This study investigated the effect of age and season on sperm morphology in 271 Friesland bulls at an artificial insemination center over 5 years. The results showed:
1) Bulls aged 36-48 months had the best sperm morphology, with over 70% normal sperm and lowest major defects.
2) Season affected sperm morphology, with the highest normal sperm in spring (84.4%) and lowest in summer (72.8%).
3) Both age and season significantly impacted the percentage of normal sperm and major defects like pyriforms. Younger bulls had more defects in winter while older bulls were worse in summer.