Melatonin administration enhances the reproductive capacity of young rams under a southern Mediterranean environment

This study tested the effect of melatonin treatment, initiated in late February on reproductive traits of young rams. A total
of 14 young Barbarine rams were used. Seven animals were treated with three melatonin subcutaneous implants
(Melatonin) on 28 February while the remaining rams remained untreated (Control). After 60 days of melatonin administration,
scrotal circumference reached average values of 32.1 ± 1.54 and 29.5 ± 1.0 cm for Melatonin and Control
animals, respectively (P < 0.05). Semen characteristics did not differ between groups; melatonin treatment tended
(P = 0.091) to increase sperm concentration 60 days after implantation when means reached 5.87 ± 0.703 and
4.61 ± 0.654 × 109 spermatozoa/mL for Melatonin and Control rams, respectively. Melatonin treatment significantly
affected total activity time, number of lateral approaches and mount attempts in comparison to controls. During a 6-h
sampling period, mean plasma testosterone concentrations increased as a result of melatonin treatment (P < 0.001) and
testosterone pulse frequency averaged 3.45 ± 2.24 and 1.25 ± 1.0 (P = 0.086) for Melatonin and Control rams. Data
clearly suggest that abrupt treatment of young rams with melatonin implants in winter is sufficient to improve reproductive
traits.