Racing performance of juvenile Thoroughbreds with femoropatellar osteochondrosis at auction: a retrospective case-control study

Abstract

Background: Osteochondrosis (OCD) is common in the femoropatellar joint in Thoroughbred yearlings for sale at auction and there is no consensus on the effect on racing outcomes. Objectives: Describe femoropatellar OCD in juvenile Thoroughbreds and compare the racing performance of affected Thoroughbred horses to siblings and unaffected horses from the same sale. Study design: Retrospective case-control study of juvenile horses born between 2010 and 2016. Methods: Radiographic reports from 27 Thoroughbred auctions of weanling (5-11 months of age) and yearling (12-22 months of age) horses were reviewed to identify femoropatellar OCD. Age and sex of cases and controls were obtained from the sales catalog. Subject racing performance was obtained from an online database and compared to sibling controls and age- and sex-matched hip controls from the same sale using the Kruskal-Wallis test. Results: Femoropatellar OCD was identified in 429 horses with North American race records. OCD was present on 519 lateral trochlear ridge (LTR) and 54 on medial trochlear ridge (MTR). The length and depth of OCD lesions was similar for LTR and MTR lesions. There were more males in the subject group (70%) than in sibling controls (47%). Subject racing performance was compared to 1,042 sibling and 757 hip controls. There was no significant difference between cases and both control groups for ever starting, years raced, total starts, starts for 2-5 years of age, total placings or placings at 2-5 years of age. Analysis of specific lesion metrics revealed weak correlations for some performance outcomes (both positive and negative) resulting in an inability to draw firm conclusions. Main limitations: Retrospective observational study where management techniques were unknown, and buyer directed case selection may introduce bias.