Factors influencing foaling rate following colic surgery in pregnant Thoroughbred mares in Central Kentucky.
Authors: Drumm N J, Embertson R M, Woodie J B, Ruggles A J, Hopper S A, Fimmers R, Handler J
Journal: Equine veterinary journal
Summary
# Factors influencing foaling rate following colic surgery in pregnant Thoroughbred mares Whilst clinical experience has long suggested that gestational age affects pregnancy viability after colic surgery, evidence supporting this relationship has been limited. Researchers at Rood and Riddle Equine Hospital reviewed 228 pregnant Thoroughbred mares that underwent colic surgery between 1993 and 2007, recording variables including age, gestational stage, duration of pre-operative colic, haematocrit, surgical findings, anaesthetic duration, and intra-operative complications, with foaling success confirmed by Jockey Club registration. The study found that 66.7% of mares produced live foals post-operatively; critically, mares bred at least 40 days before surgery had significantly better outcomes (69.8% live foal rate) compared to those in earlier gestation (<40 days: 48.7%), alongside improved prognosis in mares aged 15 years or younger and those with shorter pre-operative colic duration. For practitioners managing colic emergencies in pregnant stock, these findings provide concrete prognostic indicators—younger mares presenting beyond 40 days of gestation carry substantially better odds for maintaining viable pregnancies through to term, information that directly informs both clinical decision-making and owner counselling regarding surgical intervention versus medical management.
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Practical Takeaways
- •When counselling owners about prognosis for colic surgery in early pregnancy (<40 days gestation), expect roughly 50% live foal rate; this improves to ~70% if mare is beyond 40 days gestation
- •Older mares (>15 years) have reduced foaling success after colic surgery—factor this into pre-operative prognostication and owner discussions
- •Duration of colic before surgery matters—longer colic duration before intervention correlates with worse foaling outcomes, reinforcing the urgency of prompt surgical referral in pregnant mares
Key Findings
- •66.7% of pregnant mares (152/228) had a live foal registered after colic surgery
- •Mares bred <40 days before surgery had significantly lower foaling rates (48.7%) compared to those ≥40 days post-breeding (69.8%, OR=0.41, P=0.012)
- •Foaling rate was significantly influenced by mare age (P=0.008) with better outcomes in mares ≤15 years
- •Duration of colic signs before surgery significantly affected foaling rates (P=0.03)