Greater concentrations of IGF-1 are associated with increasing pregnancy rate in melatonin implanted anestrous Barki ewes

•Reproductive seasonality in sheep presents a major constraint for production.•Melatonin-CIDR-eCG protocol alleviates the reproductive seasonality in ewes.•Melatonin administration manipulates the hormonal profile of P4, E2, T3 and IGF-1.•Increasing IGF-1 associated with melatonin in improving pregnancy in ewes. The present study was conducted to determine if increases in IGF-1 concentration, associated with treatment of ewes with melatonin, has beneficial effects on pregnancy rates when there is induction of estrus in anestrous ewes. A total of 120 multiparous lactating ewes were assigned to three groups (n = 10/group). Ewes of Group 1 were treated with a melatonin implant for 42 days followed by insertion of a controlled internal drug release (CIDR) device for 14 days with administration of equine chorionic gonadotropin (eCG) at day of CIDR removal. The ewes of Group 2 were treated with a CIDR and eCG at the same times as ewes of Group 1 and ewes of Group 3 were assigned to an be untreated control group. Melatonin implantation resulted in an increase in IGF-1 concentrations and lesser estradiol (E2) and triiodothyronine (T3) concentrations. Ewes of Groups 1 and 2 had the greatest progesterone (P4) concentration compared ewes of Group 3. The E2:P4 ratio was less in ewes of Group 1 compared Group 3. Melatonin implantation of ewes resulted in a greater pregnancy rate compared to treatment with the CIDR and eCG which, in turn, had a greater rate than ewes of the control group. In conclusion, melatonin implantation modulates the hormonal milieu including P4, E2, T3 and IGF-1 in seasonally anestrous ewes. Increased IGF-1concentrations, as a result of melatonin treatment, are associated with a greater percentage pregnancy rate when there is treatment of anestrous ewes to induce onset of estrus.