Relationship between sperm nuclear DNA fragmentation index and hormonal status in breeding bulls

Relevance. The efficiency of cattle breeding is directly dependent on reproduction quality, where the condition of spermatozoa in breeding bulls plays a crucial role. One of the critical factors is DNA fragmentation in spermatozoa, which can cause genetic abnormalities and reduce the effectiveness of artificial insemination. Hormonal imbalance, particularly testosterone and estradiol levels, may affect DNA integrity. This study aims to investigate the influence of bulls’ hormonal status on DNA fragmentation in their spermatozoa. Methods. The study was conducted on 43 Holstein bulls. DNA fragmentation was assessed using the alkaline comet assay, with a minimum of 250 spermatozoa analyzed per sample. Hormonal status (testosterone, estradiol, thyroxine) was evaluated through enzyme-linked immunosorbent assay (ELISA) of blood serum. Statistical analysis was performed using SPSS v.23 software, employing variance analysis and Student’s t-test. Results. Over 98% of spermatozoa exhibited intact DNA, while moderate and severe damage was observed in 1% and 0.8% of cells, respectively. Bulls with intact DNA showed 62.3% and 72% higher testosterone levels compared to those with DNA damage (p < 0.05). Conversely, estradiol concentration was 40% higher in bulls with fragmented DNA. Correlation analysis revealed a weak but significant negative association between testosterone and DNA fragmentation (ρ ≈ -0.20) and a positive association between estradiol and DNA damage (ρ ≈ 0.18). Thyroxine levels showed no significant differences between groups. Conclusions. High testosterone levels are associated with reduced DNA fragmentation, while elevated estradiol may contribute to its increase, potentially due to oxidative stress. These findings highlight the importance of hormonal balance in maintaining sperm DNA integrity in breeding bulls.