The effect of insertional suspensory branch desmitis on racing performance in juvenile Thoroughbred racehorses

Limited information exists regarding the prognosis for juvenile racehorses sustaining injury to the suspensory ligament branch insertion (JISBI).

To investigate the effect of JISBI on racing performance; and to assess whether the severity of JISBI is prognostically important.

Retrospective cohort study.

Records were reviewed for 896 juvenile Thoroughbreds in training, to identify horses with JISBI limited to one branch (cases). The ability of cases to start a race was compared to their cohorts. Race records of maternal siblings were compared to cases.

The prevalence of JISBI for this population was 9.5%. Cohorts were 3.2 times more likely to start as a 2-year-old and 3.6 times more likely to start as a 3-year-old compared to horses with JISBI. Of 58 cases that were compared to maternal siblings, the total earnings per start (EPS), 2- and 3-year-old EPS were all reduced (P<0.01). Cases raced a mean of 3.8 times compared to 7.4 races for controls over the study period and were 113.2 days older by the time of first start (P<0.01). 'Speed figures' and EPS were, however, similar between cases that had raced and controls. Cases with a moderate-severe lesion (≥ Grade 2) were at significantly greater risk of reinjury than mild cases (P<0.05).

JISBI causes decreased racing ability as a 2-year-old. Mild cases perform similarly to controls by their 3-year-old season, but more severe cases demonstrate reduced ability as a 3-year-old, with an increased likelihood of reinjury. Although the wastage was higher in case horses with JISBI, individual cases that make it to a race have similar earnings per start as their controls.