Likelihood of pregnancy after embryo transfer is reduced in recipient mares with a short preceding oestrus

Abstract

The likelihood of pregnancy in recipient mares is positively correlated with the duration of endometrial oedema during the oestrus preceding ET. This suggests a role for an adequate duration of oestrogenic priming during oestrus on uterine receptivity and embryo survival.

Synchronization of cyclic and acyclic embryo recipient mares with donor mares

“…This previous study also demonstrated that only mares showing uterine edema ≥2 (similar to the grading used herein) became pregnant (Souza et al, 2015). Again, this finding is consistent with the Utrecht's study demonstrating that duration of uterine edema is important for normal pregnancy rates in embryo transfer recipient mares (Cuervo-Arango et al, 2017). In the present study, recipients mares with a fresh ovulation (< 5 days) had improved uterine features scores when a second dose of prostaglandin F2α was given (G8).…”

“…Though, mares with fresh ovulation (< 5 days) receiving one dose of prostaglandin (G7) had lower uterine edema scores during estrogen treatment and had remarkably lower conception rates compared with other groups. A recent study out of the Netherlands, demonstrated that pregnancy rate is positively correlated with the duration of uterine edema during estrous prior to the embryo transfer (Cuervo-Arango et al, 2017). Our findings in hormonally manipulated embryo recipient mares supports the claim by the Dutch group that showed that uterine edema is important for normal establishment of pregnancy in embryo recipient mares.…”

“…Reported synchronization protocols may involve the use of prostaglandin F2α (i.e., dinoprost tromethamine) or its analogs (e.g., sodium cloprostenol), steroid hormones (progestins and estrogens), and ovulation induction agents such as human chorionic gonadotropin and GnRH agonists (e.g., deslorelin acetate, histrelin) (Carnevale et al, 2000;McCue et al, 2002;Rocha Filho et al, 2004;Carnevale et al, 2005;Caiado et al, 2007;Fleury et al, 2007;Greco et al, 2008;Greco et al, 2012;Kaercher et al, 2013;McCue and Squires, 2015;Greco et al, 2016;Pinto et al, 2017). Prostaglandin F2α alone is commonly used in cyclic mares to bring them back into estrus when necessary (Cuervo-Arango et al, 2017). Whereas, a combination of estrogen (e.g., estradiol 17β, estradiol benzoate, or estradiol cypionate) and progestin (e.g., altrenogest, or progesterone) is typically used in acyclic and transitional recipient mares or when there is a shortage of recipient mares, demanding a tight-synchrony between one embryo donor and one or two of its recipients (Rocha Filho et al, 2004;Greco et al, 2012;McCue and Squires, 2015;Silva et al, 2017;Pinto et al, 2017).…”

Equine embryo research ethics – should we worry?

“…The work presented in the papers of Ortiz-Escribano et al [1] and of Perez Marin et al [2] had been granted ethical approval in accordance with the policies of the local institutions, and of this journal. Nonetheless, these papers provide examples of 1) embryos being deliberately sacrificed for experimental purposes and 2) embryos being transferred using techniques which have a significantly lower survival rate than that usually achieved following transfer of in vivo produced embryos which have not been cryopreserved [3,13]. Notwithstanding the fact that the law seems to offer no protection to equine embryos per se, this gives one pause for thought about whether loss of or damage to them should nonetheless be a cause for ethical concern.…”

“…Two papers are published in this issue of Equine Veterinary Journal which involve the production of equine embryos using cryopreservation of either oocytes or embryos [1,2] whilst a third examines outcomes achieved in embryo transfer in clinical practice [3] and a fourth reports in vivo experiments addressing placental adaptions to fetal growth [4]. Equine embryos are defined as being less than 42 days of gestational age.…”