33 Effect of exogenous melatonin administration on testicular biometry, libido parameters, seminal parameters, hormone levels, and freezability of Sirohi buck semen during the non-breeding season in Southern Rajasthan

Abstract

The aim of this work was to determine the effect of administration of exogenous melatonin on the testicular biometry, libido parameters, hormone levels, and freezability of semen during the non-breeding seasons in adult Sirohi bucks. Experiments of 4 and 8 weeks were carried out during non-breeding seasons at different times. Twelve bucks, 2 to 3 years of age, were split into melatonin-treated and control groups, with 6 bucks in each group. Throughout the 2 experimental periods, all bucks were permanently kept outdoors under conditions of natural daylength and at ambient temperature. Bucks in the treated group were subjected to single subcutaneous injection of a powder form of melatonin mixed with corn oil at the dose rate 18 mg per 50 kg on the first day of experiment; bucks in the control group received sterile corn oil injected subcutaneously in control group. Ejaculates were taken from the bucks by artificial vagina (AV) once per week and their reaction time (the elapsed time between exposure to stimuli and first ejaculation) was recorded. Testicular biometry, serum testosterone, and serum melatonin were determined weekly before semen collection. Ejaculates were cryopreserved and thawed weekly and the same quantitative and qualitative variables were measured as for fresh semen samples. Melatonin significantly (P < 0.05) improved testicular biometry, libido parameters, and hormone levels compared with the control group during weeks 3 and 4 of the first experiment and from week 5 onward of the second experiment (P < 0.05). Semen volume (mL) improved to 0.70 ± 0.039 vs. 0.48 ± 0.009 and 0.94 ± 0.036 vs. 0.56 ± 0.032 in first and second experiments. Greater (P < 0.05) progressive motility (%) was noted in the melatonin group (84.59 ± 1.472 and 86.88 ± 0.797) during experiments 1 and 2. Semen quality of each straw from each ejaculate was evaluated after proper thawing within 24 h. Mean post-thaw live sperm percentage for experiments 1 and 2 was 69.25 ± 0.382 and 66.90 ± 0.779, progressive motility was 50.42 ± 0.948 and 58.75 ± 1.058, and curled tail sperm count were 51.00 ± 0.715 and 61.36 ± 0.773, respectively. In conclusion, the results of present experiments are novel regarding the use of single subcutaneous melatonin injection during the non-breeding season to improve variables associated with the fertility potential of the Sirohi buck and frozen-thawed seminal parameters.