Today, we know horses are prone to developing gastric (or stomach) ulcers. We know an estimated 50-90% of horses suffer from gastric ulcers and that performance and racehorses are some of the most susceptible. We even know what treatment and management options can help ulcers heal and reduce their changes of returning.

But concern about gastric ulcers weren’t always common. In fact, not long ago, relatively speaking, veterinarians published some of the first research on these stomach lesions. Al Merritt, DVM, Dipl. ACVIM, a professor emeritus at the University of Florida College of Veterinary Medicine, in Gainesville, described what researchers have learned about equine gastric ulcers in the past three decades at the 2018 Kentucky Equine Research Conference, held Oct. 29-30 in Lexington, Kentucky.

Gastric Anatomy and Physiology

Merritt began with a brief review of the equine stomach—an important part of fully understanding gastric ulcers.

The horse’s stomach has two regions: a nonglandular (squamous mucosa) portion comprising the upper third and a glandular lower portion. The squamous nonglandular region doesn’t have the same protective mucus and bicarbonate (a pH buffer) layer that the glandular region does, leaving it vulnerable to ulceration from gastric acid. The demarcation line between the two portions is called the margo plicatus.

Using a herd of cannulated horses (meaning they had tubes placed through their sides and into their stomachs so researchers could study the contents) established at UF in 1985, Merritt and colleagues confirmed that the glandular portion is very acidic, with a pH of 1 to 2, while the nonglandular region has a fairly neutral pH of 5 to 7.

Horses produce gastric acid continuously, whether they’re eating or not. When they chew, their bodies release saliva, which contains sodium bicarbonate and calcium—both of which act to buffer stomach acid. This is all well and good if horses are grazing continuously, as they evolved to, but human management can put a wrench in the gears.

When we supply horses with a few meals each day, the stomach keeps producing acid, but there’s not a steady saliva supply. This leaves the stomach environment to become increasingly acidic and raises ulcer risk.

A First Look at Stomach Ulcers

Gastric ulcers are one of the most common concerns among horse owners and veterinarians today, but they weren’t always at the top of vets’ differential diagnoses when health problems arose.

“What really got us excited about ulcers in horses was a paper that came out in 1986,” Merritt said.

Researchers evaluated necropsy findings from retired Thoroughbreds in Hong Kong, where they identified gastric lesions confined to the squamous mucosa, but with no accompanying duodenal lesions (these were common in foals with a condition called gastroduodenal ulcer disease, which was prevalent in the mid-1980s). They also found that, in several horses, lesions were localized to the margo plicatus.

Not long after, endoscopes (long, flexible tubes with cameras attached) made their entrance into the equine veterinary community. Today, veterinarians use endoscopes to conduct gastroscopy—during which a veterinarian passes the tool through the horse’s nostril, down the esophagus, and into the stomach to see inside it—which is the only definitive way to diagnose gastric ulcers

One prototype—the Olympus—debuted in 1985, Merritt said. It was about 2.7 meters long and, while it wasn’t readily available for practitioners, it did provide “some pretty good images, and we could see evidence of squamous ulceration,” he said.

Eventually, more endoscopes hit the market and became increasingly common, and scientists developed videoendoscopes, which provided more dynamic views of the stomach. Several researchers began conducting endoscopy studies in horses, and Merial published gastroscopy guidelines in 2001, Merritt said.

Veterinarians eventually realized gastric ulcers were significant problems for high-performance horses, and researchers began studying them more regularly. In 1999, the Equine Gastric Ulcer Council published its recommendations for diagnosing and treating equine gastric ulcer syndrome (EGUS), the first introduction of the term that’s well-known today.

At the time, the council said common compatible clinical signs included:

• Poor appetite;
• Dullness;
• Attitude changes;
• Decreased performance;
• Poor body condition; and
• Low-grade colic.

While these signs still point to ulcers, Merritt noted that “we know now that they don’t even have to show signs to have gastric ulcers.”

The council also stated that endoscopy is the only way to definitively diagnose ulcers, which still holds true today.

Around that same time, he said, two gastric ulcer scoring systems were introduced, with a five-point system (0 to 4) catching on with most veterinarians and researchers. Both methods, he added, were designed for use in grading squamous lesions.

Newer Research

Since 1999, researchers have made significant improvements in understanding gastric ulcers, how to treat them, and how to reduce the risk of their development, Merritt said.

Some key developments over the years include:

• Scientists learned that gastric ulcers aren’t just a problem for horses in training when they identified lesions in 16 of 17 horses stabled full-time, 125 of 141 horses turned out to pasture for at least four hours each day, and in all 13 horses turned out full-time;
• Eventually, researchers separated EGUS into two categories: equine glandular gastric disease (EGGD) and equine squamous gastric disease (ESGD);
• In an exercise study, scientists found that the pH within the top squamous-lined part of the horse’s stomach dropped below 4 (the “cutoff” for when the pH is corrosive to the squamous lining) when horses began trotting and continued into gallop; it then came back up when the horses moved to a walk;
• In the same exercise study, they determined that intra-abdominal and intragastric pressure increased during exercise, which likely pushes the glandular region’s contents (including gastric acid) up into the unbuffered squamous area;
• Horses were more likely to have both EGGD and ESGD if they ate large amounts of concentrates;
• Scientists identified other potential gastric causes as stress (they suspect these horses might be tenser and tighter, which could push acid farther up into the squamous region) and meal-feeding;
• Researchers found that horses with higher body condition scores also had higher ulcer scores; and
• Risk factors for gastric ulcer development include feeding unprocessed grains, infrequent feeding of a complete and balanced diet, a lack of hay or haylage in the diet, and no grass turnout.

Ulcer Treatment and Management

As they were learning more about ulcers, researchers were also working to find treatment methods that would increase overall gastric pH, buffer the horse’s stomach contents, and/or allow existing ulcers to heal, Merritt said.

In 1987, he said, researchers found that a small dose of intravenous ranitidine reduced stomach acid concentration in fluids but didn’t have much effect on pH. Later they found that a higher 6.6 mg/kg dose given orally helped keep horses’ gastric pH above 4, but it was only effective if owners or veterinarians administered it three times daily.

“Three times a day isn’t really practical,” Merritt said, so researchers kept looking for other options.

In 1992, he and colleagues tested enteric coated omeprazole granules with good results and, subsequently, helped Merial develop an oral paste formulation. They tested the product in a field trial in 1999, showing that it was effective in treating ESGD. That product eventually went on to become GastroGard, Merritt said. Another product, UlcerGard, is labeled to prevent ulcers from developing.

GastroGard (which is still considered the gold-standard ulcer treatment) and UlcerGard are the only two U.S. Food and Drug Administration-approved products to treat and prevent, respectively, gastric ulcers in horses.

Merritt said researchers are currently studying a longer-acting intramuscular omeprazole and other oral formulations as treatment options.

Veterinarians and nutritionists have also arrived at some feeding strategies to help reduce a horse’s risk for developing ulcers, including:

• Feeding less grain; if horses need extra calories to maintain weight, try adding oil or another fat source to the diet;
• Providing free-choice forage (hay, pasture, or an alternative forage such as hay pellets or cubes);
• Prolonging hay ingestion time by using slow-feeders and/or haynets;
• Adding alfalfa to the diet, which has been shown to aid in gastric buffering; and
• Looking into nutraceuticals; Merritt encouraged owners to look for products with scientific evidence of efficacy.

Moving Forward

Despite all the advancements, researchers are still working to better understand ulcers, particularly EGGD, where, Merritt said, other current research directions include:

• Investigating another drug, sucralfate, which might help coat lesions to allow better healing;
• Finding ways to increase PGE2 (a chemical the body produces that’s involved in inflammation and pain perception) production, which subsequently decreases acid secretion; possible methods include sucralfate or corn oil administration; or treatment with the drug misoprostol. Additional research on these treatments’ efficacy in horses is needed, he said;
• Taking biopsies from lesions to see if yet-unidentified infectious agents are present;
• Identifying specific etiologies (causes) for different types of ulcers; and
• Better characterizing how dietary factors contribute to ulcer development.

The Bottom Line

In the past 30 years, researchers have made great strides in understanding gastric ulcers. Those findings and ones yet to be made can help improve horse health and welfare now and into the future.

“I think it’s safe to say that mild ESGD, small areas of superficial erosions near the margo plicatus, probably falls within the realm of normality for all equids, because that squamous region lies closest to gastric contents that are usually <pH 4.0, which is generally considered the corrosive cutoff,” Merritt said. “The more severe ESGD lesions, those that extend well up into the squamous region and may bleed, and most likely all EGGD lesions, are more likely due to human-determined conditions, such as forced exercise, feeding strategies, housing conditions, increased exposure to infectious agents, and undoubtedly other factors we have not yet thought of.

“Man and horse have a long history of close interaction, which, save for some future unimaginable situation, ‘ain’t gonna change,’” he continued. “But hopefully future management modifications away from dependence on pharmaceuticals that do not impact the quality and expectations of that interaction can be devised that result in a significant reduction in the incidence of all forms of EGUS, for the sake of both man and beast.”

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Erica Larson, News Editor

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

A new horse arrives at the 20-stall boarding facility where your horse resides. He gets turned out in a field with three other horses, and all seems well. But after about a week, he starts to develop an abscess beneath his jaw, and a couple of the horses he’s pastured with are coughing.

Does the horse have strangles? Is the rest of the barn at risk?

This is a panic-inducing scenario many veterinarians might encounter on clients’ properties. So David Rendle, BVCs, MVM, CertEM(IntMed), Dipl. ECEIM, MRCVS, of Rainbow Equine Hospital, in North Yorkshire, U.K., described how to handle it while at the 2018 British Equine Veterinary Association Congress, held Sept. 12-15, in Birmingham.

Strangles develops when Streptococcus equi bacteria infect horses’ head and neck lymph nodes, sometimes resulting in painful abscesses. It’s highly contagious and can spread rapidly through horse populations and barns.

Clinical Signs

When evaluating a suspected strangles case, said Rendle, the veterinarian should first gather the horse’s history and a timeline of his clinical signs. This might include asking questions such as, how old is the horse (younger horses are more likely to be affected by S. equi)? What signs has he shown over the past two weeks? Does he have a history of dental or respiratory disease (which can be confused for strangles)?

Typical clinical signs of strangles include lethargy, fever, cough, and that telltale abscess. The first signs you’ll see, usually within three to 14 days of exposure, said Rendle, are lethargy and fever.

“Fever occurs before horses become contagious, providing an opportunity to isolate and halt the spread of infection,” he said.

About two to three days after the horse develops a fever, he typically starts shedding the bacterium via pus-filled nasal discharge. Nasal shedding can last for two to three weeks or longer if infection sets up within the sinuses or guttural pouches (cavities in the back of the head), he said. Not until one to four weeks later will an abscess develop and burst.

Rendle said infected horses might also show less-obvious signs, including mild transient fever, mild clear discharge, and lack of appetite yet never develop abscesses. “Often these horses are the ones that spread the most disease,” he said. “Transmission from outwardly healthy horses is often more of a problem than transmission from horses with clinical signs.”

Diagnosis

A veterinarian’s ability to confirm a strangles diagnosis depends the stage of disease, which isn’t always known. Rendle recommended performing a guttural pouch lavage (flush) with culture and PCR testing rather than taking less-reliable nasopharyngeal swabs for chronic cases. For more acute cases, he said, timing is critical.

“S. equi doesn’t reside in the nasal passages, so you’re reliant on timing and luck (with swabs),” he said. “It’s only really effective (as a diagnostic) in early infection with copious discharge.”

At least three weeks after all clinical signs have ceased, he suggests performing blood testing on all horses on the property to determine whether they’re carriers. “Ten percent of horses in an outbreak are expected to develop persistent guttural pouch infection,” he said. These horses show no clinical signs yet continue to spread S. equi.

Preventing Disease Spread

If diagnostics do confirm a strangles case, Rendle said property managers should isolate all horses with fever or other clinical signs immediately. These horses should stay in isolation for at least two weeks after clinical signs cease and should undergo testing to confirm they are not carriers before returning to the herd. Rendle said testing typically comprises a blood test to determine which horses have been exposed to strangles, followed by examination of horses with positive blood tests via endoscopy and a guttural pouch wash to check for any remaining bacteria.

If possible, he suggested separating horses into three groups based on what he calls the traffic light system:

• A green group, which has no known contact with the affected horse;
• A yellow group, comprised of horses that had direct or indirect contact with an infected horse; and
• A red group whose signs and test results confirm they have strangles.

House these groups either in three separate buildings or three separate double-fenced paddocks, if possible. Also dedicate equipment and staff to each individual group. If manpower is an issue, then have caretakers move from low- to high-risk groups when feeding and performing chores, said Rendle. While it might not be a popular decision, he added, stop equine movement on and off the property for about four weeks after all horses are declared negative to prevent spread to other properties.

“Take rectal temperatures in all green and yellow horses twice daily,” said Rendle. “And move any pyrexic (feverish) horses or horses with clinical signs to the red group.”

Take-Home Message

Always quarantine new arrivals, particularly at barns with large populations of horses, for at least two weeks, Rendle suggested. And if a strangles case does pop up on your property, practice smart biosecurity, and remember that signs can take a while to appear as well as clear.

“Strangles cannot survive outside the horse, so if carriers were all identified, the disease could be eliminated,” he said. “It remains a problem because horse owners fail to implement appropriate disease control measures.”