Sidekli, O.; Oketch, J. W.; Fair, S.; Meade, K. G.; Hollox, E. J.

{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 multiallelic 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 level of four {beta}-defensins are correlated with genomic copy number, including DEFB103. We therefore demonstrate extensive copy number variation in bovine {beta}-defensin genes, in particular DEFB103, with potential functional consequences for fertility.