Ulcers that affect the lower acid-producing part of the horse’s stomach, known as equine glandular gastric disease, remain a poorly understood disorder, according to a just-published review.
Horses have two distinct stomach regions. The lower portion, the glandular mucosa, consists of glands that secrete hydrochloric acid, pepsinogen, histamine, mucous, and sodium bicarbonate.
The upper part of the stomach, the squamous mucosa, does not have these glands and lacks the acid protections found in the lower portion.
Equine glandular gastric disease (EGGD) refers to ulcers affecting the lower glandular portion of the stomach, while equine squamous gastric disease (ESGD) refers to ulcers of the upper portion.
The umbrella term equine gastric ulcer syndrome (EGUS) refers to disease of any portion of the stomach.
For their review, Heidi Banse and Frank Andrews focused on EGGD, investigating its prevalence, impact and management strategies.
EGGD has been considered by some as an emerging disease in horses, noted the pair, who are with the Equine Health Studies Program within the School of Veterinary Medicine at Louisiana State University in Baton Rouge.
“Prevalence appears to be variable, depending upon breed and discipline,” they wrote in the journal, Veterinary Medicine: Research and Reports.
“Primary identified risk factors include exercise frequency and stress; therefore, management strategies are focused on reducing exercise and stress.
“Limiting grain intake and increasing pasture turnout may also be helpful preventative measures.”
Drug treatment consists primarily of an approved omeprazole product with or without misoprostol or sucralfate. Further research into the disordered physiological processes associated with EGGD may allow for the identification of other targeted treatments, they said.
Factors that have been proposed to contribute to spontaneous EGGD include the breakdown of the mucosal defence, bacterial colonization, stress, and inflammation.
The glandular portion of the stomach is constantly exposed to hydrochloric acid, they noted, and, unlike the upper portion, has several protective factors to prevent damage.
“Therefore, it has been proposed that breakdown of protective factors, rather than exposure to hydrochloric acid alone, may be a key factor in development of EGGD.”
The role of bacteria in formation or persistence in EGGD remains unclear, they said. However, there is presently no evidence that changes in the gastric microbiome or secondary bacterial colonization play a key role in the development or persistence of EGGD.
The researchers noted that, to date, no studies have specifically described clinical signs of EGGD.
“Therefore, clinical signs of EGGD are considered under the umbrella of EGUS and are variable and vague.”
Clinical signs include poor body condition or weight loss, poor performance, behavioral abnormalities (nervousness or aggression), poor appetite or overt signs of mild to moderate intermittent colic.
“Unfortunately, due to the nonspecific clinical signs associated with EGUS, diagnosis based on clinical signs is unreliable.”
An endoscopic examination in order to see the stomach lesions is currently the only way to achieve a definitive diagnosis.
In general, EGGD prevalence appears to be higher among sport horses and warmblood show jumpers, compared to other breeds and disciplines.
“However, variability exists between studies and to date, only one study directly compares multiple breeds.
“Recent data has suggested that increased stress or sensitivity to stress may contribute to the development or persistence of EGGD. The presence of increased cortisol after exercise in both warmbloods and thoroughbreds suggests that exercise can be stressful.”
To date, management and treatment strategies have largely focused on what is known about risk factors for all equine stomach ulcers, occurring both in the upper and lower portions.
“However, this may not be appropriate, since pathophysiology and risk factors for the two diseases likely differ.
“The relationship between the presence or severity of ESGD and presence or severity of EGGD is inconsistent, suggesting that the two types of gastric disease may require different treatment or management strategies.
“Based on identified risk factors, it seems that decreasing exercise duration or frequency may help decrease development of disease. Furthermore, minimizing stress may help decrease EGGD formation.
“However, evaluating what an individual horse finds stressful can be challenging.”
Banse and Andrews note that across the three studies they found that specifically evaluated management factors associated with EGGD, dietary factors were not retained in the final multivariable models, suggesting dietary factors may be less important for control of EGGD when compared to ESGD.
However, modeling in these studies suggested that decreased pasture turnout or increased grain concentrate frequency may be associated with EGGD.
“Therefore, increasing pasture turnout and decreasing grain concentrates might be useful management strategies for preventing EGGD.”
Drug treatments include acid-suppressant therapies, histamine type-2 antagonists, coating agents (sucralfate), and synthetic prostaglandins (misoprostol).
The most common acid-suppressing drug used in horses is omeprazole. Its effectiveness in treating ulcers in the upper part of the stomach is well established. “However, it appears less effective for treatment of EGGD. This may in part be due to the low bioavailability of the oral formulation of omeprazole in horses, feeding practices and timing of dosing and feeding.
“Free choice hay decreases omeprazole absorption and duration of acid suppression.
“A compounded intramuscular formulation has recently been reported to result in improved EGGD healing rates; however, direct comparisons between this product and oral omeprazole have not been performed.
“Unless safety and treatment superiority of the compounded omeprazole can be demonstrated, the FDA-approved oral omeprazole formulations are preferred in the USA.”
They noted that omeprazole plus sucralfate – the latter binding to the ulcer bed, creating a physical barrier that protects the mucosa from acid – has been shown to lead to healing a majority of horses in studies.
“EGGD remains a poorly understood disorder of the equine stomach,” they concluded, urging more research into the condition.
Equine glandular gastric disease: prevalence, impact and management strategies
Heidi E Banse and Frank M Andrews
Veterinary Medicine: Research and Reports 2019:10 69–76 DOI https://doi.org/10.2147/VMRR.S174427