Effect of melatonin and melatonin plus progestagen protocols on some reproductive performance and blood parameters at the beginning of the breeding season in Hasmer ewes

The aim of this study was to investigate the effect of exogenous melatonin administered by different methods at the beginning of the breeding season on estrus onset, fertility, plasma progesterone and malondialdehyde (MDA) concentrations in Hasmer ewes. To this end, the ewes were divided into three groups: Group I (MEL): This group received subcutaneously 18 mg melatonin implant (RegulinTM, Ceva– Turkiye) Group II (MELPRO): This group received subcutaneously 18 mg of melatonin implant (RegulinTM, Ceva–Turkiye), followed by the intravaginal administration of a sponge containing 20 mg of flugestone acetate (Choronogest CRTM–France) for a period of 9 day. This was followed by the intramuscular injection of 250 µg of cloprostenol (SenkrodinTM– Vetas–Turkiye) as soon as the sponge was removed. Group III designated as the control group (CON), received 1 mL of saline was administered subcutaneously for placebo effect. Estrus was detected using teaser rams starting 24 h after the melatonin (Group MEL), PGF2α (Group MELPRO) and physiological saline (Group CON) applications twice a day (06:00 and 17:00). Ewes in oestrus were moved to separate compartments and mated with fertile rams. Blood samples were collected from the vena jugularis on the day of treatment initiation, on the day of mating, and on day 17 of gestation. Pregnancy examinations were performed between 25 and 30 days after mating, and heartbeats were monitored using a 5–8 MHz linear trans–rectal probe in the groups (DP 50 VETTM, Mindray Ltd. China). There was no statistical difference in the onset of first oestrus between the groups (P>0.05). A noteworthy finding was the increase in progesterone concentration on the 17th day of pregnancy in the group treated with melatonin alone, compared to other groups, at the beginning of the breeding season (P<0.05).