The Percentage of Normal Sperm Declines in Consecutively Collected Ejaculates of Ram Semen

Sperm morphology is an important marker of fertility in livestock. Since poor sperm morphology can disqualify a sire from being sold or used for breeding, it is crucial to understand the factors that influence changes in sperm morphology over time. It is often hypothesised that little variation exists in sperm morphology from ejaculate to ejaculate so long as factors such as nutrition, season, health, and thermal status remain the same. This study aimed to test this hypothesis by investigating the morphology of sperm collected from rams (Ovine aries) (n = 3) twice daily, three times per week, over an 8-week period. Sperm morphology was evaluated using an eight-category classification system. Results revealed that each ram exhibited high levels of variability, with only 10.4% of ejaculates within ±5% of their own mean percentage normal sperm (PNS). The percentage of normal sperm over the 8-week period was significantly influenced by intra-week variation, although no consistent trend was observed across the full duration of the study. Within each day, a significant decline in the percentage of normal sperm was observed when a second ejaculate was collected consecutively. This decline was primarily attributed to an increase in cytoplasmic droplets and midpiece abnormalities. These findings suggest that rams subjected to regular semen collection in a controlled environment are likely to exhibit considerable variation in the percentage of normal sperm from ejaculate to ejaculate. For artificial breeding centres and veterinarians, repeated semen collection on the same day may reduce the proportion of normal sperm. As such, assessment of each separate ejaculate for sperm morphology is recommended before pooling for processing or insemination.