Risk factors for post‐partum colic in a population of <scp>UK</scp> and Irish Thoroughbred broodmares

BACKGROUND: Broodmares are at increased risk of gastrointestinal colic. However, colic risk factors specific to this population have not been investigated. OBJECTIVE: To investigate horse- and management-level risk factors for post-partum colic in a cohort of Thoroughbred broodmares in the United Kingdom and Ireland. STUDY DESIGN: Prospective, nested case-control study. METHODS: Twenty-nine Thoroughbred stud farms in the United Kingdom and Ireland were recruited, and 1044 mares were followed over the 2021 and/or 2022 foaling seasons. Data were collected on signalment, medical and management history for post-partum colic mares and matched (3:1) controls. Multivariable analysis was conducted using conditional logistic regression. RESULTS: Due to strong collinearity between days post-partum and time spent stabled, two multivariable models were built. Days post-partum (Model 1: OR 0.9, 95% CI 0.8-0.9; p < 0.001) and increasing hours stabled (Model 2: OR 1.2, 95% CI 1.1-1.3; p < 0.001) were strongly associated with increased risk of post-partum colic. Colic risk was highest immediately post-partum, with reduction in likelihood of colic up to 50 days after foaling. NSAID use in the previous 28 days (Model 1: OR 6.2, 95% CI 2.0-65.5; Model 2: OR 4.1, 95% CI 1.1-15.0; p = 0.048) and a history of previous colic (Model 1: OR 7.4, 95% CI 1.2-7.9; Model 2: OR 5.3, 95% CI 1.7-17.1; p = 0.01) were also associated with increased colic risk. Calcium supplementation was associated with increased likelihood of post-partum colic in Model 1 only (OR 4.4, 95% CI 1.3-15.7; p = 0.04). MAIN LIMITATIONS: Mares comprised a small sub-population of UK and Irish Thoroughbred broodmares. Pre-partum colic was not investigated. CONCLUSIONS: Maximising turnout in post-partum broodmares may reduce colic risk, immediately post-partum and up to 50 days. Broodmares who have recently received NSAIDs, have a history of colic or are receiving a calcium-based supplement may be at increased risk of post-partum colic.