Dr. Tania Sundra

23 January 2023

Updates in Equine Gastric Disease

by Dr Tania Sundra BSc(Hons) BVMS MANZCVS (Equine Medicine)
Avon Ridge Equine Veterinary Services, Brigadoon, WA, Australia

INTRODUCTION

The term equine gastric ulcer syndrome (EGUS) was previously used to describe squamous gastric disease and glandular gastric disease1. More recently however, there has been a growing appreciation of the differences between both these diseases with a realisation that the pathophysiology, risk factors, treatment and management of squamous disease cannot be extrapolated to glandular disease. Whilst both conditions may occur concurrently, it does not necessarily mean there is an association between them.

Acid suppressive therapy using proton-pump inhibitors remains the cornerstone of treatment for both diseases. Oral omeprazole is the only proton-pump inhibitor registered for the treatment of squamous disease, however, it is no longer considered effective for the treatment of glandular disease 2,3. Following recent trends in human medicine, other alternatives are being explored for both the management of glandular disease, and to improve healing rates for squamous disease. However, implementing management changes to reduce risk factors should be initiated alongside drugs to help improve healing rates and to prevent recurrence of disease when treatment is completed. 

EQUINE SQUAMOUS GASTRIC DISEASE

RISK FACTORS AND MANAGEMENT

Squamous gastric disease primarily occurs as a result of acid injury to a tissue that has limited defence against a low pH environment. Any disruption to the normal stratification of gastric pH will therefore increase the risk of squamous disease. Excessive exposure to acid causes the stratified squamous epithelium to become thickened and hyperkeratotic. Continued acid exposure leads to sloughing of the superficial epithelium which can progress to deeper lesions and areas of erosion and ulceration4.

Diet and exercise have consistently been shown to play a major role in the development of squamous disease 5–9. In horses prone to squamous disease, grain feeding should be eliminated from the diet to reduce the production of volatile fatty acids 5. For horses in heavy work, or those that require additional calories, oils provide a safer alternative to cereals. In a study conducted in ponies, corn oil supplementation (45ml/day for 5 weeks) was beneficial to gastric health and was shown to decrease gastric acid production and increase prostaglandin production10. Maize (corn), vegetable or canola oil can all be used at up to 1 ml/kg body weight per day. Oil should be gradually introduced over a few weeks to allow the horse’s metabolism to adapt. Horses should receive supplementation with vitamin E (2000 iu/day) when feeding oil, to mitigate the potential for oxidative injury due to increased free radical production.

Feed deprivation has also been shown to cause an increase in gastric acidity, a reduction in intraluminal pH and the development of squamous disease9. A study conducted on racehorses in Australia demonstrated that those with free access to pasture were 3 times less likely to have squamous disease 11. A 2015 consensus statement 1 also recommended free access to good quality grass pasture or frequent feeding of hay (4-6 meals/day) to help restore the normal stratification of gastric pH. In one study, feeding straw as the sole roughage source increased the prevalence of squamous 5, however a recent study indicated that a 50% straw diet would not cause gastric ulcers to develop 10.

Exercise causes gastric compression, disruption to the stratification of gastric pH and ‘splashing’ of acidic fluid onto the squamous mucosa 12. Feeding a small amount (2-3L) of roughage prior to exercise to prevent this acid ‘splash’ would therefore seem logical to reduce the risk of squamous. As the duration of acid exposure also parallels the risk for development of squamous disease 13, horses prone to squamous disease should ideally be trained with short duration, high intensity exercise programs.

The importance of feeding a small amount of roughage prior to exercise.

Environmental factors have also been demonstrated to play a role in the development of squamous disease. Horses are herd animals and direct contact with others appears to reduce the risk of squamous 11. A rural setting and access to pasture also reduce risk 11.

In cases where risk factors are persistent (e.g. racehorses in training), the prophylactic use of oral omeprazole should be considered. A 2019 meta-analysis demonstrated that omeprazole prevented squamous disease in horses in training with only 23% of treated horses developing squamous disease, compared to 77% which were given no omeprazole prophylaxis14.

TREATMENT OPTIONS

Oral omeprazole is the only registered treatment for squamous disease and in early studies resulted in 70-77% healing of squamous lesions in racehorses in training 15–18. There has been a growing appreciation of the influence of diet and compliance on the efficacy of oral omeprazole 19. The absorption of omeprazole is affected by feeding and administration on an empty stomach improves bioavailability 20. Omeprazole treatment should therefore be administered after an overnight fast, 1-2 hours prior to feeding.

Esomeprazole has attracted particular interest in human, and more recently equine medicine as it is absorbed more consistently and metabolised more slowly than omeprazole21. Compared to an equivalent dose of omeprazole, esomeprazole results in a more pronounced and consistent acid suppressive effects in man 22–24 and similar benefits have now been demonstrated in horses 25. Esomeprazole may therefore offer advantages over omeprazole and may be more effective for both treatment and prevention of squamous disease, particularly in racehorses where failure rates for treatment and prevention with omeprazole may be 30% and 20% respectively 2,26.

The highest rates of squamous healing are reported following the administration of an unregistered long-acting injectable omeprazole (LAIO) preparation. Intramuscular injection overcomes any issues with bioavailability or owner compliance with the administration of oral preparations. Administration of a LAIO preparation to 6 horses demonstrated the capacity of the injectable preparation to supress acid more profoundly and consistently than when the same horses were administered oral omeprazole every day27. In the treatment of squamous disease in racehorses in Australia, 100% healing was reported with LAIO after only 2 injections one week apart 27. In a retrospective study performed in the UK, 93% healing of squamous lesions was observed with 4 weekly injections of LAIO with most cases having healed within 2 weeks after only 2 injections 28.

GLANDULAR DISEASE

RISK FACTORS AND MANAGEMENT

Unlike the squamous mucosa, the glandular epithelium has several mechanisms to protect it from injury by hydrochloric acid. The pathogenesis of glandular disease is poorly understood but it has been hypothesised that failure of normal defence mechanisms may predispose the glandular mucosa to injury29. We now know that how we manage squamous disease cannot simply be applied to the management of glandular disease.

In recent years, a growing body of evidence has indicated that both physiological and psychological stress may play a role in the development of glandular 29–33. Frequency of exercise has been demonstrated to be an important risk factor; the risk of glandular disease was shown to increase 10-fold in Thoroughbreds exercised more than 5 days per week 32. Another study in Canadian showjumpers found a 5-fold increase in risk of disease in horses exercised more than 6 times per week 33. It has been postulated that the frequency of exercise may negatively impact gastric blood flow, thereby impairing the normal protective mechanisms of the gastric mucosa. There is evidence that limiting exercise to up to 5 days per week may reduce the risk of glandular disease 29.

Trainer has been identified as a risk factor for the development of glandular disease in Thoroughbreds 32 and in a riding horse population having a greater number of handlers and riders was associated with a greater risk of disease 34. Measures to minimise stress should be tailored to each individual as the effectiveness of specific interventions will vary widely between horses.

Mucosal protectants such as pectin and lecithin complexes may be beneficial in the prevention of glandular disease 29,35. Lecithin is a phospholipid and pectins are highly viscous substances which may aid to stabilise the protective mucus layer35 of the glandular mucosa, however robust clinical trials to prove their efficacy are lacking.

TREATMENT OPTIONS

There are currently no medications registered for the treatment of glandular disease and oral omeprazole is considered ineffective29 with healing in less than 50% of cases being reported 36,37. Whilst acid injury is not thought to initiate glandular, a low pH may perpetuate mucosal injury and prevent healing1. As a result, acid suppression remains the cornerstone of therapy for glandular disease and a number of different options including, omeprazole and sucralfate combination, LAIO, esomeprazole or misoprostol are currently being utilised.

Oral omeprazole and sucralfate in combination has been reported to result in glandular healing rates of between 20-71%38–40. In some populations the response to this combination is disappointing and the combination may also present practical challenges regarding the administration of both medications at different times on an empty stomach as the absorption of oral omeprazole may be affected both by feeding and the administration of sucralfate 41,42

Like squamous disease, the highest rates of healing of glandular disease have been reported following the use of LAIO 43,44. LAIO also overcomes compliance and bioavailability issues that is associated the administration of daily, oral medications 29,42. After 2 weeks of treatment with LAIO, 9 of 12 horses were reported to have healed in a study of racing Thoroughbreds 27. In a retrospective study in the UK, rates of glandular disease healing after 4 weeks of treatment were 82% with LAIO compared to 50% with oral omeprazole 44. In a study performed at Avon Ridge Equine Veterinary Services, the administration of LAIO every 5 days versus every 7 days increased rates of glandular disease healing from 82% to 97%. Link to the study can be found here.

Injection site reactions have been reported following the use of LAIO, however in this study our rates of adverse events was 1.2% (four localised injection site reactions out of 328 injections). Our practice protocol recommends only the gluteals are used when administering LAIO (alternating sides for each injection). The total dose should be administered into a single site following thorough cleaning of the injection site. Refer to our YouTube video (below) for how we recommend administering LAIO. We DO NOT recommend splitting the dose between sites. Avoid injection into the neck or pectorals.

Esomeprazole is being used with increasing frequency in equine practice as a first-line treatment for horses with glandular disease45 and to facilitate healing of both squamous and glandular lesions which failed to respond to oral omeprazole 46.

A study performed at Avon Ridge Equine and published in UKVet which reported 75% healing of glandular disease in seven horses.

Misoprostol has been reported to result in healing of glandular in 55-72% cases 38,47, however in one report 42% of cases treated with misoprostol, squamous disease either developed or worsened 47. There are significant human health and safety concerns with the use of misoprostol and it needs to be handled very carefully.

CONCLUSION

Optimising diet and management are fundamental to the prevention and management of gastric disease. Careful consideration should be given to the constituents of the diet, the timing and frequency of feeding, exercise routines and there should be a focus on minimising stressors. Acid-suppressive medications remain the cornerstone of therapy for both squamous and glandular disease. Whilst oral omeprazole has been proven effective for the management of squamous disease it is largely ineffective for the treatment of glandular disease. New (mostly unregistered) alternatives are being explored and show promise in improving healing rates of both conditions.

The only way to tell IF your horse has gastric disease and what TYPE of disease it has, is to gastroscope your horse. We offer a mobile gastroscopy service, allowing us to scope your horse on your property.


Book An Appointment Today.

For more information, please don’t hesitate to contact us on 0427 072 095 or email info@avonridgeequine.com.au

REFERENCES:

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  2. Sykes BW, Hewetson M, Hepburn RJ, Luthersson N, Tamzali Y. European College of Equine Internal Medicine Consensus Statement–Equine Gastric Ulcer Syndrome in Adult Horses. J Vet Intern Med. 2015 Sep;29(5):1288 1299.
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  43. Sykes BW, Kathawala K, Song Y, Garg S, Page SW, Underwood C, et al. Preliminary investigations into a novel, long‐acting, injectable, intramuscular formulation of omeprazole in the horse. Equine Vet J. 2017 Nov;49(6):795–801.
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