Effect of Estrus Synchronization/induction in Ouled Djellal ewes using combinations of melatonin, GnRH, and Prostaglandin F

The present study evaluated the efficacy of melatonin implants alone or in combination with hormonal treatments for inducing ovarian activity and improving reproductive performance during seasonal anoestrus in Ouled Djellal ewes in Algeria. Sixty multiparous, non-lactating ewes were randomly assigned to four groups: melatonin alone (MEL), melatonin plus Ovsynch (MEL + GPG), melatonin plus progesterone (MEL+P4), and untreated controls. Estrus detection was performed for 40 days after treatment, and reproductive performance was assessed through estrus onset, pregnancy and fertility rates, litter size, productivity, and plasma P4 concentrations (ng/mL). The MEL+P4 protocol was the most effective in inducing early estrus and improving fertility outcomes. Within the first 72 h, 67% of ewes in this group exhibited estrus, compared with 10% in the MEL group and no estrous response in the MEL + GPG or control groups (P < 0.05). By 40 days, the cumulative estrus response was high across groups (82–100%), with no significant differences among treatments. However, the onset of estrus occurred significantly earlier in MEL+P4 (108 h) than in the MEL, MEL + GPG, and control groups, in which estrus onset exceeded 280 h (P < 0.05). At 72 h, both pregnancy and fertility rates were highest in MEL+P4 (67% and 87.5%, respectively; P < 0.001), whereas other groups showed minimal responses. At 40 days, fertility exceeded 90% in MEL+P4 and MEL, compared with only 45.5% in controls (P < 0.05). MEL+ P4 also achieved the greatest litter size (1.77 ± 0.26 lambs/ewe) p < 0.05 and productivity (1.38 ± 0.20 lambs/ewe) with productivity significantly higher only vs. control. Progesterone profiles confirmed these findings. At day 18 post-mating, MEL and MEL+P4 groups exhibited significantly higher P4 concentrations (> 4.4 ng/mL) than the control group (0.73 ng/mL; P < 0.05), indicating enhanced luteal activity. In conclusion, melatonin combined with progesterone sponges proved to be a highly effective approach for advancing and synchronizing reproductive activity in Ouled Djellal ewes during the anestrous period, resulting in superior fertility and productivity outcomes compared with melatonin alone, Ovsynch, or no treatment.