Retrospective analysis of post-mortem findings in Thoroughbreds aged from birth to 18 months presented to a UK pathology laboratory.

Enhanced understanding of reasons for, and timings of, mortality in Thoroughbreds prior to entering race training is warranted to provide insight into this population's health status. The aims of this study were to describe pathologies diagnosed at post-mortem (PM) examination in Thoroughbreds aged from birth to 18 months and investigate associations between age and pathology. Reports from a pathology laboratory in Newmarket, UK, were used to identify eligible cases examined between January 2006 and December 2020. Reported pathologies were extracted and categorised where appropriate. Comorbidities and pathogens identified were reported where available. Associations between age and selected pathologies were assessed using logistic regression. Of 144 eligible Thoroughbreds presented for PM, 137 had an available report and pathologist's diagnosis. Congenital defects were most commonly reported (20%; n = 28/137; 95%CI 15–29), 69% of which (n = 19/28; 95%CI 49–82) were conformational manifestations of developmental orthopedic disease (DOD). Pneumonia was an important pathology (14%; n = 20/137; 95%CI 36–53) during the pre-weaning period, where Rhodococcus equi was identified in 50% (n = 10/20; 95% CI 29–70) of cases. Odds of congenital defects (OR 56.6; 95%CI 7.0–460.0; P < 0.001) were significantly greater in horses aged 0–2 days compared to 4–18 months at PM. Odds of pneumonia (OR 4.3; 95%CI 1.1–1.7; P = 0.04) were significantly greater in horses ages 1–4 months compared to 0–2 days at PM. This study shows that conformational manifestations of DOD are an important contributor to perinatal mortality, and that pathologies reported at PM vary with age in young Thoroughbreds. • Post-mortem findings from young Thoroughbreds are described. • The majority of cases presented in the neonatal period. • Congenital limb defects were an important contributor to perinatal mortality. • Rhodococcus equi was an important pathogen, particularly in pre-weaning pneumonia. [ABSTRACT FROM AUTHOR]