Synchronization Protocols in Spanish Merino Sheep: Reduction in Time to Estrus by the Addition of eCG to a Progesterone-Based Estrus Synchronization Protocol

Abstract An appropriate management of reproduction allows ewes to breed at a more intensive rhythm, more compatible with economic efficiency of farms. Hence, the objectives of the present work were to evaluate a traditional estrus synchronization protocol (based on medroxyprogesterone acetate-impregnated intravaginal sponges combined or not with equine chorionic gonadotropin) on a Merino sheep herd during the breeding season, in order to determine the best working protocol for this breed. A total of 277 sheep, blocked by age (200 ewes and 77 ewe lambs) were randomly allocated to four groups, two of ewes (E and Ee) and two of ewe lambs (L and Le). All females received 60 mg MAP (medroxyprogesterone acetate) sponges on the first day. At the day of removal the animals of groups Ee and Le received 450 IU of eCG (equine chorionic gonadotropin). Mean estrus synchronization rate was 92.06% and similar among groups. Time to estrus was shorter for Ee (46.93±12.44 h) and Le (44.34±10.76 h), when compared to treatments without eCG (60.60±20.46 h and 58.68±17.72 h for E and L, respectively; P<0.05 for both). Pregnancy rates were 71.35 and 72.86% for ewes and ewe lambs, respectively, and similar among groups. Lambing rates were lower in ewes (1.36) than in ewe lambs (1.85) with no significant effect of eCG. The study demonstrates the efficacy of the synchronization method with MAP and the reduction in the time to estrus induced by eCG in Spanish Merino ewes and ewe lambs during the breeding season.