Sperm DNA 5-mC and RNA m 6A methylation are differently affected during periods of body weight losses and body weight gain of young and mature breeding bulls.

Abstract Aiming to characterize the effects of nutritional status on epigenetic markers, such as DNA 5-mC methylation and RNA m 6A methylation, of bovine sperm, twelve Angus × Hereford crossbred breeding bulls were submitted to nutritional changes for a period of 180 days: no change in BW (Phase 1 = 12 d); BW loss (Phase 2 = 78 d); and BW gain (Phase 3 = 90 d) in a repeated measures design. Animals were fed Beardless wheat (Triticum aestivum) hay and mineral mix. Statistical analyses were performed using SAS 9.4 (SAS Inst., Cary, NC). Higher levels of RNA m 6A (P = 0.004) and DNA methylation (P = 0.007) of spermatic cells were observed at Phase 2 compared with Phase 1. In Phase 3, sperm RNA m 6A methylation levels continued to be higher (P = 0.004), whereas the DNA of sperm cells was similar (P = 0.426) compared with the Phase 1. Growing bulls had a tendency (P = 0.109) of higher RNA m 6A methylation levels than mature bulls. Phase 2 altered scrotal circumference (P < 0.001), sperm volume (P = 0.007), sperm total motility (P = 0.004), sperm progressive motility (P = 0.004), total sperm count (P = 0.049), normal sperm (P < 0.001), abnormal sperm (P < 0.001), primary sperm defects (P = 0.039), and secondary sperm defects (P < 0.001). In Phase 3, bulls had scrotal circumference, sperm volume, sperm motility, sperm progressive motility, total sperm count, normal and abnormal spermatozoa, and primary and secondary spermatozoa defects similar to Phase 1 (P > 0.05). Serum concentrations of insulin-like growth factor-1 (IGF-1) and leptin decreased during Phase 2 (P = 0.010) while no differences (P > 0.05) were detected between Phase 3 and 1; growing bulls tended (P = 0.102) to present higher leptin levels than mature bulls. Specific for mature bulls, DNA methylation was positively correlated with leptin concentration (0.569, P = 0.021). Whereas for young bulls, DNA methylation was positively correlated with abnormal spermatozoa (0.824, P = 0.006), primary spermatozoa defect (0.711, P = 0.032), secondary spermatozoa defect (0.661, P = 0.052), and negatively correlated with normal spermatozoa (−0.824, P = 0.006), total sperm count (−0.702, P = 0.035), and sperm concentration (−0.846, P = 0.004). There was no significant correlation (P > 0.05) between RNA m 6A and hormones and semen traits. In conclusion, the nutritional status of breeding bulls alters epigenetic markers, such as DNA methylation and RNA m 6A methylation, in sperm, and the impact of change seems to be age-dependent. These markers may serve as biomarkers of sperm quality and fertility of bulls in the future. Detrimental effects on sperm production and seminal quality are observed at periods and places when and where environmental and nutritional limitations are a year-round reality and may carry hidden players that may influence a lifetime of underperformance.