Supplementing a skimmed milk–egg yolk-based extender with L-carnitine helps maintain the motility, membrane integrity and fertilizing capacity of chilled ram sperm

This study examines the effect of L-carnitine (LC) on chilled ram semen stored for up to 96 hr. Semen samples were collected, placed in a skimmed milk + 6% egg yolk extender, pooled, aliquoted and diluted with the same extender supplemented with different LC concentration: 0 (control), 1 mM (LC1), 2.5 mM (LC2.5), 5 mM (LC5), 7.5 mM (LC7.5) or10 mM (LC10). Sperm kinetics and membranes (plasma, acrosome and mitochondrial) were examined using the CASA system and triple fluorescence staining (PI/ PNA-FITC/Mitotracker). The progressive motility was greater (p <.05) with LC7.5 treatment than the control sperm at 96 hr. The curvilinear velocity (p <.01) and the percentage of sperm with intact membranes (plasma/acrosome/mitochondria) (p <.01) were greater with all LC treatments than the control group at all times. Straight line velocity was greater (p <.01) with LC5 and LC7.5 treatments than the control group after 48 hr. The LC5 group also returned lower ALH values (p <.05) than these seen for the control groups after 48 hr. The fertilizing capacity of LC5 samples stored at 15°C for 2 hr (LC5-15°C-2h) and at 5°C for 24 hr (LC5-5°C-24h) was tested in three ewe groups via cervical fixed-time artificial insemination. In two groups, the fertilizing capacity of the LC5-5°C-24h was reduced (p <.001). In the remaining group, however, no significant difference was seen between the LC5-15°C-2h and LC5-5°C-24h sperm in this respect (pregnancy rates 52.4% versus 42.8%; p >.05). Overall, the present results suggest that supplementing skimmed milk–egg yolk-based extenders with LC has a positive effect on chilled sperm variables and fertilizing capacity.