OC9 Effect of Melatonin Implants in Guirra Ewes

Abstract

This study assessed the effect of melatonin implants (18 mg) on the fertility and prolificacy in adult sheep (47) and ewe lambs (22) in Guirra breed during the seasonal anestrus (April–May). Sixty nine ewes were divided in four groups: adult sheep and ewe lamb and treated or not with melatonin implants. Thirty days after melatonin implant insertion, all ewes were synchronizer with intravaginal progestogen pessaries (30 mg fluorogestone acetate) for 12 days. Ewes were injected with 400 IU PMSG intramuscularly when pessaries were removed. Artificial inseminations (AI) were carried out after oestrus synchronization (54 ± 1 h) and 6 days later males were introduced into the flock. To determine cyclicity in the ewes after treatment, blood was collected from all ewes 10 days after withdrawn pessaries and progesterone concentration was measured by RIA. The ewes were considered cyclic if their plasma progesterone concentration was >1 ng/ml. The main findings from this study were: (i) the percentage of ewes cycling was similar between experimental groups (95.7%) and (ii) Fertility at parturition, prolificacy and lamb weights observed in control group (57.9%, 1.2 ± 0.09 lambs and 3.7 ± 0.22 kg; n = 19) and melatonin group (58.0%, 1.0 ± 0.15 lambs and 3.9 ± 0.31 kg; n = 50) were similar. Lamb weight differed between adult sheep and ewe lambs (4.3 ± 0.19 kg vs 3.4 ± 0.31 kg, respectively; p < 0.05). Our results suggest that melatonin treatment do not improve reproductive parameters in the Guirra breed.