High-throughput nuclear morphometric analysis for pig sperm quality assessment

Artificial insemination (AI) is commonplace in commercial pig breeding, and as such, ensuring sperm sample quality is of utmost importance to avoid reduced farrowing rates and litter sizes. Here, we have used high-throughput nuclear morphometric analysis to compare pig sperm samples categorised as meeting the AI standard (AIS) or not meeting the AI standard (N-AIS) (50 vs. 44 samples from unique boars, respectively). We show that pig sperm nuclei are asymmetric, that samples contain phenotypic shape abnormalities that show continuous variation and that samples classed as N-AIS have more abnormally shaped sperm than AIS samples. This variation is not detected in conventional analysis. The specific phenotypes identified suggest the disruption of key aspects of spermiogenesis and indicate future avenues for improving pig sperm quality. Additionally, we find that the distribution and severity of abnormal sperm phenotypes were significantly associated with the day of semen collection, indicating that environmental factors may influence sperm morphology. High-throughput nuclear morphometric analysis therefore reveals significant differences in sperm head morphology between AIS and N-AIS pig sperm samples and has the potential to be further developed as a tool for sperm assessment both in the pig breeding industry and in other species.