Post mortem time and season alter subpopulation characteristics of Iberian red deer epididymal sperm

We have studied the effect of post mortem time and season on sperm subpopulation pattern and characteristics. We used epididymal samples from free-ranging Iberian red deers harvested during the hunting season. We studied samples at different moments of the year (rut, transition period and post-rut), and at different times post mortem (up to 4 days). Sperm were extracted from the cauda epididymis and their motility was evaluated by means of a CASA system. A principal component and clustering analysis were carried out to identify subpopulations. Post mortem time caused a significant decrease in motility quality, and a general deterioration in subpopulation characteristics. We found three subpopulations the first day, and the one indicating good sperm quality decreased with post mortem time until it disappeared on the fourth day. This may indicate considerable impairment of the samples after 72 h post mortem, which could compromise their use in AI programs. With regard to season, subpopulation pattern and characteristics were better in the transition and post-rut periods. Moreover, we found one subpopulation formed by mature spermatozoa, which increased from rut to post-rut. This might be a negative fact, because samples collected after the rut may undergo hypermaturation, which possibly impairs fertility. Our results are of interest for the management of wildlife germplasm banks based on post mortem sperm recovery.