Whole-genome DNA methylation analysis of the sperm in relation to bull fertility

Bull fertility is an important economic trait, this study identified some DNA methylation biomarkers that are associated with bull fertility.

Subfertile bulls may cause huge economic losses in dairy production since their semen could be used to inseminate thousands of cows by artificial insemination. This study adopted whole-genome enzymatic methyl sequencing and aimed to identify candidate DNA methylation markers in bovine sperm that correlate with bull fertility. Twelve bulls were selected (high bull fertility = 6; low bull fertility = 6) based on the industry's internally used Bull Fertility Index. After sequencing, a total of 450 CpG had a DNA methylation difference higher than 20% (q < 0.01) had been screened. The 16 most significant differentially methylated regions (DMRs) were identified using a 10% methylation difference cut-off (q < 5.88 × 10-16). Interestingly, most of the differentially methylated cytosines (DMCs) and DMRs were distributed on the X and Y chromosomes, demonstrating that the sex chromosomes play essential roles in bull fertility. Additionally, the functional classification showed that the beta-defensin family, zinc finger protein family, and olfactory and taste receptors could be clustered. Moreover, the enriched G protein-coupled receptors such as neurotransmitter receptors, taste receptors, olfactory receptors, and ion channels indicated that the acrosome reaction and capacitation processes are pivotal for bull fertility. In conclusion, this study identified the sperm-derived bull fertility-associated DMRs and DMCs at the whole genome level, which could complement and integrate into the existing genetic evaluation methods, increasing our decisive capacity to select good bulls and explain bull fertility better in the future.