Factors influencing foaling rate following colic surgery in pregnant Thoroughbred mares in Central Kentucky.

Reasons For Performing Study: Clinical experience has suggested that foaling rates following colic surgery in the pregnant mare are influenced by days of gestation. This premise has not been supported in previous studies. We also aimed to determine the effects of other potential influencing factors.

Objective: To determine the influence of age of gestation on foaling rates in pregnant mares following colic surgery and evaluate the relationships between other factors and foaling rates.

Methods: Medical records of Thoroughbred mares, which had colic surgery performed from 1993 to 2007 at the Rood and Riddle Equine Hospital, were reviewed. Mares identified in the record as pregnant or bred within the previous 15 days were included in this study. Age of the mare, date of surgery, gestational age, duration of colic at admission, packed cell volume at admission, surgical diagnosis, duration of general anaesthesia, intraoperative hypotension, intraoperative hypoxaemia and post operative signs of endotoxaemia were recorded. A mare was considered to have a live foal if that foal was registered with the North American Jockey Club.

Results: Of the 228 mares, where pregnancy had been confirmed, 152 (66.7%) had a live foal registered after surgery. Mares bred <40 days before surgery had a lower foaling rate compared with mares undergoing surgery ≥40 days after breeding: 48.7% vs. 69.8% (odds ratio [OR] = 0.41 [95% confidence interval (CI) 0.20-0.83], P = 0.012). Foaling rate was also influenced by mare's age (P = 0.008) and duration of colic signs before surgery (P = 0.03).

Conclusions: The prognosis for a live foal after colic surgery in the pregnant Thoroughbred mare is significantly better if the mare is ≤15 years of age and ≥40 days of gestation.

Potential Relevance: The results of this study are useful for clinicians offering a prognosis for a live foal following colic surgery in pregnant mares.