Liquid preservation of boar semen: Insights into the sperm’s energy budget

As many fertilization-relevant sperm functions rely on the availability of ATP, semen preservation should maintain a well-balanced energy budget. Our aim was to shed light on the spermatozoa’s energy balance during long-term storage at 17°C, which is the conventional storage temperature of boar semen, and under hypothermic condition at 5°C, as recently introduced into swine insemination for prevention of microbial growth. First, improved ATP and adenylate energy charge (EC) assay protocols were validated for the use in spermatozoa. The assays were then applied to semen samples (n=7 boars) stored at 17°C in Beltsville Thawing Solution for up to seven days. Basic ATP levels and EC values remained stable throughout storage (p>0.05). However, re-establishing of sperm motility upon rewarming to 38°C revealed an increased (p<0.05) net investment of ATP with ongoing storage time, reaching 25% of the preserved ATP level (452±57 pmol/105 sperm) after five days.