Evaluation of postsale endoscopy as a predictor of future racing performance in an Australian thoroughbred yearling population

Introduction Upper airway endoscopy of thoroughbred (TB) yearlings is commonly used in an attempt to predict laryngeal function (LF) and its impact on future race performance. The aim of this study was to determine if different grading systems and laryngeal grades were correlated with future performance. Materials and Methods Postsale endoscopic recordings were obtained from an Australian TB yearling sale during a four-year period from 2008 to 2011. Horses were included if they had a diagnostic postsale video endoscopic recording and raced within Australia. Recordings were graded using the Havemeyer system and subsequently recategorised according to the Lane scale and two condensed scales. Performance data were sourced from Racing Australia and comparisons were made between groups. Results A total of 1244 horses met the inclusion criteria. There were no significant differences in sex or sales price between groups. There were no significant differences in the number of starts or wins between groups for any grading system. For the condensed Havemeyer scale, horses with intermediate LF were separated into two groups. Significant differences in earnings were found between 'normal' and 'abnormal' (P = 0.02) and 'intermediate-low' and 'abnormal' grades (P = 0.03). There were no significant differences between horses with 'intermediate-high' and 'abnormal' grades (P = 0.40). No significant differences were found between the two intermediate grades (P = 0.60) or between horses with normal LF and either 'intermediate-low' or 'intermediate-high' grades (P = 0.99). Discussion Resting LF in Australian yearling TBs assessed using a condensed Havemeyer grading scale had some predictive value for future racing performance. This information should be considered when performing yearling endoscopic examinations.