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Breeding

What to do and when: management of equine twin pregnancies

02 March 2024
Clinical
10 mins read
02 March 2024
Volume 8 · Issue 2

Abstract

The use of ultrasound to diagnose pregnancy early in the mare, has aided veterinarians' ability to identify twins before fixation, allowing manual reduction to be performed with the highest success rate of delivering a single live foal. Unfortunately, when pregnancy diagnosis is delayed and dizygotic or monozygotic twins are identified post-fixation, the success rates of a normal-sized healthy foal decreases. Depending on the stage of gestation different procedures have varying degrees of invasiveness, and live foaling rates. These options may include manual and natural reduction, transvaginal ultrasound-guided reduction, oscillation, thoracic compression, cranio-cervical dislocation, transcutaneous ultrasound-guided injection and induction of abortion. Manual reduction prior to fixation has the highest success for the birth of a normal-sized single foal. Oscillation and thoracic compression are less invasive than procedures later in gestation and appear to have the best success rate before 65 days with cranio-cervical dislocation a better option later in gestation. Early identification of twins allows for determination of the optimum procedure for reduction, increasing the chances of the birth of a normal-sized individual foal.

The establishment and loss of twins often results in a mare that is barren for a year and the associated economic loss for the owner. The incidence of twin births has been documented as occurring in 1–2% of the equine population (Ginther, 1979), with twinning accounting for 6–30% of abortions in the mare (Jeffcott and Whitwell, 1973; Roberts, 1986; Giles et al, 1993). When twins are present, gestation proceeds normally until the conceptuses begin to compete for endometrial contact area to optimise uteroplacental nutritional exhange. The death or compromise of one fetus affects the remaining fetus, initiating changes in placental hormones leading to premature mammary gland development. Subsequent abortion due to placental insufficiency occurs between 5–9 months of gestation (Roberts, 1982). If abortion occurs after the eighth month, the mare's fertility may be affected negatively the following year. Fortunately, with the use of ultrasound there is better understanding of the mechanisms involved in twinning, earlier identification and improved approaches to twin reduction (Chevalier and Palmer, 1982; Simpson et al, 1982; Bowman, 1987).

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equine twins
twin reduction
dizygotic twins
monozygotic twins