Horse pain caused by the bit refers to the various painful sensations of varying intensity and duration that horses may experience from the use of a bit during riding, due to poor adaptation of the equipment to their morphology or excessive stress. These pains are frequently associated with oral lesions, particularly in the corners of the mouth, interdental spaces, premolars and tongue. Rarely visible from the outside, for example through hemorrhage, these lesions receive little attention. Pain and lesions are accompanied by fear and anxiety in the animal. They potentially concern all horses wearing a bit manipulated by a human being via reins, whether mounted or harnessed, in particular by the application of great tension in these reins.
The animal's suffering due to bits is often ignored by both horse-riding and driving enthusiasts, not least because of habituation to behavioral signals of oral pain in horses, which are mistakenly passed off as normal. This phenomenon is known as bit-blindness. Researchers and veterinarians involved in this field recommend regular checks to ensure that there are no serious injuries in the horse mouth or labial commissures.
General
Pain management in horses
Like all mammals, the horse has a conscious experience of pain, which it seeks to avoid in favor of comfort. This sensation of pain is triggered by a noxious stimulus. Pain then acts as a warning system to minimize tissue damage. As horses are flighty animals, their reaction to pain stimuli will typically be to flee the source. This pain will generate associated anxiety and fear.
Bit usage
When riding and driving, the horse is required to wear a bit in its mouth, connected to reins. The bit is often invasive for the animal. The setup of the bit and the forces exerted by the reins play a crucial role in the oral health and comfort of ridden or harnessed horses. The snaffle bit rests on the corner of the mouth. The palate or tongue bit acts on the palate, the upper wall of the mouth. The bit ring is in contact with the corner of the mouth. Finally, the bit's barrel rests in all cases on an interdental space between the incisors and molars, made up of jawbones covered by a mucous membrane, the "bar". The horse tongue passes under the barrel of the bit. According to Guillaume Henry, when a modern bit is correctly fitted (without excessive tightening of a noseband or chain) and inert, it causes no particular pain, any pain being the result of the action of the rider's hands on the reins connected to the bit. The bit has been standard equestrian equipment for millennia, generally considered indispensable and ethically justified.
Problems caused by the bit
The problem of the pain caused by the bit is linked not only to the horse welfare, but also to its sporting performance, as even slight discomfort can cause the animal to concentrate on its pain rather than its performance. Historically, there have been some very painful bits, for example with spiked barrels and central articulated bridges that can pierce the palate. Some modern bits are associated with more lesions: long shank bridle bits in Icelandic horses, Crescendo bits, straight non-articulated mullen bits and straight plastic bits in trotters.
While bits have been used on horses since the Bronze Age, the pain and injuries they can cause have only recently been studied scientifically, particularly in the late 2010s. As recently as 2005, there was no data available on how horses behave during painful experiences with their bits. As the differences between the rating scales used by the authors of the publications made it difficult to compare results, veterinary surgeon Dr. Kati Tuomola (University of Helsinki) and her colleagues created a lesion measurement scale in 2019 to facilitate the creation of statistics in subsequent studies.
Painful areas
The whole of a horse's mouth is sensitive to pain. Wearing the bit stimulates numerous sensory receptors, particularly those in the interdental space, tongue, labial commissures and buccal mucosa. The interdental space (the bar) is particularly sensitive. The bite stimulates nociceptors mediated by the trigeminal nerve in the lips, tongue, teeth and bones. The gum is the periosteum, the most sensitive part of the bone. The horse's oral mucosa consists of stratified squamous epithelium (mucosal epithelium) and underlying connective tissue, called the lamina propria. This oral mucosa is densely innervated to monitor all substances entering the horse's mouth, the entry point to its digestive system.