L-Carnitine enhances porcine sperm quality, longevity, and zona pellucida binding in cooled semen

Porcine breeding industries typically ensure the viability of boar artificial insemination doses during a 5-day liquid storage period at 17 °C. This study aimed to investigate whether the addition of L-carnitine (LC) to boar semen doses on different days of cooled storage could extend their usability. In experiment 1, LC was added to porcine semen doses on the fifth day (d5) of cooled storage performing five treatments control (no LC), 0.5, 1-, 5- and 10-mM LC. On d6 and d8 of storage, semen samples were evaluated for sperm motility and kinematic parameters, membrane functionality, and hydrogen peroxide and nitrite concentrations. In experiment 2, the number of sperm bound to the zona pellucida (ZP) was determined, as a way to investigate sperm penetration capability from boar insemination doses, with co-incubation with porcine oocytes. LC concentration that produced the most favorable outcomes in Experiment 1 was chosen to experiments 2 and 3, performing two treatments in the absence and with the LC. In Experiment 3, LC was added to cooled porcine semen doses after one day of storage (d1), and the same evaluations of experiment 1 were conducted on days 5, 7, 9, and 12, including sperm membrane integrity. The addition of 10 mM LC on d5 and d1 of storage improved sperm motility, which was extended up to 8 and 12 days of cooled storage, respectively. LC addition on d5 of storage increased sperm membrane functionality, while when added to semen on d1 of storage, it decreased NO₂ ^- concentration on d9. On d6 of cooled storage 10 mM LC increased the number of sperm bound to ZP compared to the control. In conclusion, adding 10 mM LC to porcine semen doses at 17 °C improved sperm characteristics and ZP binding, ultimately enhancing sperm viability for up to 12d.