Effects of Short-Term Melatonin or Progestogen with Gonadotropic Treatments on Reproductive Performance, Hormonal Levels and Ovarian Activity of Ewes

Abstract

The study compares the effects of short-term application of melatonin alone with a commonly used progestogen + gonadotropin on the reproductive performance, serum hormone concentrations, and ovarian activity of Improved Wallachian sheep. To induce ovarian cyclicity, 382 ewes were allocated into two treatment groups. Ewes of treatment group 1 (n=26) received dietary melatonin (5mg/head/day) for 18 days. Ewes of treatment group 2 (n=356) received intravaginal sponges (FGA, flugestone acetate 20mg) for 12 days followed by injection of eCG (equine chorionic gonadotropin, 500IU i.m.) at the time of sponge withdrawal. Forty-eight hours after sponge or melatonin withdrawal, sheep were exposed to rams, and recorded reproductive performance. Six ewes from each group were selected for hormone assessment and their ovaries removed for histological analysis. Ewes receiving melatonin had lower fertility, fecundity, smaller follicles (0 – <1mm), and lower follicular atresia compared to group 2. In addition, the concentration of progesterone and IGF-I, ovulation rate, and the number of healthy follicles were increased compared to FGA+eCG-treated ewes. Our results indicate that short-term application of melatonin is effective in inducing ovarian cyclicity in ewes with an increased ovulation rate despite low fertility and fecundity.