Putting a twitch on a horse’s upper lip to restrain him or allow an unpleasant procedure to be performed is sometimes controversial. But how does a twitch work — and is it just a matter of hurting the horse so his attention is diverted from the clipping or injection?
Vets in Michigan took eight young Arabian horses that had never been twitched or clipped. They stood them in a familiar grooming area with a calm, older horse that they knew, so that they were not anxious about being alone. Their heart rates and the variability of their heartbeats were measured; these are a reliable indicator of stress and pain.
The plan was to clip the inside of their ears. Half were clipped without a twitch and half with, before the groups were reversed for the other ear. Later, within two hours, all the horses were twitched a second time and the clippers were applied to their ears.
The results were clear: heart rate and beat variability were far greater in the horses clipped without twitches. Some could not be clipped at all without a twitch.
This suggests that the twitch genuinely calmed the horses and reduced their fear and stress when the clippers came up to their ears. When they were twitched for a second time, their hearts were almost as steady as the readings taken before any clipping was attempted.
The horses did not appear to have become fearful of the twitch or to have remembered that it was either painful or stressful — and they had learned, to some extent, that ear clipping was not going to hurt. The vets concluded that twitching a horse for a short time is not painful or cruel, but emphasise that a twitch is no substitute for proper, reward-based training.
Ref Horse & Hound; 12 October 2017