Effect of melatonin treatment on semen parameters and endocrine function in Black Racka rams out of the breeding season

The influence of melatonin implantation on scrotal circumference, semen quantitative and qualitative parameters, plasma melatonin as well as basal and provoked testosterone concentration was evaluated in Black Racka rams in the non-breeding season. Twelve rams were used in the 60-day-long trial; six of them were implanted (M) with Melovine® (Ceva, Libourne, France) subcutaneously on day 0 (10th May) and 30 days later again, while the other six rams remained untreated (C). Scrotal circumference (SC) was measured and semen was collected weekly and assorted to two 30-day-long periods. Blood samples were collected on days 0, 30 and 60 and basal testosterone level and GnRH-induced testosterone response were evaluated. Ejaculate volume (VOL) increased in both groups from the minimum value at the beginning of the trial (0.52 ± 0.08 ml vs. 0.44 ± 0.06 ml) to the maximum at 60 days after the first implantation (0.82 ± 0.07 ml vs. 0.73 ± 0.05 ml, P < 0.05). Significant differences were found in SC, VOL and total spermatozoa number from day 30 to day 60 after the first melatonin implantation between the treatment groups (P < 0.05). The statistical analyses revealed no difference between treated and control groups regarding total motility % (TM%) and progressive motility % (PM%) at the first implantation and the last sampling. However, at the second implantation melatonin treatment had a positive effect on TM% (P < 0.05) and PM% (P < 0.001) compared to group C. Basal testosterone (Tb) concentrations were not different between groups at the beginning of the treatment; nevertheless, 60 days later a significantly elevated Tb level was measured in group M compared to C (P < 0.05). Testosterone response after the GnRH test was not different between groups at the first and second implantation, while at the third sampling elevated Tb was detected and the provoked testosterone concentrations (Tincr) were also higher in group M at 30 and 60 min after GnRH treatment (P < 0.05). Plasma melatonin level was increased by implantation to 445.3 ± 91.55 pmol/L measured at day 30 compared to 92.4 ± 9.15 pmol/L on day 0 (P < 0.05), and a further increase of melatonin concentration was recorded after the insertion of the second implants at day 60 (699.45 ± 163.91 pmol/L; P < 0.05). In conclusion, melatonin implantation in the non-breeding season (at the beginning of May) significantly improved the endocrine and exocrine function of testicles and some quantitative as well as quality parameters of the ejaculate in rams of the Hungarian native breed Black Racka.