Influência do tratamento com estrógeno previamente a progesterona sobre a sobrevivência e desenvolvimento embrionário em éguas receptoras acíclicas

Abstract

The spread of embryo transfer in horses (ET) over the years resulted in an increasing of the demand for recipients, both for cyclic and acyclic mares in anestrus or transition. The first protocol used in acyclic mares had the purpose of mimic the uterine conditions of a cyclic mare in diestrus and was based only on the use of progesterone (P4), although later studies indicate that the previous application of estrogen can promote improvements in growth rates and embryonic survival. However, the influence of this greater exposure to estrogen, previously to P4, on embryo recovery and development in recipients is still uncertain. Therefore, the main objective of this study is to determine the effect of three hormonal protocols in acyclic mares on survival and embryonic development rates after ET. For this, the long estrus (LE) group has received 8 mg total of estradiol benzoate (EB) in increasing doses, remaining 7 days exposed to estrogen before the application of long-acting P4 (LA P4); the short estrous (SE) group received a single dose of 2.5 mg of EB two days before the administration of P4 LA; and the group without estrus (NE) started only 1500 mg of P4 LA. Donor embryos were collected eight days after ovulation, which were evaluated and transferred to recipients in the LE, SE and NE groups on day 4 after P4 LA application. Two days after ET, uterine lavages were performed in the recipients and were evaluated as embryo recovery rates, quality, and growth rate. It was observed that the LE group presented better rates of recovery and embryonic growth compared to the SE group. Consequently, it seems that the uterine environment is favorably influenced by along exposure to estrogen previously to P4, although no difference has been demonstrated between long or short previous exposure.