The effects of an advanced uterine environment on embryonic survival in the mare

Abstract

The results emphasise the importance of an appropriate uterine environment for embryo growth and the inability of equine embryos to survive transfer to a uterus >2 days advanced even when luteostasis is achieved. It is possible that in normal, non-ET equine pregnancy, embryo-uterine asynchrony may account for some cases of embryonic death.

The period of the follicular phase during which the uterus of mares shows estrus-like echotexture influences the subsequent pregnancy rate

“…It is logical to surmise that the variation in the duration of the follicular phase with basal progesterone and high estradiol might affect the pattern of subsequent expression of endometrial genes related to embryo survival. In line with this hypothesis, a recent report clearly shows that pregnancy rate after transfer of embryos into recipient mares that had been under progesterone influence for longer than 2 days of the embryo's age was 0% [25]. Although the PGF treatment induces a fall in circulating progesterone less than 1 ng/mL between 24 and 36 hours after treatment [7], mares that ovulate soon after treatment will have had a relatively short period of basal progesterone and high estrogens compared with other mares having a longer ITO.…”

An Earlier Uterine Environment Favors the <i>In Vivo</i> Development of Fresh Pig Morulae and Blastocysts Transferred by a Nonsurgical Deep-uterine Method

“…Studies in other species have demonstrated that transferring embryos to a more advanced uterus can result in accelerated growth by increasing their rate of cell division [27, 28], which could fatally modify their subsequent development [4, 29] and adversely affect the pregnancy outcomes.…”

eCG concentrations, luteal structures, return to cyclicity, and postabortion fertility in embryo transfer recipient mares

“…These criteria were developed on the basis of the findings of a recent study which emphasized the importance of an appropriate uterine environment for embryo growth [41]. Equine embryos were unable to survive transfer to a uterus which has been under progesterone dominance for more than 2 days greater than the embryo's age [41]. A group of postaborted mares (group 3 category 2; n ¼ 7) had 1 to 2 consecutive anovulatory (LUF) cycles without signs of estrus.…”

“…The criteria for "reuse" an aborted recipient were that the mare had an ovulation or LUF after a well-defined estrous period with endometrial edema and with assumed basal level of progesterone. These criteria were developed on the basis of the findings of a recent study which emphasized the importance of an appropriate uterine environment for embryo growth [41]. Equine embryos were unable to survive transfer to a uterus which has been under progesterone dominance for more than 2 days greater than the embryo's age [41].…”