Horse’s stress responses have been reported during road transport in temperate but not tropical environments. Therefore, this study measured cortisol levels, heart rate (HR), and heart rate variability (HRV) in horses during medium-distance road transport with different truck conditions in a tropical environment. Six horses were repeatedly transported in either air-conditioned trucks with full (ATF) or space (ATS) loads or non-air-conditioned trucks with full (N-ATF) and space (N-ATS) loads. Blood cortisol was determined beforehand and 5, 30, and 90 minutes post-transport. HR and HRV were assessed pre-transport and at 15-minute intervals until 90 minutes post-transport. Cortisol levels increased significantly in N-ATS horses (but non-significantly in ATF, ATS, and N-ATF horses) at 5 minutes post-transport and returned to baseline by 30 minutes post-transport. Predominant parasympathetic nervous system (PNS) activity was observed during the first few hours and returned to baseline until the destination was reached. A recurrent, increased PNS activity was detected post-transport. Interaction effects of air condition-by-loading condition-by-time, air condition-by-time, and separate effects of air condition and time were observed on HR and various HRV variables during transport. A transient increase in beat-to-beat intervals, coinciding with decreased HR, was observed in ATF horses. The PNS index increased, corresponding to a decreased sympathetic nervous system index, in ATS horses during transport. We suggest that medium-distance road transport causes no stress for transport-experienced horses in a tropical environment. Air and loading conditions impacted hormonal and autonomic modulation, causing different responses in horses transported in differently conditioned trucks.

Heart rate variability (HRV) is a frequently used indicator of autonomic responses to various stimuli in horses. This study aimed to investigate HRV variables in horses undergoing cold (n = 25) or hot (n = 26) shoeing. Multiple HRV variables were measured and compared between horses undergoing cold and hot shoeing, including the time domain, frequency domain, and nonlinear variables pre-shoeing, during shoeing, and at 30-minute intervals for 120 minutes post-shoeing. The shoeing method interacted with time to change the HRV variables standard deviation of RR intervals (SDNN), root mean square of successive RR interval differences (RMSSD), very-low-frequency band, low-frequency band (LF), the LF to high-frequency band ratio, respiratory rate, total power, standard deviation perpendicular to the line of identity (SD1), and standard deviation along the line of identity (SD2). SDNN, RMSSD, and total power only increased 30 minutes after hot shoeing (all p < 0.05). Triangular interpolation of normal-to-normal intervals (TINN) and the HRV triangular index increased during and up to 120 minutes after hot shoeing (p < 0.05–0.001). TINN increased only during cold shoeing (p < 0.05). LF increased 30 and 60 minutes after hot shoeing (both p < 0.05). SD1 and SD2 also increased 30 minutes after hot shoeing (both p < 0.05). SDNN, TINN, HRV triangular index, LF, total power, and SD2 were higher in hot-shoed than cold-shoed horses throughout the 120 minutes post-shoeing. Differences in HRV were found, indicating increased sympathovagal activity in hot shoed horses compared to cold shoed horses.

Strenuous exercise in traditional polo matches creates enormous stress on horses. Hematological and physiological measures may vary across different field-play positions. This study aimed to investigate the effort intensity and the impact of exertion on hematology and heart rate variability (HRV) in polo ponies with different positions. Thirty-two ponies, divided equally into eight teams, were studied. Each comprises forwards (number 1), midfielders (numbers 2 and 3), and defenders (number 4). Team pairs played the first chukka in four low-goal polo matches. Percent maximum heart rate (%HR_max), indicating ponies’ effort intensity, was classified into five zones, including zones 1 (95%). Hematological and HRV parameters were determined before, immediately after, and at 30-minute intervals for 180 minutes after chukkas; HRV variables were also obtained during warm-up and exercise periods. Results indicated that the number two ponies spent more time in zone 4 (p < 0.05) but less in zone 2 (p < 0.01) than the number four ponies. Cortisol levels increased immediately and 30 minutes afterward (p < 0.0001 for both) and then returned to baseline 60–90 minutes after exertion. Other measures (Hct, Hb, RBC, WBC, neutrophils, and CK enzyme) increased immediately (p < 0.0001 for all) and lasted at least 180 minutes after exertion (p < 0.05–0.0001). HRV decreased during the chukka until approximately 90 minutes afterward (p < 0.05–0.0001). The stress index increased during the chukka and declined to baseline at 60 minutes in number 1–3 ponies but lasted 90 minutes in those at number four. Effort intensity distribution differed among field-play positions. Decreased HRV indicated reduced parasympathetic activity during exercise, extending to 90 minutes after exertion in polo ponies. Defenders seem to experience more stress than those in other positions.

Single-confinement housing can pose welfare risks to domestic horses. This study investigated horses’ stress responses when confined to single stalls in different stable designs in a tropical savanna region to address a gap in the literature. In total, 23 horses were assigned to a stable with a central corridor and solid external walls (A) (N = 8), a stable with one side corridor and solid external walls (B) (N = 6), or a stable with a central corridor and no solid external walls (C) (N = 9). Air velocity, relative humidity, air temperature, and noxious gases were measured inside the stables, and the heart rate and HRV of the horses were also determined. The relative humidity was lower in stable C than in stable A (p < 0.05), while the air temperature was higher in stable C than in stable B (p < 0.05) during the day. The airflow and ammonia levels were higher in stable C than in stables B and A (p < 0.01–0.0001). Overall, horses’ HRV in stable A was lower than in those in stables B and C (p < 0.05–0.01). Horses in stable A tended to experience more stress than those in other stables.

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.

Changes in resting heart rate (HR) and HR variability (HRV) are utilised to assess training effects in horses. However, limited research has examined how these variables reflect training effects during exercise sessions and recovery periods, particularly in horses of different ages. This study investigated how HR and HRV changed during exercise sessions and recovery periods in untrained adult horses (UAHs; n = 9) and geriatric horses (UGHs; n = 9). HR and HRV were measured before and during a 54 min exercise bout over a 12-week training programme. Mixed-effects model with Greenhouse–Geisser correction was used for statistical analysis. The duration of elevated mean HR, sympathetic nervous system index, and stress index during the exercise sessions gradually decreased over the 12 weeks for both UAHs and UGHs. However, this decrease was faster in UAHs than in UGHs. Mean HR consistently decreased during the exercise sessions for both UAHs and UGHs over the 12 weeks. Furthermore, HRV returned to baseline faster in UAHs than in UGHs during the exercise bouts. These results indicate that the 12-week structured exercise programme positively influenced HR and HRV adaptation during exercise and recovery periods in UAHs and UGHs, with the adaptations differing dynamically between them.