Melatonin treatment in winter and spring and reproductive recovery in Sarda breed sheep

This study aimed to evaluate the effect of melatonin treatment carried out between late winter and early spring on reproductive response in Sarda breed sheep and whether the photo-refractoriness can influence this reproductive response. The study was conducted on 3200 adult ewes, aged 3-6 years old, with body condition score (BCS) 2.5-4.0, from 16 commercial sheep farms in Northern Sardinia. In each farm 200 animals were enrolled and subdivided into 2 groups (n = 100 each): Group M (treated with one 18 mg melatonin implant), and group C (untreated). The melatonin treatments were performed on 10th February; 10th March; 10th April and on 10th May each time in 4 different randomly selected farms. Adult males, treated with 3 melatonin implants 1 week before females, were introduced in each flock 35 days after ewes' treatment, and removed after 45 days of cohabitation with females. Pregnancy was determined by transabdominal ultrasonography examination between 45th and 90th day after ram introduction. Data showed that melatonin treatment increased the fertility rate significantly (P < 0.05), with the higher fertility rate in the ewes treated in April and May. The average time in days from male introduction to lambing was shorter in treated than in control ewes (P < 0.05). Further, at the 160th and 170th day after male introduction the group M showed a higher number of lambed ewes compared to C (P < 0.01). This effect was observed at 180th and 190th days after ram introduction, also, but with lower significance (P < 0.05). In conclusion, melatonin treatment improved reproductive efficiency and advanced breeding season in Sarda sheep, especially when ewes were treated in spring.