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Quantitative evaluation of behavioral and physiological adaptation during retraining of retired Thoroughbred
Sung Jun An1, Jong Hwan Lee2, Hwan Yong Lee3
1Department of Artificial Intelligence, Cheju Halla University, Jeju 63092, South Korea.
Background:
Retired Thoroughbred racehorses commonly transition into riding roles, yet outward behavioral calmness may not fully reflect internal physiological regulation, with implications for safety.
Objectives:
To quantify behavioral and autonomic adaptation across repeated startle exposures and assess concordance between behavioral and physiological indicators.
Methods:
Twelve retired Thoroughbreds underwent standardized plastic-bag startle trials conducted across three sessions (T1-T3), each including pre-training (Before) and post-training (After) phases, with three repeated exposures at 5-minute intervals, both before and after a three-month retraining program. Behavioral responses were scored using a 0-4 behavioral score (BS) and physiological responses were measured via heart rate (HR) and response duration (RD). Adaptation patterns were analyzed using Friedman tests, nonlinear exponential decay modeling, linear mixed-effects models and vector-based similarity analyses.
Results:
All indicators decreased significantly across repeated exposures, consistent with initial habituation followed by stabilization. The largest changes occurred between the first and second sessions. HR decreased more rapidly than BS, suggesting faster physiological adaptation, whereas BS declined gradually. Pre- versus post-training comparisons showed reductions in BS, HR and RD. Similarity analyses demonstrated strong coupling between HR and RD trajectories, while BS showed variability.
Conclusion:
Behavioral and physiological indicators followed coordinated but temporally distinct adaptation trajectories. Faster physiological stabilization, reflected by HR, appeared to precede full behavioral stabilization, indicating that physiological recovery may not be fully captured by behavioral observation alone. Reliance on a single indicator may inadequately represent retraining progress and combined behavioral and physiological measures may provide a comprehensive assessment of adaptation in retired Thoroughbreds.
