Prolonged Sexual Rest on Fresh Semen Quality Across Different Age Groups in Holstein Friesian Bulls

Sexual rest and age of bulls affect semen quality. This study aimed to evaluate fresh semen quality prior to and following a long period of sexual rest in six Holstein Friesian bulls at the Lembang Artificial Insemination (AI) Center. The bulls were categorized into age groups of 3, 5, and 9 years. Secondary data from 2024–2025 on the semen volume, pH, sperm concentration, total sperm count (TSC), and sperm motility were analyzed. Bull libido, sperm viability, and abnormality were also evaluated on the first semen collection following sexual rest. The results indicated that bulls generally exhibited relatively good libido following sexual rest. Nevertheless, prolonged sexual rest decreased semen volume, sperm concentration, TSC, and sperm motility, with TSC and motility also significantly influenced by age. Sperm abnormality was elevated in the first collection following sexual rest. Notably, older bulls (9 years) exhibited a more marked decline in sperm motility, indicating a significant age effect. This was likely due to their reduced ability to maintain an optimal epididymal microenvironment as a consequence of prolonged sexual rest. In conclusion, regular semen collection intervals are crucial for maintaining optimal semen quantity and quality, which maximizes the efficiency of semen production.