Yes, horses are sensitive to the bit, but there are aversive behaviours

The position of the handler during the experiment. To determine the resultant force to which the horse's nose or mouth was subjected, left and right rein tension values were added.
The position of the handler during the experiment. To determine the resultant force to which the horse’s nose or mouth was subjected, left and right rein tension values were added. Rein tension values indicated in the picture are examples only. Photo: Eisersiö et al.

Horses are considerably more sensitive to rein signals delivered through a bit than a conventional fabric halter, researchers have found, but there was also clear evidence of their dislike for the mouthpiece.

Marie Eisersiö and her colleagues noted that rein tension will vary continuously in synchronicity with the horse’s gait and stride when a rider maintains contact on the reins.

“This continuous variation makes it difficult to isolate the rein tension variations that represent a rein tension signal, complicating interpretation of rein tension data from the perspective of horse-rider interaction,” the study team noted in the journal Frontiers in Veterinary Science.

In their just-published study, they investigated the characteristics of a rein tension signal for backing and the response of horses to it, comparing pressure from a bridle and snaffle bit familiar to the horse, or by the noseband which comprises part of a halter.

Their research involved 10 healthy warmblood horses, aged 4 to 15, who were fitted with a rein tension meter.

Each of the horses, who usually work in dressage or jumping, was trained to step back in the aisle of a stable.

For the videoed experiment, the handler stood next to each horse’s withers, applying tension on the flat leather reins until the horse stepped back, with various parameters and behaviours monitored.

This was repeated eight times with the bridle and eight times with the halter.

They found that inattentive behavior was significantly more common in the halter treatment and in young horses, compared with the bridle treatment and adult horses.

Evasive behaviors with the head, neck, and mouth were significantly more common in the bridle treatment than in the halter treatment. The occurrence of head/neck/mouth behaviors increased with increasing rein tension and duration of the rein tension signal.

Horses that were looking at or investigating something, turning toward the handler, or had their head up or forward and mouth open, always took significantly longer to respond to the rein tension.

“When controlling for behavior, the horses responded significantly faster and to a lighter rein tension signal in the bridle treatment than in the halter treatment,” the authors said.

Some horses even responded before tension was applied, when the reins were picked up. This happened 18% of the time.

“These results suggest that the bridle was perceived as more aversive by the horses, since they showed more of these evasive and resistance behaviors during the rein tension signals applied with the bitted bridle compared with the halter,” they said, noting that horses may also associate different equipment with different activities.

“Inattentive behaviors were significantly more common in the halter treatment and in young horses, indicating that young horses, in particular, may have associated the halter with non-training time and thus their attention was more on other things than on paying attention to rein tension signals.

“Interestingly,” they continued, “there was no significant difference between young and adult horses in magnitude of rein tension or response latency.”

There was, however, a tendency for the young horses to respond faster and to a lighter rein tension signal. This indicates that the adult horses had perhaps become habituated to the rein tension signal to some extent and were thus less responsive.

The study team said it should be borne in mind that when escalating pressure signals are used as a means of communication, there is always a risk of causing the horse discomfort, pain, and even physical injury.

“Bridles with bits and bitless alternatives both press on sensitive structures of the horse’s head and mouth when rein tension is applied,” they said, noting that mouth injuries connected to the use of bridles are common.

“Scrutinizing the characteristics of rein tension signals may thus yield clues to improving horse welfare during training and riding, ultimately increasing awareness of signals and how the horse perceives these.”

It is likely, they said, that horses would benefit from riders learning to use negative reinforcement in a more sophisticated way, for example, by reducing the magnitude of rein tension signals, being more prompt in releasing rein tension, and recognizing how little rein tension is actually needed to elicit a response.

The study team comprised Eisersiö, Anna Byström, Jenny Yngvesson and Agneta Egenvall, all with the Swedish University of Agricultural Sciences; Paolo Baragli, with the University of Pisa in Italy; and Antonio Lanata, with the University of Florence, also in Italy.

Eisersiö M, Byström A, Yngvesson J, Baragli P, Lanata A and Egenvall A (2021) Rein Tension Signals Elicit Different Behavioral Responses When Comparing Bitted Bridle and Halter. Front. Vet. Sci. 8:652015. doi: 10.3389/fvets.2021.652015

The study, published under a Creative Commons License, can be read here

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