Heart Rate and Heart Rate Variability Are Affected by Age and Activity Level in Athletic Horses

The physiological capabilities of horses begin to decline after they reach 15 years of age. However, some exceptionally talented horses can continue their sports careers beyond this age, raising concerns about their welfare. This study investigated animal welfare by observing resting heart rate (HR) and heart rate variability (HRV) metrics in geriatric horses participating in similar training or physical activities compared to younger adult horses over 30 min periods. Forty-six horses of varying ages and activity levels were divided into four groups, including horses under 15 years practising structured training for dressage (AL-1; N = 13) and school riding (AL-2; N = 13) and horses aged between 15 and 20 years participating in AL-1 (N = 10) and AL-2 (N = 10). In adult horses, the HR decreased in those performing AL-1, which was observed alongside an increased RR interval compared to those participating in AL-2 (p < 0.05 for both). Meanwhile, HRV increased in adult horses (measured by pNN50) but decreased in geriatric horses (measured by SDANN, SDNNI, DC, and SD2) participating in AL-1 when compared to their counterparts in AL-2 (p < 0.05 for all). Adult horses exhibited better autonomic regulation while engaged in structured dressage training than geriatric horses. These findings underscore the necessity for the careful management of physical activities to ensure the well-being of all horses, particularly older ones.