Associations between Medical Disorders and Racing Outcomes in Poorly Performing Standardbred Trotter Racehorses: A Retrospective Study

SIMPLE SUMMARY: Many subclinical medical disorders are considered as possible causes of decreased performance in racehorses. The present study aims to evaluate the associations between different disorders diagnosed in 248 poorly performing Standardbreds and their racing outcomes in the periods of time around hospitalization and their lifetime careers. In particular, the effects of respiratory, cardiovascular, gastric, and muscular conditions on number of starts, wins, placings, and earnings were investigated. Inflammation of the lower airways was associated with worse racing results in the periods before and after hospitalization and with a shorter and less successful career, confirming its role in performance impairment. Other conditions negatively influencing short-term racing outcomes included dynamic obstructions of the upper airway and gastric ulcers, while the role of exertional rhabdomyolysis was not clear. Finally, exercise-induced pulmonary hemorrhage and cardiac arrhythmias did not seem to affect Standardbred trotters’ performance. ABSTRACT: Poor performance in racehorses is commonly associated with subclinical diseases. This study aims to evaluate the associations between medical disorders and racing results in Standardbred trotters. The clinical records of 248 poorly performing Standardbreds were retrospectively reviewed, and their racing results were extracted from an online database, concerning the periods 3 months before and 6 months after hospitalization and the entire lifetime. Generalized linear models were used to evaluate the effects of different disorders on racing outcomes. Airway neutrophilia was associated with limiting lifetime starts and wins pre- and post-hospitalization, while mastocytosis was associated with less wins in the post-hospitalization period. Therefore, lower airway inflammation showed both short- and long-term impacts on racing performance. Severe upper airway obstructions and gastric ulcers showed associations with less placings in the post-discharge period but no long-term influence on performance. The significance of exertional rhabdomyolysis was indeterminable, yet interference with the number of starts in the post-discharge period was reported and associated with lower total career earnings. Exercise-induced pulmonary hemorrhage and cardiac arrhythmias were not associated with worse racing outcomes: therefore, their role in poor performance remains unclear.