Twin management in the mare: A review

Abstract

Twin gestation in the mare is undesirable and can have disastrous consequences. As in many cases, the key to success in twin management lies in a thorough follow‐up and accurate recording of clinical findings in the pre‐breeding examination. A pregnancy diagnosis in the mobility phase is imperative for a good outcome in the event of twin reduction. If a twin gestation is not diagnosed during this early pregnancy stage, several other procedures exist for managing post‐fixation twins (>16 days) with varying degrees of success. Most twin pregnancies are the result of multiple ovulations (dizygotic twins). However, monozygotic twins are also sporadically diagnosed, due to the increasing number of transferred in vitro produced equine embryos. In these cases, the most optimal treatment strategy still needs to be determined. This review provides an overview of the various twin reduction techniques described with the expected prognosis as well as of some less reported techniques with their results. In addition, physiological events and the reduction techniques are demonstrated to the user in virtual 3‐dimensional illustrations.

Advances in equine reproduction

“…twins originating from separate ovulations/oocytes) in the mare, a significant number of twins escape early resolution, for various reasons. Peere et al 12 discuss the existing options for intervention, and describe the decision-making process involved in choosing between conservative management (e.g., waiting for spontaneous resolution in the case of day 16-40 adjacent vesicles) or deciding to intervene using one of the techniques described for manually or otherwise disrupting a vesicle, embryo or foetus; this decision-making process necessarily incorporates knowledge of the optimal stages of gestation to perform the various interventions, and the live singleton foal rates that can be expected. More detailed information about two specific procedures for resolving post-fixation twins is provided in case series about transvaginal ultrasound-guided aspiration (TUA) 13 and transrectal foetal thoracic compression.…”

“…A review of the techniques for managing twin or multiple pregnancy 12 emphasises that, while early detection (before conceptus vesicle fixation at day 16) and manual crushing of supernumerary vesicles is the preferred method for managing dizygotic multiple pregnancy (i.e. twins originating from separate ovulations/oocytes) in the mare, a significant number of twins escape early resolution, for various reasons.…”

“…The fact that foetal death does not always result after the first attempt at compression emphasises the need to warn the mare owner that a single attempt is unlikely to be sufficient, and to make sure that the manipulated foetus is positively identified (by relative location, or foetal sex if this differs) so that it can be reidentified for repeat treatment. Both Arnold et al 14 and Peere et al 12 further warn that reduction of monozygotic/monochorionic (identical; derived from a single conceptus vesicle) twins is almost invariably unsuccessful irrespective of the technique used, presumably as a result of intimate vascular or placental connections. Until a reliable technique can be developed for selective reduction of monochorionic twins, of which the vast majority arise from in vitro produced embryos, 15 early induction of luteolysis to terminate the pregnancy before the establishment of endometrial cups (i.e., before day 35) is the recommended approach.…”