Objective: To determine the effect of colic surgery on return to function in Thoroughbred racehorses, identify clinical variables associated with successful return to racing, and compare racing performance between horses undergoing colic surgery and an untreated cohort.
Design: Retrospective cohort study.
Animals: 59 Thoroughbred racehorses 2 to 5 years of age that underwent colic surgery and survived to hospital discharge and 90 untreated Thoroughbred racehorses equivalent in class.
Procedures: Medical records of patients evaluated for colic between January 1996 and July 2009 were reviewed, and horses with a Jockey Club Information Systems record were included. Physical examination and laboratory findings on hospital admission, lesion location and type, duration of surgery, duration of hospitalization, and any postoperative complications were recorded. The untreated cohort comprised 2 untreated horses randomly selected from runners in each treated horse's last race immediately prior to the date of colic surgery. Records were obtained from the Jockey Club Information Systems in April 2011. Only horses that raced at least once before and after surgery were included in the performance analysis. Number of starts, earnings per start, and total earnings were determined from race records for all horses. Quarterly earnings and number of starts for 12 quarters following the date of surgery were compared between treated and untreated horses via a Wilcoxon rank sum test. Longevity of racing was assessed by means of survival analysis. Poisson regression was used to compare rates of return to racing and active quarters aggregated across the first 12 quarters after surgery and for the available follow-up period for treated and untreated horses.
Results: 45 of 59 (76%) horses that raced prior to surgery returned to racing. Return to racing was significantly associated with admission heart rate and blood lactate concentration. From quarters 3 to 12, treated and untreated horses had slight differences in the number of starts but no difference in earnings per quarter. Treated and untreated horses had no difference in total number of quarters raced, number of starts, or earnings after surgery. Treated horses had higher earnings per start, compared with untreated horses.
Conclusions and clinical relevance: In the present study, racing Thoroughbreds that underwent colic surgery and successfully returned to racing had no differences in performance variables, compared with their untreated cohorts.