 : 1 human orthologues for 35 bovine beta-defensins. We also discover extensive beta-defensin gene CNV across breeds, with DEFB103, in particular, showing extensive multi-allelic CNV. By comparing beta-defensin expression levels in testis from calves and adult bulls, we find that 14 beta-defensins, including DEFB103, increase in expression during sexual maturation. Analysis of beta-defensin gene expression levels in the caput of adult bull epididymis, and beta-defensin gene copy number, in 94 matched samples shows expression levels of four beta-defensins are correlated with genomic copy numbers, including DEFB103. We therefore demonstrate extensive CNV in bovine beta-defensin genes, in particular DEFB103, with potential functional consequences for fertility.