Cortisol levels, heart rate, and autonomic responses in horses during repeated road transport with differently conditioned trucks in a tropical environment.
Authors: Lertratanachai Siengsaw, Poochipakorn Chanoknun, Sanigavatee Kanokpan, Huangsaksri Onjira, Wonghanchao Thita, Charoenchanikran Ponlakrit, Lawsirirat Chaipat, Chanda Metha
Journal: PloS one
Summary
# Editorial Summary Equine professionals working in tropical regions have limited evidence on how road transport stress manifests in hot, humid climates, prompting researchers to investigate whether the physiological responses documented in temperate environments translate to these conditions. Six transport-experienced horses underwent repeated journeys in four truck configurations—air-conditioned trucks at full or reduced capacity, and non-air-conditioned trucks at full or reduced capacity—with cortisol sampling at baseline, 5, 30, and 90 minutes post-transport, alongside continuous heart rate and heart rate variability (HRV) monitoring. Only horses transported in non-air-conditioned trucks with reduced stocking density showed significantly elevated cortisol at five minutes post-transport, whilst all groups returned to baseline levels within 30 minutes, indicating that medium-distance transport in tropical environments produces minimal sustained stress in accustomed animals. Truck conditioning markedly influenced autonomic nervous system responses: air-conditioned full-load horses demonstrated parasympathetic dominance with decreased heart rates, whilst those in reduced-capacity air-conditioned trucks showed increased parasympathetic signalling and decreased sympathetic activity during transit. These findings suggest that for transport-experienced horses, environmental temperature control and stocking density significantly modulate acute physiological stress responses more than distance alone, offering practical guidance for tropical operations seeking to optimise welfare during routine journeys through appropriate vehicle investment and loading protocols.
Read the full abstract on PubMed
Practical Takeaways
- •Air conditioning and cargo loading significantly modify physiological stress responses during transport—non-air-conditioned trucks with reduced loading caused the highest cortisol spike, though recovery was rapid
- •Transport-experienced horses in tropical climates tolerate medium-distance journeys well; focus management efforts on truck ventilation and appropriate loading density rather than assuming all transport causes stress
- •Monitor heart rate variability and autonomic responses as markers of transport comfort; different truck conditions produce different autonomic profiles that may inform transport planning
Key Findings
- •Cortisol levels increased significantly only in non-air-conditioned trucks with space loads (N-ATS) at 5 minutes post-transport, returning to baseline by 30 minutes
- •Air-conditioned trucks with full loads (ATF) showed transient increases in beat-to-beat intervals and decreased heart rate during transport
- •Parasympathetic nervous system activity predominated during transport and immediately post-transport across all conditions
- •Transport-experienced horses showed minimal stress responses in tropical environment when transported in medium-distance journeys