L-carnitine added to post-thawed semen acts as an antioxidant and a stimulator of equine sperm metabolism.

The objective of this study was to enhance the in vitro sperm quality and in vivo fertility of frozen-thawed equine semen by the addition of l-carnitine (LC) to post-thawed semen. Different concentrations of LC were added to thawed samples to obtain four treatments control and 0.5, 1 and 2 mM LC. In the in vitro experiments, sperm motility and kinematics, membrane integrity and intracellular calcium ion concentration ([Ca2+ ]i ) were investigated, and the antioxidant bioactivity of LC was assessed by measuring hydrogen peroxide and nitrite concentrations (NO2 - ). The fertility rate was assessed via the artificial insemination of mares. The treatment with 1 mM LC increased sperm [Ca2+ ]i (60.6 ± 0.05 AU), reduced nitrite concentration (39.1 ± 14.9 µM/µg protein), increased the sperm straightness percentage (STR: 78.3 ± 5.3%) and increased the pregnancy rate (75%) as compared to the control ([Ca2+ ]i 48.4 ± 0.05 AU, NO2 - concentration 63.1 ± 14.4 µM/µg protein, STR 67.5 ± 7.9%, 12.5% pregnancy rate, p < 0.05). These results suggest that 1 mM LC acts as an antioxidant and stimulator of sperm metabolism in post-thawed equine semen, increasing the fertility rate. Thus, addition of LC might be an alternative to improve the fertility of poor quality post-thawed equine semen.

Does Coenzyme Q10 Exert Antioxidant Effect on Frozen Equine Sperm?

During semen cryopreservation, the sensitivity of equine sperm to oxidative stress is increased by the eliminated seminal plasma. Thus, antioxidant addition to the semen extender can be helpful to the sperm survival after freezing and thawing. This work aimed to test whether coenzyme Q10 (CoQ10) added in different concentrations to the INRA 82 freezing extender has antioxidant function on equine sperm to improve its fertilizing ability. Semen samples from five stallions were frozen with the extenders: (T1) INRA 82, control, (T2) T1+ 5 µM CoQ10, (T3) T1+ 25 µM CoQ10, and (T4) T1+ 50 µM CoQ10. After sample thawing, sperm motility and kinetics characteristics were evaluated using a computer-assisted sperm analysis and sperm membrane functionality and integrity were evaluated with a hypo-osmotic swelling test and an epifluorescence microscopy, respectively. The nitrite (NO2-) and hydrogen peroxide (H2O2) concentrations of the semen samples were measured with spectrophotometry. There was no difference on the sperm characteristics among all treatments (P > .05). However, the 25 µM CoQ10 (T3) decreased NO2- concentration (6.7 ± 2.2 µM/µg protein) compared with the treatments T1, T2, and T4 (64.3 ± 3.7, 59.4 ± 5.3, 45.1 ± 8.6 µM/µg protein), respectively, as well H2O2 concentration (1.8 ± 0.3 µM/µg protein) compared with the control (4.6 ± 0.4 µM/µg protein) and 5 µM CoQ10 treatments (4.8 ± 0.2 µM/µg protein, P < .05). In conclusion, 25 µM CoQ10 plays a significant role as antioxidant to the frozen equine sperm, decreasing NO2- and H2O2 concentrations. Thus, its addition to the INRA 82 freezing extender may be beneficial to the fertilizing ability of equine semen.