New Developments In GI Issues In Horses

Horse owners continue to deal with Equine gastrointestinal problems.


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Photos courtesy of Freedom Health LLC

Equine gastrointestinal problems remain ongoing issues for horse owners, and researchers are working to find new ways to allay these problems. Helping owners treat horses kept in 21st century conditions are at the top of the list.  New tests can now find causative agents for diarrhea in both young and adult horses. 

Gastric, Colonic Ulcers

Researchers are trying to solve the ongoing problem of management for the modern horse. Pastures are rarer than ever before, horses are stalled a good deal of the time, and equine athletes require more energy than hay alone can give.

It’s long been understood that these management methods have created problems in the horse, in particular in gastric and colonic ulcers. Since it would be difficult if not impossible for many horsemen to change, researchers are trying to find ways to work around these issues.

Cherry Ulcer

Omeprazole has been recognized for many years as an important medication in healing gastric ulcers. GastroGard is the FDA-approved prescription version for treatment while UlcerGard is the FDA-approved preventive medication to use during times of stress and increased gastric ulcer risk, such as when competing. Both are products of Merial Ltd. of Duluth, Ga.

Hoyt Cheramie, DVM, MS, Dipl. ACVS, manager of Large Animal Veterinary Services at Merial, says it’s also important to take feeding into consideration when treating and preventing ulcers.

Feeding hay free-choice to duplicate grazing has been one of the methods touted, but Dr. Cheramie says this can be counterproductive.

Gastic Ulcer

“People often feed hay free-choice, but because there is little moisture in hay the horse can pack quite a bit of dry roughage into the stomach in a short period of time, and then some horses may not eat again for a while,” he says.

“As horses are continuous grazers, this may have a negative effect on overall saliva production. Adequate bicarbonate-rich saliva is needed to buffer the acid to correct pH levels to prevent gastric mucosal damage while promoting pepsinogen conversion to pepsin—the primary role of acid in equine digestion.

“Despite the roughage present, the stomach becomes more acidic over time because of the decrease in saliva production and continuous acid production. Now the acid builds to a high level, and the pH drops to potentially damaging levels or levels not promotive of mucosal healing.”

Three types of salamander larvae

Right Dorsal Colitis

Cheramie says that constant grazing is important and recommends using roughage-restricting feeder devices, such as specially designed hay bags and paddock feeders, when horses don’t have access to grazing.  These devices force the horse to “graze” the same amount of hay over longer time periods, increasing saliva production throughout the day. Added benefits include decreased hay wastage and improved diet management in overweight horses.

Colonic ulcers are also a problem in domestic horses. Although the etiology of colonic ulceration is not yet understood, a peer-reviewed study verifies their existence. Symptoms of colonic ulcers include girthiness, flank sensitivity (especially on the right side), tucked-up abdomen, diarrhea, poor hair coat and eye, and difficulty bending and collecting.

In 2003, Franklin L. Pellegrini, DVM, conducted necropies on 180 performance horses in a Texas slaughterhouse. The results, published in 2005 in the Journal of Equine Veterinary Science, revealed that 87 percent had gastric ulcers and 63 percent had colonic ulcers. As a result of this and three separate unpublished studies over six years, Pellegrini believes colonic ulceration may stem from the action of pathogenic bacteria on the exposed, compromised mucosal lining, which results in endotoxins or exotoxins entering the bloodstream.

To treat the ulcers, Peter M.J. Bedding, PhD, devised a once-a-day digestive conditioning supplement called Succeed by Freedom Health LLC of Aurora, Ohio. It normalizes the GI tract of the horse without requiring a diet change. Succeed increases nutritional uptake so the amount of hard feed can be reduced, and slows down the passage of grain and rebalances the bacteria in the foregut and hindgut. Ingredients of the U.S.-patented formula include polar lipids, betaglucan, glutamine, threonine, nucleotides and mannan oligosaccharides.

“It’s important to differentiate gastric from colonic ulcers because the treatment protocols are absolutely different,” says Dr. Pellegrini, now vice president of veterinary medicine for Freedom Health.

“If you go with the standardized FDA-approved gastric ulcer treatment, you could exacerbate the colonic ulceration, particularly if the horse is fed concentrates,” Pellegrinit notes. To aid the diagnosis, Freedom Health devised an antibody test that can indicate whether the horse has a foregut or a hindgut issue. The company will release an improved version of the Succeed Equine Fecal Blood Test later in the year.

Causes of Diarrhea

Nathan M. Slovis, DVM, Dipl. ACVIM, CHT, of Hagyard Equine Medical Institute at the McGee Medical Center in Lexington, Ky., has been working to find the causative agents for diarrhea in horses. He concluded that the conventional lab test wasn’t often able to find a diagnosis.
Three years ago, he began collaborating with Idexx Reference Laboratories’ Christian Leutenegger, DVM, PhD, FVH, director of the company’s Molecular Diagnostics Laboratory.

Dr. Leutenegger has a bacteria bank at his disposal and was able to get the genetic code for several bacteria that cause diseases in horses as well as in humans and small animals. The idea was to see if there were any untested bacteria that were prevalent in horses.

“We looked at a variety of different organisms,” says Dr. Slovis. “We wanted an all-inclusive test that only required a gram of feces, about the size of a quarter.”

The test, called the Idexx Equine Diarrhea RealPCR Panel, was a success, and gives 10 results with one sample: rotavirus, equine coronavirus, Clostridium difficile toxin A, Clostridium difficile toxin B, Neorickettsia risticii, Clostridium perfringens enterotoxin A, Lawsonia intracellularis, Rhodococcus equi, Cryptosporidium spp. and Salmonella spp. The panel doesn’t report the sensitivity pattern of the bacteria to antibiotics. It’s an adjunctive test.

“The results from the PCR panel come back quickly, whereas a culture can take three to five days,” Slovis says.  “With the PCR panel results you can get started on the treatment while you wait to get your culture back.”

In the past year, the PCR panel has also identified an equine rotavirus strain that is different from the conventional equine strain, which is similar to the human strain. Human tests are usually used to check for rotavirus, but in one particular case the test was negative.

“When we used the PCR panel, it was positive,” Slovis says. “We isolated an equine strain and DNA tested it and discovered that it wasn’t that similar to the human strain. It didn’t affect the treatment but at least the owners knew, and the big question is, will the vaccines that currently protect against rotavirus protect against this equine-specific strain? Can you get cross productivity?” Slovis plans to publish a paper on this subject later this year.

The PCR panel also identified a strain of coronavirus that affects adult horses.

“We sent off the manure to the University of Kentucky Gluck Center and Udeni Balasuriya, and he isolated the virus,” Slovis says. “France is sending over a veterinarian to work with him and learn more about this coronavirus, because not much is known about it in horses. The plan is to do experiments to find out how easily it affects a healthy adult horse.” 

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