Duration of continuous fetal gastrointestinal peristalsis before parturition in mares maintained at a breeding farm or in a university hospital

Gestation length is not a reliable indicator of fetal maturity due to the variability of normal gestation length in the mare. A standard method to accurately predict equine fetal maturity is not being used clinically. The presence of continuous gastrointestinal peristalsis, as detected ultrasonographically, is an indicator that both human and canine fetuses are mature (can survive after elective cesarean section). To determine if continuous gastrointestinal peristalsis, which we termed Phase 5, was a valid indicator of fetal maturity in the horse, and whether this indicator varied in late-gestation mares in the potentially stressful environment of a veterinary hospital, the motility of the fetal gastrointestinal tract was evaluated ultrasonographically in mares managed extensively on a breeding farm and those hospitalized in a university teaching hospital. Our hypotheses were that, due to stress, hospitalized mares would have a longer gestation length and more days in Phase 5 than would mares foaling in their home environment. When adjusted for sex of the foal, the marginal model-adjusted mean of gestation length (marginal mean: 353.6; 95 % CI: 351.0–356.1 days) of mares foaling at their home breeding farm was not significantly different than that (345.5; 95 % CI: 336.8–354.2 days) of mares foaling in the hospital, thus our hypothesis regarding gestation length was not supported. Phase 5 fetal gastrointestinal peristalsis was present in all cases before parturition. The duration of Phase 5 in fetuses of hospitalized mares (marginal mean: 17.6; 95 % CI: 13.1–22.0 days) was greater than that for mares foaling at the breeding farm (marginal mean: 10.7; 95 % CI: 9.0–12.5 days), supporting our hypothesis regarding the length of Phase 5. The presence of continuous fetal gastrointestinal peristalsis can be a useful indicator that parturition is impending in the mare. This information may aid in making decisions in managing high-risk equine pregnancies. More research is required to determine how soon after Phase 5 commences the fetus is mature enough to survive induction of parturition or cesarean section.