Are Horses Stressed when Bitted for the First Time?

• Heart rate (HR) values were also recorded using a heart rate monitor at the same timepoints and during the bitting process.

The horses’ behaviour was also observed and assessed for the first minute after bitting and their stress responses were graded on a 1 to 5 scale using validated stress indicators. Behaviours were assessed ranging from 1 (very relaxed: jaw and lower lip relaxed, no bit or mouth movement, soft/slightly closed eyes) to 5 (very anxious: mouth open for extended periods, opening/closing repetitively, teeth grinding, eye whites visible).

The results were fascinating. Although heart rates showed a significant increase between the baseline and all other timepoints on Day 1, Day 2, and Day 3, no significant change was recorded in either eye temperature or observed behaviour after bitting over the three days.

While it was clear the introduction of a bit elicited a physiological stress response, the horses showed little indication in their observed behaviour that this was the case. The researchers warned that assessing a horse’s behaviour during the introduction of a bit may not give a true representation of the stress they are actually experiencing.

“Our results demonstrated the horses’ heart rate significantly increased from a baseline level compared to every other time point of measuring, including during, immediately post-bitting, then one and five minutes post-bitting,” says Brassington. “Whilst a heart rate change may be expected with a novel stimuli, this significant change occurred on each of the three consecutive days of bitting the horses and in the absence of other signs of stress.

“Previous literature has documented that physiological signs of stress, such as heart rate, do not always manifest in behavioural changes, which this current study concurs with. No significant differences were recorded in the behaviour grade scale applied to the horses during one minute post-bitting despite the increased heart rate, indicating a variety of behaviours may be expressed with some individuals masking a stress response. As such, we may need to consider using this technology further in our husbandry and equitation practices to inform our judgements of when to progress training.”

The researchers conclude that introducing the bit to a young horse can be a stressful procedure. Horses do appear to become accustomed to the process when it is performed regularly; however, the length of time needed for them to completely accept the bit is not yet known.

“Interestingly, the increase observed in heart rate did significantly decrease over the three days, as did the heart rate increase immediately post-bitting; collectively this provides indication of some habituation to the introduction of the bit during this short process,” explains Brassington. “As such, future research to determine complete habituation times over increased days would provide a more informed approach to this essential process in young horse training. Investigating alternative methods to introduce the bit, for example with the use of operant conditioning, may provide valuable informed approaches of habituating the horse to the bit. Similarly, applying other methods of quantifying physiological stress responses may lead to a valuable tool to support trainers in their assessment of horses during equitation.”