Periodontal Disease in Horses Linked to Gram-Negative Bacteria, Not Just Food Impaction, in Scottish Study

Equine dentistry is big business these days. The availability of precision power tools for dentistry has given veterinarians and equine dentists an upgrade to first class in the ability to identify problems that could adversely affect the teeth and a horse’s all-important ability to graze and chew its food.

It may be easier to see what’s wrong, and a power tool may be easier to wield than a tooth rasp, but it’s interesting to note that there are still big gaps in the scientific knowledge of the healthy equine mouth, as well as any abnormal conditions or diseases. Dr. Hilary Clayton’s research at the Michigan State University College of Veterinary Medicine’s McPhail Equine Performance Center is an example: she used video fluoroscopy to document how horses used different bits, where bits sit in the mouth and how horses swallowed with different bits. No one had ever documented that before. She asked us to consider what she called “oral conformation”–not all horses’ mouths were shaped the same, she warned, and not all horses would have similar responses to the same bit.

(Note: Dr. Clayton’s studies and comments on bits and the horse’s mouth can be found on the McPhail Equine Performance Center index of dressage-related research published in USDF Connection.)

Likewise, who really knows what happens when horses have dental problems and why one horse suffers when another merely needs occasional floating? Alistair Cox at the University of Edinburgh has completed the first study to describe the very basic microscopic anatomy of equine periodontal disease and the potential role of bacteria; his research was funded by The Horse Trust.

Equine periodontal disease is a common condition in horses. According to a 1970 study by Baker and published in the Equine Veterinary Journal, it affects around 60 percent of British horses over the age of 15 years. The disease is painful and can have a big impact on a horse’s quality of life, affect the animal’s ability to eat and affects its performance.

Although bacteria are known to be a cause of periodontal disease in humans, cats and dogs, their significance in relation to the disease in horses is less clear. Mechanical factors, such as food being packed between the horse’s teeth due to abnormal growth and spaces, were considered to be the primary cause of the problem in horses.

For the research, Cox examined the skulls of 22 horses that had been submitted for post mortem examination. Although none of the horses had received treatment for periodontal disease, 16 had some form of periodontal disease.

“This research, funded by The Horse Trust, highlights how common periodontal disease is in horses. Yet many horses don’t receive treatment so are likely to be suffering in silence. I would advise all horse owners to get their vet or equine dentist to regularly check their horse to see if it is developing the condition,” said Cox.

Cox identified bacteria, including spirochetes, that were associated with the presence of periodontal disease. Spirochetes are known to be important in human and canine periodontal disease, but this is the first study to identify spirochetes associated with equine periodontal disease.

Spirochetes are a type of anerobic, Gram-negative bacteria, so called because they have a spiral shape. They are implicated in several important disease processes.

“This study shows that bacteria may be more important than was previously thought in the development of equine periodontal disease. More research is needed to understand whether bacteria or mechanical factors are the main cause of the disease. Once we have a better understanding of why and how the disease develops, we can do more to prevent horses from developing this painful condition,” said Cox.

The Horse Trust-funded research also found a significant association between the age of the horse and periodontal disease. Skulls were examined from horses ranging from 4 to over 20 years of age. The older horses were found to be more likely to have periodontal disease and a more advanced form of the condition.

Cox examined the skulls under the microscope and under x-ray. He found various histological features associated with equine periodontal disease, including hyperplasia, ulceration and neutrophilic inflammation of the gingival epithelium, mononuclear and eosinophilic inflammation of the gingival lamina propria, and mononuclear inflammation of the periodontal ligament.

Cox also found an association between equine periodontal disease and radiographic evidence of interdental bone lysis and diastemata, but this association was not statistically significant.

Read about the Horse Trust’s previous research on equine oral health on The Jurga Report.

Photos: Pony with charming underbite by Tim Zim; Inside of horse’s mouth by Nancy Sims;? John C. Froenig DVM of the Animal Medical Center in Hutchinson, MN working on mare with a motorized equine dental tool by Peter J. Markham, Loretto, MN. All hosted via

Go to the main page of The Jurga Report to view more content.




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