Bits and Breathing: What's the Relationship?
By and large, owners and riders take steps to ensure their horses are always able to perform at their best. But is something as simple as putting a bridle on undoing all your hard work and actually hampering your horse’s performance? It’s possible.

Researchers in New Zealand say the tack we use and the way we ride could affect not only a horse’s capacity for breathing but also his feelings of breathlessness. And this could compromise his health, performance, and welfare.

Mouth-gaping caused by bit pain could put the horse’s mouth, tongue, and throat in positions that make it difficult for him to breathe, said David J. Mellor, BSc (Hons), PhD, HonAssocRCVS, ONZM, professor of animal welfare science and foundation director of the Animal Welfare Science and Bioethics Centre at Massey University, in Palmerston, New Zealand.

“The horse is an ‘obligate nasal breather,’ ” meaning they can only breathe through their noses, not their mouths, Mellor said. “So any factors that interfere with that, especially when breathing is near maximum levels during vigorous exercise, will impair athletic performance.

“The closed mouth of the horse that is bit-free has the benefit that the horse, by swallowing, can create and maintain negative pressure in the back of its mouth (in its oropharynx) that holds the soft palate down onto the root of the tongue. This prevents it from ballooning up into the area of the respiratory tract above the soft palate (the nasopharynx), which at least partly obstructs airflow during breathing in and out.”

Removing the bit could “open passageways,” so to speak, to more comfortable breathing for the ridden horse, he said.

“With a bitted bridle, the averseness of the bit often means that the mouth is open, even a small amount, so that the negative pressure cannot be maintained, and the soft palate can then balloon and obstruct the airway above it,” he said. “There are a number of other conditions which may arise independently of the presence of a bit, but the impact of the bit just described can make their obstructive effects on airflow worse.”

Mellor and fellow researcher Ngaio J. Beausoleil, BSc Biology, PGCertSci (Physiology), PhD, deputy directors of the Animal Welfare Science and Bioethics Centre at Massey University, outlined the physiological and biomechanical details of equine breathing in their recent review on the topic. They also described a horse’s likelihood of experiencing three unpleasant sensations of breathlessness as recognized in humans:

  • Unpleasant respiratory effort—The respiratory muscles work harder to try to meet demands in compromised conditions (obstruction);
  • Air hunger—The suffocating feeling felt after holding breath for a long time, for example; and
  • Chest tightness—Airway constriction leading to a feeling of tight pressure in the lungs (such as in equine asthma patients).

Any or all of these feelings could occur when the need to breathe surpasses the body’s ability to respond to that need, they said.

A rider’s bridle use could significantly affect this equilibrium of demand and response, they said. For example, riding on a tight rein “cramps” the head and neck position, Mellor said.

“Low jowl angles (the head flexed low) obstruct the upper respiratory tract, and this often leads to compromised breathing,” Mellor said.

This effect might be intensified by bit use (as opposed to using a bitless bridle), although research has yet to be conducted on this theory, he added.

The reason is not obstruction from the metal piece directly, he said. Rather, it would come from obstruction caused by the horse’s reaction to the bit. Gaping his mouth open to escape bit pressure and rolling his tongue to push against the bit often impedes breathing, making it more difficult and unpleasant, he said.

While the industry already acknowledges performance issues related to labored breathing, it doesn’t necessarily take into account the welfare implications, said Mellor.

“Many breathing problems that lead to ‘exercise intolerance’ in elite equine athletes are well-known and are given serious attention because the horses do not perform as well as they otherwise would,” he told The Horse. “This attention includes changing bitted bridle design and other ‘tack’ applied to horses, including for example tongue ties, bits designed to prevent tongue rolling, retraction and protrusion, and crossed nosebands to minimize mouth opening. Also, veterinary surgical procedures are applied to the structures of the upper respiratory tract in attempts to stop them from partially obstructing the air passages and impeding airflow.”

What would be most useful, however, is more research, he said. While their team has not currently planned for studies in this field, Mellor and Beausoleil said they hope their detailed evaluation will lead to concrete scientific data.

“We are strongly encouraging others to explore a number of the points we have raised in our review, which appears to be exciting significant interest as judged by the number of downloads of the paper from the open-access website,” Mellor said.

The study, “Equine Welfare during Exercise: An Evaluation of Breathing, Breathlessness and Bridles,” was published in Animals.