l-cysteine prolonged fresh boar semen qualities, but not for docosahexaenoic acid

The present study aimed to develop a long-term fresh boar semen extender by adding l-cysteine and docosahexaenoic acid (DHA) into Beltsville thawing solution (BTS)-based extender. Semen samples were collected from six boars, diluted at a concentration of 3 × 10⁹ spermatozoa/100 ml and allocated into 10 groups as follows: BTS, Merck III^®, Androstar^® Plus, Modena^TM, DHA 1.5 mg/ml, 3 mg/ml and 6.25 mg/ml, l-cysteine 2.5 mM, 5.0 mM and 10 mM. All extended semen samples were stored at 18 °C, and were evaluated for progressive motility, viability, acrosome integrity, pH and osmolality on days 0, 1, 3, 5 and 7 of storage. The results documented that on day 3, l-cysteine at 2.5 mM showed the significantly highest percentage (78.8%) of progressive motility, but not different from Modena^TM (78.8%) and Androstar^® Plus (71.3%) (P < 0.05). On day 5, l-cysteine at 2.5 mM maintained progressive motility and viability up to 73.8% and 77.9%, respectively, but not different from Modena^TM (78.8% and 74.8%) and Androstar^® Plus (70.0% and 76.8%) (P < 0.05). On day 7, superior progressive motility (71.3%, 77.5% and 72.5%) and viability (72.8%, 77.3% and 69.8%) were found for l-cysteine at 2.5 mM, Modena^TM and Androstar^® Plus groups, respectively, when compared to the other groups (P < 0.01). However, in the present study, DHA supplementation failed to maintain fresh boar semen qualities during storage. In conclusion, adding l-cysteine at a concentration of 2.5 mM in BTS-based extender is the optimal concentration for the preservation of fresh boar semen at 18 °C for seven days.