Horse pain caused by the bit

 

Like all mammals, the horse has a conscious experience of pain,^[1] which it seeks to avoid in favor of comfort.^[2] This sensation of pain is triggered by a noxious stimulus.^[3] Pain then acts as a warning system to minimize tissue damage.^[3][4] As horses are flighty animals, their reaction to pain stimuli will typically be to flee the source.^[3] This pain will generate associated anxiety and fear.^[5]

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.^[6] 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.^[7] The snaffle bit rests on the corner of the mouth.^[8] The palate or tongue bit acts on the palate, the upper wall of the mouth.^[8] 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".^[8][9] The horse tongue passes under the barrel of the bit.^[8] 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.^[10] The bit has been standard equestrian equipment for millennia, generally considered indispensable and ethically justified.^[4]

 

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.^[3] Historically, there have been some very painful bits, for example with spiked barrels and central articulated bridges that can pierce the palate.^[11] 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.^[12]

While bits have been used on horses since the Bronze Age, the pain and injuries they can cause have only recently been studied scientifically,^[4] particularly in the late 2010s. As recently as 2005, there was no data available on how horses behave during painful experiences with their bits.^[13] As the differences between the rating scales used by the authors of the publications made it difficult to compare results,^[14] 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.^[14]

 

The whole of a horse's mouth is sensitive to pain.^[10] Wearing the bit stimulates numerous sensory receptors, particularly those in the interdental space, tongue, labial commissures and buccal mucosa.^[1] The interdental space (the bar) is particularly sensitive.^[9] The bite stimulates nociceptors mediated by the trigeminal nerve in the lips, tongue, teeth and bones.^[15] The gum is the periosteum, the most sensitive part of the bone.^[15] The horse's oral mucosa consists of stratified squamous epithelium (mucosal epithelium) and underlying connective tissue, called the lamina propria.^[16] This oral mucosa is densely innervated to monitor all substances entering the horse's mouth, the entry point to its digestive system.^[16]

Cook and Kibler compare the horse's suffering to that caused when the barrel of a pencil presses against the gums of a human being.^[15] Pinching the edge of the tongue between the bit and the bone is also painful, as is stretching the lips longitudinally to twice their normal length under the retracting effect of the bit.^[15]

Mouth pain caused by biting results from tissue compression, laceration or stretching, inflammation and impaired blood circulation.^[17] The repeated rubbing or impact of the bit can cause bruises, cuts, tears and ulcers in the horse's mouth.^[18] Swelling and bleeding bars can cause a horse to try to slide its tongue over the bit.^[8] Sudden action on the reins always causes the animal severe pain.^[19] A particularly painful situation is when the bit rests on the molars, without the support of the corners of the mouth or the tongue.^[8]

Cook and Kibler compared the behavior of 66 horses with and without a bit, using a questionnaire sent to riders who had switched from a bit bridle to a bitless bridle. They found a reduction in pain signals in 65 of the 66 bitless horses, with an average of 87% fewer pain signals;^[20] however, the results of this study are limited by sampling bias.^[2]

 

According to various authors of scientific publications, oral lesions caused by bit-wearing are "common".^[21][22][23]

In 2008, Tell and colleagues studied Swedish horses ridden with a bit, concluding that ulcers near the first and second premolars and corners of the mouth are caused by the bit and bridle, uninfluenced by the teeth-floating routine.^[24] Odelros and Wattle examined the mouths of 144 Standardbred trotters in 2018, and found that 88% had mouth lesions.^[25]

Uldahl and Clayton examine the outer corners of the mouth of Danish eventing horses after a competition in 2019, with the inside of the mouth not examined: six (7.5%) of 80 horses and one (3%) of 33 ponies have external lesions.^[26] The study by Tuomola and colleagues, carried out on 261 trotting horses examined in Finland after a race (2019), shows that 84% of these horses have lesions in the bit area, of which 21% are mild, 43% moderate and 20% severe lesions according to the assessment scale proposed by these authors.^[22] In the bit area, 70% of horses showed bruising and 40% wounds.^[27] About 2% of horses showed visible mouth bleeding at the end of the race, and 5% of bits examined showed blood when removed.^[22] The authors also conclude that the absence of blood outside the mouth does not exclude the existence of serious injuries inside.^[22] Injuries are often observed in horse racing, whether pre-existing, acquired or aggravated by such racing, probably due to the very nature of these competitions: harnessed horses are controlled exclusively with reins and bits, with great potential tension being exerted via these reins.^[3]

A study carried out by the Finnish team on horses and ponies after a cross-country event in 2021 concluded that injuries were more frequently observed in warm-blooded horses than in ponies.^[21] Mares are also at greater risk of lesions than geldings.^[21] Of all horses, 52% (109/208) showed acute oral lesions in the bit area, mild in 22% (45/208), moderate in 26% (55/208), and severe in 4% (9/208).^[28] No bleeding was observed outside the mouth, with only one horse bleeding inside.^[29]

 

A comparison of bit and bitless horses shows that lesions at the corner of the mouth are only present in horses that regularly wear a bit.^[16] The comparative study by Mata et al. between polo ponies and racehorses concludes that racehorses with a snaffle bit have a significantly higher prevalence of commissure lesions and a higher rate of ulcerations than polo ponies with a bridle bit.^[12][16]

Regular contact with the bit at the commissure of the outer lips leads to more or less marked depigmentation, which may result from prolonged pressure or previous inflammation, inhibiting melanocyte function.^[28] Such depigmentation is therefore characteristic of old, repeated lesions.^[27] They are more frequently observed in eventers than in trotters.^[30]

About 26% of trotters examined by Tuomola et al. in 2019 had injuries to the mandibular bars,^[16] compared with 31% of Icelandic horses examined by Björnsdóttir et al.in 2012.^[16]

The bit causes knocking on highly innervated, and therefore highly sensitive, teeth. Firstly, against the incisors when the bit is put in and taken out. ... The passage of the bit is directly subject to pain or apprehension of pain. ... The bit meets the wolf's teeth. These are small teeth called first premolars, positioned in front of the second large premolars in the upper jaw and the bars in the lower jaw. ... When they come into contact with the bit, these teeth become hypersensitive due to daily knocking, and cause lesions.^[31]

These lesions are generally located close to the maxillary teeth; those in the area of the lower second premolar are reputed to be difficult to detect.^[16][32] Periostitis (formation of bone spurs) often forms in the bar of domestic horses, with erosion of enamel and dentin, whereas these lesions do not exist in wild horses that have never worn a bit.^[32]

A few oral injuries may be due to sharp tooth enamel, but the majority are attributed to the use of the bit and equestrian equipment, an action on the reins connected to the bit causing the mucous membrane to slide over the horse's teeth with increased pressure.^[16] Medium-sized articulated bits are associated with a lower risk of mandibular injury than non-articulated bits.^[30] It is possible that over-tightening of the noseband or other equipment on trotters can press the mucous membranes against the teeth and contribute to mandibular injuries. Tightening of the noseband is associated with lesions of the outer corner of the mouth.^[26]

 

The horse tongue is highly sensitive, and therefore vulnerable to injury.^[33][34] The main cause of lingual injuries in horses is the bit.^[33]

When the vascularity of a horse tongue is compromised by its tack, the tongue changes color.^[35]

Dr. Jacques Laurent identifies three possible forms of vascularization changes in the horse's tongue:

• arterial compression alone, which gives the tongue a white color ;
• venous compression, which turns the tongue blue and swollen; and
• a mixed form, which is also the most frequent.^[35]

Jacques Laurent believes that, over time, compromised vascularization of the horse tongue leads to lingual amyotrophy and impaired epi-critical and deep sensitivity.^[35]

Swedish dressage rider Patrik Kittel is controversial for repeatedly riding a horse whose tongue has turned blue: Akeem Foldager in 2014^[36][37][38] and Watermill Scandic in 2009^[38] (a scandal for which he was cleared by the International Federation for Equestrian Sports^[39]), then again in 2014.^[40]

Of the 261 trotters examined by Tuomola and colleagues in 2019, nine horses had tongue lesions, four had bitten their tongues during the race (1.5%), three had bruises under the tongue (1.1%), and two had bruises on the sides of the tongue (0.8%).^[41] However, it is unclear whether these lingual lesions are always caused by the bit.^[42]

When oral bleeding is visible in a horse, it is often suggested that this is due to the horse biting its tongue.^[3] However, this explanation is not consistent with the results of the study, as only one of the four tongue-biting horses bled.^[3] The explanation for oral bleeding is more likely to be found in other pre-existing lesions during harness racing.^[3]

In principle, the abundant blood supply and moist environment of the horse's mouth promote wound healing.^[3] The time required to replace all epithelial cells has been estimated at 52–75 days for the skin, 41–57 days for the gums and 25 days for the oral mucosa.^[3]

However, the persistence of an inflammatory response delays the healing of oral lesions, as does the presence of foreign bodies in the wound, a cause of intense inflammatory reaction that interferes with normal healing.^[3] For Tuomola et al. a bit can be likened to a foreign body in the mouth, potentially preventing wound healing.^[3]

 

In the event of oral pain, the horse sends out behavioral signals.^[3] Signals of bit-related pain overlap those observed in horses ridden in conflict with their rider, suggesting that bit-related oral pain is a major cause.^[43] On the other hand, severe oral pain makes veterinary examination of the horses concerned difficult, as they may strongly avoid being touched in the mouth.^[3]

According to David Mellor and Ngaio Beausoleil, "most horses show clear behavioral signs of aversion to a bit in the mouth, ranging from mild irritation to intense pain".^[44] These signals include the horse's resistance to being bridled and accepting the bit, mouth opening, teeth grinding, very profuse salivation and tongue movements.^[45] The position of the head and neck (movements to escape the bit), a characteristic facial expression (eyes rolled back, dilated nostrils), movements (tail whipping) and a "crabbed" gait of the whole body also help to identify it.^[45] This evidence of aversion is clearly visible when compared to the absence of these behaviors in wild horses and domestic horses ridden without bit or bridle.^[4]

There are also sexist beliefs and stereotypes associated with mares that attribute this type of behavior to their gender, which can compromise the mare's well-being if its behavior is interpreted solely according to these beliefs, or if it is ignored.^[46]

If a horse experiences regular oral pain from biting, it is likely to anticipate this pain by showing anxiety or even fear around it, especially if it is severe.^[47] Mellor identifies breathlessness as a consequence of bit-related mouth pain, particularly during dressage sessions.^[43]

 

Many riders mistakenly believe that horses cannot suffer from bit-related mouth pain.^[48] Many veterinarians consider it likely that pain signals emitted by horses are not recognized by the vast majority of human beings because they are frequently observed, and therefore considered normal, a phenomenon known as bit-blindness.^[49] Tuomola et al. note that racehorse coaches were surprised to learn that their animals had severe lesions.^[3]

Tuomola and colleagues recommend a systematic check of the bit-wearing area in horses by riders, as well as by show organizers.^[22] In their 2019 study of trotters, these researchers note that of the 20% of horses (51/261) with severe lesions (horses with either multiple lesions or large, deep lesions likely to cause considerable pain and heal slowly), 65% (33/51) competed again within 2 weeks of the study, 13 competed within a week, and two competed again the following day.^[50] The lesions most likely did not have time to heal before the next race.^[3]

This team believes it is essential to "minimize these negative experiences by preventing or at least promptly diagnosing and treating injuries and ensuring conditions that avoid suffering",^[51] by carefully assessing when the horse can be considered fit to compete.^[3] Finnish racing guidelines require official racecourse veterinarians to examine horses after a horse racing, but only if they show bleeding from the mouth.^[14]

• Horse welfare
• Bit (horse)
• Bitless bridle
• Crop (implement)

• Björnsdóttir, Sigríður; Frey, Rebecka; Kristjansson, Thorvaldur; Lundström, Torbjörn (2014). "Bit-related lesions in Icelandic competition horses". Acta Veterinaria Scandinavica. 56 (1): 40. doi:10.1186/s13028-014-0040-8. ISSN 1751-0147. PMC 4236600. PMID 25116656.
• Cook, W. (2006). The effect of the bit on the behaviour of the horse. S2CID 196591934.
• Cook, W. R.; Kibler, W. (2019). "Behavioural assessment of pain in 66 horses, with and without a bit". Equine Veterinary Education. 31 (10): 551–560. doi:10.1111/eve.12916. ISSN 0957-7734. Retrieved 18 August 2022.
• Mellor, David J. (2020). "Mouth Pain in Horses: Physiological Foundations, Behavioural Indices, Welfare Implications, and a Suggested Solution". Animals. 10 (4): 572. doi:10.3390/ani10040572. ISSN 2076-2615. PMC 7222381.
• Tell, Anna; Egenvall, Agneta; Lundström, Torbjörn; Wattle, Ove (2008). "The prevalence of oral ulceration in Swedish horses when ridden with bit and bridle and when unridden". The Veterinary Journal. 178 (3): 405–410. doi:10.1016/j.tvjl.2008.09.020. ISSN 1090-0233. Retrieved 26 June 2022.
• Tuomola, Kati; Mäki-Kihniä, Nina; Kujala-Wirth, Minna; Mykkänen, Anna (2019). "Oral Lesions in the Bit Area in Finnish Trotters After a Race: Lesion Evaluation, Scoring, and Occurrence". Frontiers in Veterinary Science. 6. doi:10.3389/fvets.2019.00206. ISSN 2297-1769. PMC 6640207.
• Tuomola, Kati; Mäki-Kihniä, Nina; Valros, Anna; Mykkänen, Anna (2021). "Bit-Related Lesions in Event Horses After a Cross-Country Test". Frontiers in Veterinary Science. 8 (2297–1769). Veterinary Science. doi:10.3389/fvets.2021.651160. PMC 8044447. PMID 33869325.
• Henry, Guillaume (2017). L'usage des mains (in French). Humensis. ISBN 978-2-410-01052-7.