Twitching as a form of horse restraint has been used for many years. There are many ways to twitch a horse, though the most common areas used are the horse’s lips and ears. While the process of twisting a horse’s lips or ears so they will stand still may sound barbaric, in some cases – such as a medical emergency – it is necessary.
In 2017 a study conducted by Benjamin Flakoll and associates  investigated the lip and ear twitch to understand how they work and what effect they have on the horse’s wellbeing. They measured the horse’s heart rate, heart rate variability (HRV) and salivary cortisol levels to determine whether twitching has a calming, analgesic effect on horses, or if it inflicts stress and pain . They found that the lip twitch caused a decrease in heart rate for 5 minutes, after which the heart rate increased . However, the ear twitch significantly increased the horse’s heart rate and cortisol levels which did not decrease with time . This suggests that the ear twitch causes a pain and stress reaction within the horse. The lip twitch causes the horse to relax, however, this only lasts for around 5 minutes before it becomes more of a pain reaction.
Another study conducted within the same year  assessed lip twitching and the effect that it had on young horses who were getting their ears clipped for the first time. As you may imagine, clipping a horse’s ear hair is not usually an enjoyable experience for the horse, and so a comparative study was done to see whether using a lip twitch during the procedure would be beneficial for horses and trimmers . The study found that the lip twitch significantly minimised the horse’s behavioural reactivity as well as a reduction in the horse’s heart rate closer to within baseline parameters . The lip twitch was more successful during the second session .
Both of these studies suggest that lip twitching does seem to have a relaxing, analgesic effect on horses, though this reaction only lasts for a certain amount of time before the twitch causes the horse pain and stress. Ear twitching, on the other hand, seems to only cause negative effects within the horse.
As the research suggests, horse’s experience a calming, relaxed reaction to a lip twitch. But how is that the case? I couldn’t imagine having the same reaction if someone twitched my lip, and I know some horses who would blow a gasket if someone tried to pat their nose, let alone put a twitch on it.
A study by Evert Lagerweij and associates  found that the twitch works in a similar way to modern acupuncture. It stimulates the mechanoreceptors in the skin which activates the pain-decreasing mechanism within the horse’s body . They claim that part of the reason that acupuncture works is due to the release of endorphins that occurs during the procedure, which was also found within the horse’s blood shortly after the twitch was applied . Therefore, twitching the horse’s nose does seem to have a similar effect to that of modern acupuncture, though as Flakoll and associates found, this effect may only last a short while before wearing off.
While in some situations it seems that twitching harms the horse’s wellbeing, it is important to remember that sometimes situations require the use of this form of restraint. Horses can be dangerous animals and while we try to do our best to train them, a severely distressed horse may not listen to commands, no matter how much training they have received. The evidence suggests that nose twitching is better for your horse than ear twitching, however, I understand that sometimes an ear twitch is the safest and best thing an owner or specialist can do, for horse and human.
 Flakoll, B, Ali, A & Saab, C 2017, ‘Twitching in veterinary procedures: how does this technique subdue horses?’, Journal of Veterinary Behaviour, vol. 18, pp. 23 – 28
 Ali, A, Gutwein, K & Heleski, C 2017, ‘Assessing the influence of the upper lip twitching in native horses during an aversive husbandry procedure (ear clipping)’ Journal of Veterinary Behaviour, vol. 21, pp. 20 – 25
 Lagerweij, E, Nelis, P, Wiegant, V & van Ree, J 1984, ‘The twitch in horses: a variant of acupuncture’, Science, vol. 225, pp. 1172 – 1174