Embryo transfer in competition horses: Managing mares and expectations

Abstract

Embryo transfer (ET) is an accepted and successful technique for obtaining foals from mares without interrupting their competition careers. Recent research, however, suggests that the potential of factors including heat, exercise, repeated embryo flushing and repeated manipulation of the reproductive cycle using exogenous hormones to have a negative impact on fertility may have been underestimated. This paper reviews the evidence base for involvement of these factors in repeated failures to recover embryos from nongeriatric competition mares without obvious clinical or pathological indications of reproductive abnormalities. It concludes that, for some mares at least, a cessation of exercise for the periovulatory period and the period between ovulation and embryo flushing, combined with careful management of flushing-induced endometritis, and minimal hormonal manipulation of the reproductive cycle, may be necessary to optimise embryo recovery rates. Mare owners may have been encouraged to request ET for their mares following high-profile examples in the media of elite mares that have produced foals by ET whilst competing. The veterinarian should educate mare owners about the multiple factors that may affect the chances of recovering an embryo from their mares, and should manage the expectations of mare owners so that they do not approach ET programmes in the expectation that there will be no disruption to their training and competition plans.

Synchronization of cyclic and acyclic embryo recipient mares with donor mares

“…Embryo transfer is an assisted reproductive technique used to maximize the number of offspring from mares with a desired phenotype, or as a tool to circumvent health or reproductive dysfunction (e.g., chronic orthopedic issues, recurrent embryonic loss, or severely fibrotic endometrium), or to obtain foals from fillies or mares with an active athletic career (Squires et al, 1999;Panzani et al, 2007;Campbell, 2014;McCue and Squires, 2015). The success of an embryo transfer program is affected by multiple factors, such as the management and fertility of dams and sires, experience of the professional(s) collecting and transferring embryos, and quality and management of recipient mares (Squires et al, 1999;McKinnon et al, 1988;McCue and Squires, 2015).…”

Factors Affecting Recipients' Pregnancy, Pregnancy Loss, and Foaling Rates in a Commercial Equine Embryo Transfer Program

“…Several donor's, embryo's, recipient's and technical factors have been analyzed to assess their effect on recipients pregnancy. Evaluated donors' factors have been age, intrinsic fertility and sport activity [7][8][9][10][11][12][13][14], while embryo factors were age, quality and developmental stage [2][3][4][15][16][17][18].…”

Assisted reproductive techniques in mares

“…The main limitations of embryo transfer as an equine ART are that (a) recovery of embryos requires that the donor mare have a functional tract, at least to the point that sperm can reach the oviduct, the mare ovulates normally, and the oviduct and uterus can support fertilization and development of the embryo until Day 7 or 8 after ovulation; (b) breeding the donor mare requires a full insemination dose of good‐quality semen; and (c) superovulation of mares is problematic (Squires & McCue, ), so only the potential embryo resulting from ovulation of the one dominant follicle (or sometimes two, if the donor mare spontaneously double‐ovulates) is available. Use of ET in mares in competition can be complicated by the effects of stress (Campbell, ), and repeated manipulation of the mare's uterus (breeding, uterine flush) can be associated with induction of endometritis (Campbell, ).…”