Effects of different L-carnitine concentrations on post-thaw ram semen characteristics and fertilizing potential

The main goal of the present study was to evaluate the effects of different L-carnitine concentrations on post-thaw ram semen characteristics and fertilizing potential. Five sexually mature Zandi rams (3–4 years of age), with confirmed fertility, were used in the six replicates of this experiment in the breeding season. Semen samples (n = 30, 6 samples per ram) were collected using an artificial vagina twice a week. Following the collection and initial assessment of ejaculates, all semen samples were pooled to eliminate individual variations. Plant-based freezing extender containing soybean lecithin was supplemented with varying concentrations of L-carnitine (0, 1, 2, 5, and 10 mM), and semen was diluted to a final concentration of 100 × 10⁶ spermatozoa/0.25-mL straw before freezing in liquid nitrogen. Sperm motility, viability, mitochondrial function, acrosome integrity, apoptosis, DNA fragmentation, reactive oxygen species accumulation, and fertilizing potential in vivo were assessed. Ram semen cryopreserved in a freezing extender supplemented with 5 mM of L-carnitine exhibited the highest (P ≤ 0.05) average path velocity and percentages of sperm with total/progressive motility, as well as the highest (P ≤ 0.05) proportion of sperm with intact mitochondria, plasma membranes, and acrosomes. This dose of L-carnitine was also associated with the lowest (P ≤ 0.05) levels of apoptosis, DNA fragmentation, reactive oxygen species accumulation, and lipid peroxidation as well as with the highest (P ≤ 0.05) pregnancy and lambing rates in artificially inseminated ewes. Therefore, supplementing the semen extender with 5 mM of L-carnitine is an effective method for preserving the quality and fertilizing potential of frozen-thawed ram semen.