The lip twitch appears to be a more humane way of subduing a horse than an ear twitch, a new study suggests, provided it is not used for too long.
While the study found evidence supporting prior research about the analgesic (pain-killing) effects of the lip twitch – provided it was applied only for short periods – it found, in contrast, that the ear twitch appeared to subdue horses through pain.
Researcher Benjamin Flakoll set about analyzing the way in which the two forms of restraint subdued horses, noting that the mechanism of the ear twitch was not known.
Flakoll, whose findings were outlined in a poster presentation at the recent International Society for Equitation Science conference in France, conducted two experiments, the first involving 18 male horses – 10 stallions and eight geldings – divided into two groups.
The first group received the lip twitch while the second group received the ear twitch. He monitored heart rate and three heart-rate variability indices in his effort to determine autonomic nervous system activity before and during application of the twitches.
The autonomic nervous system has two main divisions – parasympathetic and sympathetic. The parasympathetic nervous system is part of the involuntary nervous system which controls, among other things, the heart rate, intestinal activity and glandular activity. The sympathetic nervous system governs an animal’s fight-or-flight response, often fueled by adrenaline.
A behavioral analysis was also performed to determine the ease with which horses could be handled before and after being twitched.
In the second study, 12 geldings were again split into two groups, with one group receiving the lip twitch and the other the ear twitch. In this experiment, levels of the stress hormone cortisol in the saliva were analyzed to assess stress levels before and after use of the twitches.
The results showed that the lip twitch led to significantly lower heart rates and changes in heart-rate variability indicating increased parasympathetic activity, when applied for five minutes, but significantly increased heart rates and heart-rate variability changes pointing to increased sympathetic activity when applied for longer periods.
Previous research on the lip twitch had examined the horses with the twitch applied for five minutes, only identifying the initial analgesic effect.
Flakoll’s findings of increased heart rate when the lip twitch is applied for more than five minutes offers new insight into the biological mechanisms at work.
Across both studies, 15 horses were assessed with the lip twitch and 15 with the ear twitch.
It was noteworthy that application of the lip twitch had no effect on the behavior of 14 out of 15 horses across both studies, indicating that even though stress levels appeared to increase when the lip twitch was applied for longer periods, it did not seem to cause pain.
The ear twitch led to significantly increased heart rates and changes in heart-rate variability indicating increased sympathetic activity, regardless of how long it was applied. Salivary cortisol levels rose significantly and made the horses more difficult to handle. Ten of 15 horses became more difficult to touch following the application of the twitch.
“It was concluded,” said Flakoll, “that the lip twitch initially subdues horses through a calming, probably analgesic effect, which may be reduced or eliminated when the twitch is applied for an extended period of time (for more than five minutes), while the ear twitch subdues horses through a stressful, probably painful effect.
“Due to these stark differences, only the lip twitch should be considered a humane method for subduing horses, while use of the ear twitch should be actively discouraged among veterinarians and people involved in equine management.”