Intra- and inter-stallion variation in sperm morphology and their relationship with fertility.

This research explores the variation in sperm morphology within and between Thoroughbred stallions, and how these variations affect fertility. It reveals substantial differences in sperm morphology both within individual stallions and between different stallions. However, these variations do not affect the day-to-day fertility of individual stallions or the pregnancy rate of the mares they mate with. The study also identifies certain sperm features affecting pregnancy success and could be used to predict fertility disparities among stallions.

Examination of Intra-stallion Variation in Sperm Morphology

• The study first addresses intra-stallion variation, referring to variations observed within individual stallions’ sperm morphology.
• Researchers found a significant degree of intra-stallion variation during the breeding season with a coefficient of variation at 20%.
• Despite these variations, these morphological differences had no observable impact on the fertility of same-day sperm samples from the same stallion, illustrating that sperm morphology does not directly influence a stallion’s fertility on a day-to-day basis.

Exploration of Inter-stallion Variation in Sperm Morphology and Fertility

• The researchers then discuss inter-stallion variation, referring to the differences in sperm morphology among different stallions.
• A larger degree of variation was found in inter-stallion comparisons with a coefficient of variation at 38%.
• The sperm morphologies that significantly predicted fertility included the percentage of normal spermatozoa, abnormal or detached heads, general mid-piece abnormalities, coiled tails, and premature germ cells.
• Despite the larger variation in morphology, the mare pregnancy rates were not affected, suggesting that while sperm morphology may differ significantly between stallions, general fertility rates remain steady.

Implications for Fertility and Breeding

• Certain morphological features of stallion spermatozoa were identified as influencers of successful pregnancy establishment. These include the percentage of normal spermatozoa, abnormal or detached heads, mid-piece abnormalities, coiled tails, and premature germ cells.
• This information is useful because it can be used as predictive markers for understanding differences in fertility among stallions, potentially enhancing breeding success and efficiency in the equine domain.