Sperm morphology differences associated with pig fertility

Artificial insemination is routinely used in commercial pig breeding, for which the use of high quality semen samples is imperative. Currently, semen quality is determined manually by morphological assessment. This method leads to high inter-operator variability due to its subjective nature. The development of a semi-automated software-based approach to assess sperm morphology would enable faster identification of morphological defects and permit identification of subtle differences that may affect fertilisation success. Here we have used a novel method to comprehensively analyse pig sperm nuclear morphology in greater detail than was previously possible. Semen samples from 50 fertile and 50 sub-fertile samples that had been previously manually categorised as fertile or sub-fertile were analysed using this new method, with at least 200 fixed and DAPI (49,6-diamidino-2-phenylindole) stained sperm heads imaged per sample. Differences in sperm nuclear morphology were observed between fertile and sub-fertile samples; specifically, fertile samples were associated with higher mean nuclear area, a consequence of a greater head width and a lower variability between sperm heads. This novel, unbiased and fast analysis method demonstrates a significant difference in sperm head morphology between fertile and sub-fertile animals, and has the potential to be further developed and used as a tool for sperm morphology assessment in the pig breeding industry.