LAUSR

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.