Cortisol release, heart rate and heart rate variability, and superficial body temperature, in horses lunged either with hyperflexion of the neck or with an extended head and neck position.

This research investigates whether forcing a horse’s head and neck into a state of hyperflexion – a position commonly used in equestrian sports – is a stressor for the animal. The researchers used measurements of salivary cortisol concentrations, heart rate, heart rate variability, and superficial body temperature to try and identify stress responses in horses under two conditions: one, with their head and neck in an extended position; and two, with their head and neck in hyperflexion. The findings suggest that, in these conditions, hyperflexion alone doesn’t cause acute stress in horses.

Methodology and Experimentation

• The research involved 16 horses which were subjected to two treatment methods on two separate days. The order of the treatments was randomized between horses.
• On ‘day A’, the horses had their heads and necks fixed in side reins in a position that allowed forward extension. On ‘day B’, their heads and necks were fixed in a position of hyperflexion.
• The physiological responses of the horses were assessed by measuring specific indicators associated with stress – salivary cortisol concentrations, heart rate, heart rate variability (HRV) and superficial body temperature.

Results

• Results showed that cortisol concentration increased in response to lunging (an exercise method for horses) on both days, but there was no significant difference between ‘day A’ and ‘day B’ conditions.
• Similarly, there was a decrease in beat-to-beat (RR) interval as a response to lunging on both days, but again, no significant difference between the two day conditions.
• The same was true for HRV variables standard deviation of RR interval (SDRR) and RMSSD (root mean square of successive RR differences).
• The only noticeable difference between the two day conditions was found in the cranial region of the neck, where the difference between maximum and minimum temperature increased when the horse was in hyperflexion.

Conclusion

• The findings suggest that the hyperflexion of the head alone does not trigger an acute stress response in horses when lunged at a moderate speed and not touched with the whip.
• However, the study concludes that if hyperflexion is combined with active intervention of a rider, it may lead to a stressful experience for the horse, indicating that further research in these conditions is needed.