Survival of Day-4 embryos from young, normal mares and aged, subfertile mares after transfer to normal recipient mares

Abstract

The estimated embryonic loss rate between Days 4 and 14 after ovulation for young, normal mares (9%) was significantly lower (P less than 0.01) than the estimated embryonic loss rate for aged subfertile mares (62%). Fertilization rates, which were based on the recovery of embryos at Day 4 after ovulation, were 96% and 81% (P less than 0.1) for normal and subfertile mares, respectively. Day-4 embryos were collected from the oviducts of normal and subfertile donors mares. These embryos were transferred to the uteri of synchronized, normal recipient mares to test the hypothesis that the high incidence of embryonic loss in subfertile mares was related to embryonic defects. The hypothesis was supported because embryo survival rates were significantly higher (P less than 0.05) for Day-4 embryos from normal compared to subfertile mares. These defects may have been intrinsic to the embryo or might have arisen due to the influence of the oviducal environment before Day 4 after ovulation.

The effect of mare's age on multiple ovulation rate, embryo recovery, post-transfer pregnancy rate, and interovulatory interval in a commercial embryo transfer program in Argentina

“…Furthermore, it is expected that embryos that degenerate during early development are unable to complete oviductal transit and are not recovered. In this regard, the PR of Day 4 embryos collected from the oviduct of aged subfertile mares did yield a lower PR than early embryos of young mares (Ball et al, 1989). Perhaps in the latter study, if embryo recovery would have been delayed for an extra 5 days (Day 9), the subsequent transfer might have yielded a higher PR.…”

Pregnancy loss during the embryonic period

“…Transfer of embryos from normal mares to normal and subfertile recipients resulted in similar pregnancy rates, indicating that the uterus of a subfertile mare may be capable of supporting an embryo from a normal mare . Embryos collected from the oviducts of normal and subfertile donors and transferred to normal recipients resulted in lower pregnancy rates for mares receiving embryos from subfertile donors than for mares receiving embryos from normal donors (Ball et al 1989). …”

“…The high rate of embryonic loss in yearling mares has been attributed to immaturity, inadequate nutrition or physical stress (Mitchell and Allen 1975). Older mares have a lower pregnancy rate and a higher loss rate compared with younger mares (Ball et al 1989). The effect of advanced age, however, is difficult to separate from acquired subfertility and is confounded by the effect of parity since the two are generally correlated.…”

Maternal age and in vitro culture affect mitochondrial number and function in equine oocytes and embryos

“…Embryos flushed from the oviducts of mares $20 years of age have been reported to undergo delayed cleavage and to contain fewer cells than those from younger mares (Carnevale and Ginther 1995), analogous to the situation in older compared with younger women (Baird et al 2005). Combined with studies demonstrating that embryos from mares .18 years show lower survival rates than embryos from mares ,6 years after transfer to young recipients (Ball et al 1989), this indicates that the loss of developmental potential is intrinsic to the ovulated oocyte or arises during very early (intra-oviductal) embryo development. Further studies have clearly demonstrated that the principal contributor to the age-related decline in mare fertility is reduced oocyte quality, because oocytes from mares $15 years often exhibit morphological abnormalities associated with functional deficiencies that, in turn, contribute to a decrease in developmental competence (Carnevale and Ginther 1992;Carnevale 2008;Altermatt et al 2012).…”