Ill-fitting bits found to be common in assessed horses in study

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Bit thickness fit: The image shows a bit that fits, providing the tongue with enough space. Photo: Anttila et al. https://doi.org/10.3389/fvets.2022.879048
Bit thickness fit: The image shows a bit that fits, providing the tongue with enough space. Photo: Anttila et al. https://doi.org/10.3389/fvets.2022.879048

The use of poorly fitting bits was common in a study involving 554 horses in Finland, researchers report.

A bit that fits is essential for horse welfare and good communication with the animal, University of Helsinki researchers said.

Bits place pressure on the sensitive structures of the horse’s mouth.

Mirjami Anttila, Marja Raekallio and Anna Valros investigated variations in the oral dimensions of adult horses and ponies of various breeds in the areas related to bit fit.

They then evaluated bit fit by comparing the oral dimensions with the currently used bit provided by the horse owner, who was invited to bring it along.

The study population consisted of 308 geldings and 246 mares, aged 5 to 29, put forward for routine dental care. About half were used competitively, while 218 were classified as pleasure horses for riding or driving. Another 62 were used for harness racing.

All horses were examined by Anttila, a veterinarian experienced in equine dentistry. The mouth width, distance between upper and lower jaw, tongue thickness and lower jaw width, were measured under sedation.

A bit that is too thick, with too little space left for the tongue. The tongue is retracted partly behind the bit. Photo: Anttila et al. https://doi.org/10.3389/fvets.2022.879048
A bit that is too thick, with too little space left for the tongue. The tongue is retracted partly behind the bit. Photo: Anttila et al. https://doi.org/10.3389/fvets.2022.879048

All oral dimensions varied by breed and sex, they said. Mouth width and the gap between upper and lower jaw were affected by age. Oral dimensions were significantly smaller in mares than in geldings.

In coldblood Finnhorses, oral dimensions were greater than in other breeds; in ponies they were smaller.

Bit details were recorded for 465 of the 554 horses, with five of them (1.1%) being ridden bitless.

“It was common to use a bit that did not fit the horse,” the study team wrote in the journal Frontiers in Veterinary Science.

“The bit was either too short or too long (over 10mm longer) compared to mouth width, compressed the tongue in between the upper and lower jaw, or the center link was of similar length compared to lower jaw width, thus possibly causing pressure points or a nutcracker effect on the bars of the lower jaw.”

Oral dimension measurements: (A) mouth width, (B) distance between upper and lower jaw, (C) tongue thickness, (D) lower jaw width. Photo: Anttila et al. https://doi.org/10.3389/fvets.2022.879048
Oral dimension measurements: (A) mouth width, (B) distance between upper and lower jaw, (C) tongue thickness, (D) lower jaw width. Photo: Anttila et al. https://doi.org/10.3389/fvets.2022.879048

Horses and ponies had, on average, a bit that was 3.6mm longer than mouth width, but the bits ranged from being 20mm shorter to 30mm longer.

Bit length was assessed as a fit in 313 of 422 horses in which bits were evaluated, representing 74.2%. However, 109 of the horses – just over a quarter of the 422 horses – had a bit length that did not fit. Being too short was a little more common than being too long.

The space available for the bit between the jaws in the study horses ranged from 5mm to 22 mm, with the average being 14mm. Assessment of bit thickness showed that, on average, horses had 0.3mm of spare space left between the upper and lower jaw when the bit was in the mouth and tongue thickness was taken into account.

Horses had, on average, space for a 14mm thick bit without compressing the tongue, they reported.

In some cases, the researchers found the bit was too thick and compressed the tongue.

The most used mouthpiece was a double-jointed snaffle (46.0%), followed by a single-jointed snaffle (30.5%), a straight solid or flexible bit (11.6%), a barrel bit (6.5%) and a straight ported bit (1.9%). Another 2.4% were classified as “other”.

The most common bit cheek type was a loose O-ring, used by two-thirds of the riders. Other bit cheek types were fixed ring (25.6%), vertical shank (4.8%), horizontal shank (2.4%) and Baucher (1.1%).

The most common bit material was stainless steel, used in 74.0% of cases. Metal alloys or combinations of metals were used in 15% of the bits presented by owners.

Discussing their findings, the authors noted that the largest variation in oral dimensions was found between horse breeds.

“This supports previous findings that the largest variation in the skull dimensions between breeds is found in the nasal part of the skull.”

All oral dimensions of geldings were greater than those of mares, which may be explained by the effect of sex hormones on horse growth.

“Although breed, age and sex explain part of the variation in the oral dimensions of adult horses and ponies, individual differences exist, which enhances the importance of measuring oral dimensions and evaluating bit fit regularly as the horse ages.”

The study team recommended that the fit of the bit is evaluated regularly as horses age.

Anttila M, Raekallio M and Valros A (2022) Oral Dimensions Related to Bit Size in Adult Horses and Ponies. Front. Vet. Sci. 9:879048. doi: 10.3389/fvets.2022.879048

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

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