Reproductive success in Thoroughbred broodmares post large colon resection or colopexy.

Objective: To describe reproductive performance in Thoroughbred broodmares post-large colon resection and to compare to performance post-colopexy.

Study design: A single-institution retrospective study.

Animals: A total of 29 client-owned horses: post-large colon resection (LCR) n = 19, post-colopexy: n = 10.

Methods: Thoroughbred broodmares that survived until discharge following LCR (Group R) or colopexy (Group P) between 2006 and 2023 were included. Clinical data were collected from clinical records. Breeding and foaling data were collected from the Australian and New Zealand Studbooks. Statistical analysis were performed using Mann-Whitney U and Fisher's exact test using R software. Descriptive and postoperative reproductive data were compared between groups and a calculated nationwide average.

Results: There were no differences in any evaluated measurements of reproductive success between groups. In Group R, the first breeding season post-resection appeared less successful than the second (p = .03 [95% CI: 0.026-0.98]) or third (p = .03 [95% CI: 0.018-0.93]); however, these differences were not statistically significant after Bonferroni correction for multiple comparisons (adjusted significance threshold p < .0083) and were not observed when unserved mares were excluded. Both groups achieved similar live foal/mare served percentages when compared to Racing Australia's published data (Group R: 60.5%, Group P: 68.2%, Racing Australia: 64.3%).

Conclusion: No difference in reproductive success post-surgery was noted between techniques. Reproductive success is achievable post-large colon resection.

Clinical significance: Postoperative reproductive success should not be a factor in intraoperative decision-making when determining which preventative strategy (LCR or colopexy) is utilized. Further larger studies are required to confirm these findings and investigate possible initial reduction in reproductive success post-LCR.