Equine gastric ulcer syndrome

What it is

Equine gastric ulcer syndrome (EGUS) groups the erosive and ulcerative lesions of the horse's stomach. The 2015 consensus of the European College of Equine Internal Medicine (ECEIM) divides it into two diseases, because they affect different mucosae and have different causes and treatments:

• Equine squamous gastric disease (ESGD): lesions of the non-glandular part of the stomach, which has no defences against acid. They occur when acid and volatile fatty acids in the gastric contents bathe that mucosa. It can be primary, in otherwise healthy horses, or secondary to delayed gastric emptying (for example, from pyloric obstruction).
• Equine glandular gastric disease (EGGD): lesions of the glandular mucosa, mainly of the pyloric antrum. They are thought to result from a failure of mucosal protective mechanisms rather than from acid itself, but the cause is not clear.

The horse secretes acid continuously, whether it eats or not. Chewing forage produces saliva rich in bicarbonate, and forage forms a mat that protects the squamous mucosa; this is why long fasts, starch-rich rations low in forage, and exercise, which raises abdominal pressure and pushes acid up into the squamous region, favour ESGD.

Who it affects

Horses of every type, but especially performance horses. According to the ECEIM consensus, ESGD affects 37% of untrained Thoroughbreds and reaches 80–100% within 2–3 months of race training; it is also common in Standardbreds and in endurance, sport and leisure horses. Risk factors for ESGD are intense exercise, long intervals without forage, high-starch rations, straw as the only forage and no water at pasture. Those for EGGD are poorly defined and, according to the consensus, there is little evidence that diet influences it.

Anatomy involved

• Stomach (Ventriculus): small for the size of the horse, it lies in the left, intrathoracic part of the abdomen, protected by the last ribs. Its mucosa has two parts separated by an irregular raised line, the margo plicatus: the squamous (non-glandular) region, with a stratified epithelium like that of the oesophagus, which occupies the saccus caecus and the dorsal part, and the glandular region, which includes the proper gastric glands of the fundus and body, which secrete acid, and the pyloric glands of the antrum. ESGD lesions concentrate along the margo plicatus, especially on the lesser curvature, and EGGD lesions in the pyloric antrum and around the pylorus.
• Oesophagus: enters the stomach at the cardia at a very acute angle and with a strongly developed sphincter, which explains why the horse can hardly vomit. Its squamous mucosa is continuous with that of the stomach. Gastroscopy needs a long endoscope, about 3 m, to pass along the oesophagus and reach the pylorus.

Clinical signs

Many horses with ulcers show no signs. Those described are non-specific: picky or reduced appetite, loss of body condition, mild or recurrent colic, teeth grinding, behavioural changes (irritability, nervousness, discomfort when girthed) and poor performance. None of them allows the disease to be diagnosed on its own.

Diagnosis

• Gastroscopy: the only reliable test. It is performed after withholding solid feed and should examine the squamous region, the margo plicatus, the glandular fundus, the pyloric antrum and the pylorus. ESGD is graded with the Equine Gastric Ulcer Council 0–4 scale, recommended by the consensus; there is no validated scale for EGGD, and describing the location, distribution and appearance of the lesions is recommended.
• Lesion severity does not correlate well with clinical signs, and the lesions found may not be the cause of the horse's problem: other causes of colic or poor performance must be ruled out.
• No blood or faecal test has enough diagnostic value.

Treatment and prevention

• ESGD: oral omeprazole, a proton pump inhibitor, for about 4 weeks heals most squamous lesions. The consensus recommends 4 mg/kg daily of the buffered formulations; enteric-coated granule formulations have worked well at lower doses. Long-acting injectable formulations exist.
• EGGD: responds much less well to omeprazole alone. The 2015 consensus recommended adding sucralfate; later studies have shown better results with misoprostol, a prostaglandin E1 analogue, which should be handled with gloves and must not be handled by pregnant women because of its abortifacient effect.
• Gastroscopy is repeated to confirm healing before stopping treatment.
• Prevention and management: forage available almost continuously, without gaps of more than 6 hours; no more than 2 g of starch per kg of body weight per day or 1 g/kg per meal; alfalfa hay for working horses; some forage before exercise; turnout; and water always available. In risk periods (competitions, travel, changes of yard) low-dose preventive omeprazole can be used.
• The horse is a food-producing species in many countries. In the EU its passport states whether it is excluded from the food chain, and this determines which medicines may be used and with which withdrawal periods; several of these drugs are not authorised for equids.

Key studies

• ECEIM consensus (Sykes et al., 2015): separated ESGD and EGGD, recommended the 0–4 scale for ESGD and advised against grading EGGD until a validated scale exists. It reports ESGD prevalences of 80–100% in Thoroughbreds in training and healing rates of 70–77% with buffered omeprazole at 4 mg/kg for 28 days, and for EGGD it recommended omeprazole plus sucralfate (12 mg/kg every 12 hours). It is expert opinion based on studies of variable quality.
• Sykes et al. (2015), randomised blinded trial in 60 Thoroughbred racehorses with grade ≥ 2 ulcers given 1, 2 or 4 mg/kg of enteric-coated omeprazole before exercise. The lower doses were non-inferior to 4 mg/kg for ESGD. At 28 days, 86% of squamous lesions had healed versus 14% of glandular lesions, and EGGD worsened in 36% of horses. Horses received the drug after a brief fast, which may favour its efficacy.
• Mason et al. (2019), meta-analysis of 7 randomised trials with 566 horses in training. Preventive omeprazole reduced the occurrence of ulcers compared with sham (RR 0.28; 95% CI 0.18–0.43): 23.4% of treated horses developed them versus 77.2% of controls. Preventive doses varied between trials, and the data come from racehorses and mostly from squamous lesions.
• Varley et al. (2019), prospective study in 63 sport horses with grade > 1 EGGD. Misoprostol (5 µg/kg every 12 hours) healed 72% of cases versus 20% with omeprazole plus sucralfate, and healing was associated with resolution of signs (OR 11). Treatment was allocated by centre, not at random, and owners were not blinded.
• Luthersson et al. (2009), cross-sectional study of 201 non-racing horses from 23 yards in Denmark. 53% had grade ≥ 2 ulcers. Straw as the only forage, more than 2 g/kg of starch per day or more than 1 g/kg per meal, and no water at pasture were associated with higher risk; for ESGD, so were more than 6 hours between forage meals. It was carried out only in winter, with horses stabled.