Exogenous melatonin improves resumption of ovarian function in undernourished ewes during anestrous season in Argentina.

CHAVES, M.A.; FRANCO, C.A.; MARTINEZ, D.; MIAZZO, A.J.; VAZQUEZ, M.I.*

Congreso; XXII CONGRESSO BRASILEIRO DE REPRODUCAO ANIMAL (CBRA); 2017

The main factors that influence reproductive performance of sheep are reproductive seasonality and nutritional condition, particularly in the central region of Argentina, where the availability of food is highly seasonal. Melatonin treatment is an effective method for inducing estrous cycles, increasing ovulation and improving embryo viability during anestrus. On the other hand, undernutrition can compromise follicle-oocyte competence, luteal function and embryo development. Therefore, the effect of exogenous melatonin on ovarian function in undernourished ewes during anestrous season in Argentina was investigated. In October, 24 adult ewes (weighed 51.2±2.1 kg, body condition scored (scale 1-5) 2.65±0.16, mean±SEM) housed in an open barn at the Río Cuarto University facilities (30º07´S, 64º14´W), were assigned into two groups: treated (MEL) or not with a subcutaneous implant of melatonin (Melovine®, CEVA). They were kept under natural photoperiod. After 40 days, both groups were synchronized with intravaginal pessaries and eCG (400 IU) and fed to provide 1.5 (Control, C) or 0.5 (Low, L) times daily maintenance requirements. Therefore, ewes were divided into four groups (n=6): C, C+MEL, L and L+MEL. Estrus detection was performed twice daily and at estrus (Day=0) ewes were mated. At Day 15, a second estrus detection and mated was performed. Ovulatory follicles from Day -5 to ovulation were monitored daily by transrectal ultrasonography with a real time, B mode and rigid 7.5 MHz linear-array transducer. The day of ovulation was detected by collapse of a large follicle. Pregnancy diagnosis was determined at Day 28 after estrus. Statistical comparisons of proportional values were based on the Chi-squared Test. The level for statistical significance was set to P < 0.05. After 21 days, groups L and L+MEL had an average weight loss of 5 kg (P