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Equine gastroscopy: a complete perspective

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01 August 2009, at 12:00am

TONY LOCK reports on the gastroscopy training forum held during gastric ulcer awareness month

THE BEVA gastroscopy training forum held in May at b&W Equine Group's Willesley clinic, once again proved to be a huge success for all attending delegates. Run by a panel of specialist instructors, the course covered all aspects of equine gastroscopy in a very practical and informative way.

By the end of the day all delegates had managed to conquer the enigma of passing a gastroscope through the pylorus and into the duodenum. 

Equine Gastric Ulceration Syndrome (EGUS) has become an increasingly recognised problem, affecting many types of horses. 

Studies carried out by Merial Animal Health have shown an incidence of 93-100% in thoroughbred racehorses in training and up to 76% in elite event horses1,2,3. Recognition of horses affected by EGUS will not only improve the health of affected individuals but will also optimise the level of equine performance4 . 

There is a range of predisposing factors for the development of EGUS. The main three are stress, exercise and feeding practices. There are various types of EGUS involving both the squamous and glandular compartments of the stomach. 

The formation of gastric ulcers is associated with an imbalance between mucosal aggressive factors (e.g. HCL, pepsin, bile acids and organic acids) and mucosal protective factors (e.g. bicarbonate and mucus). 

How ulcers form 

The equine stomach is a single chambered structure, the top half of which is comprised of stratified squamous epithelium (non glandular mucosa) separated from the glandular epithelium at the bottom half by the margo plicatus.

Ulceration of the non glandular mucosa is related to increased acid exposure, whereas glandular ulceration results from failed mucosal defences. There is more evidence now emerging that bacteria may have an involvement in persistent glandular ulceration cases. 

Clinical signs 

Signs of EGUS in adult horses are often vague and non specific. Clinical signs include poor appetite, weight loss, poor body condition and hair coat, poor performance, behavioural changes, discomfort on girth tightening and recurrent colic.

The relationship between grade of ulceration and severity of clinical signs is not clear cut. Grading of gastric ulceration at any given time will correlate with the level of training that the horse is currently under5 . 

Diagnosis 

A three-metre flexible endoscope is necessary for performing gastroscopy in adult horses. It is useful to have a hand pump or insufflator which enables more rapid distension of the stomach with air during examinations. Having completed the procedure, a suction pump is necessary to remove the insufflated air. 

Prior to performing gastroscopy the horse should be starved for at least 12- 16 hours. Water can be left for up to 2-4 hours before. It is usually necessary to sedate the horse to facilitate the procedure. As well as someone operating the gastroscope, a competent “passer” is required, who will pass the scope up the ventral meatus and into the pharynx. 

The tip of the scope is then aimed dorsal to the arytenoid cartilages of the larynx. Pressing the flush button on the scope may help to stimulate the horse to swallow. Once the tip of the scope has been swallowed into the rostral portion of the oesophagus, it is momentarily stopped to check that it is correctly positioned and has not inadvertently retro-flexed back into the oral cavity. 

The scope is then carefully passed down the oesophagus and through the cardia into the stomach. Once inside the stomach, the scope is orientated so that the gastric fluid line is horizontal and below the endoscope. The stomach is then insufflated with air, which helps to flatten out the mucosal folds and “rounds” the stomach, easing passage of the scope around the greater curvature towards the pylorus. 

It may be necessary at this stage to wash the mucosal surface of remnant food material via a transendoscopic catheter to allow complete visualisation of both the squamous and glandular mucosal surfaces.

The margo plicatus is a readily identifiable landmark that should be utilised to orientate yourself within the stomach. The scope should then be passed along the surface of the greater curvature dorsal to the line of the margo plicatus. Eventually the lesser curvature will become visible.

By advancing the scope ventrolateral to the lesser curvature and into the dependant portion of the stomach, the antrum and pylorus will be able to be located. At the entrance to the pylorus the scope can be passed through into the duodenum for further investigation and biopsy collection if indicated. 

Throughout the gastroscopy procedure all ulcers should be graded and their location noted. Images obtained during the examination ideally should be able to be stored digitally. This will help in monitoring ulcer healing in future gastroscope examinations. Before removing the scope, all the insufflated air should be removed to avoid any patient discomfort later. 

Treatment 

The aim of medical management of EGUS is to decrease hydrochloric acid and thereby increase the pH above 4. Decreasing hydrochloric acid production will help to alleviate pain, reduce on-going damage and allow the mucosal lining to heal. 

Omeprazole (GastroGard, Merial) is a proton pump inhibitor that can reduce gastric acid secretion by 99%. The drug is administered orally at a dose of 4mg/kg per os SID (ideally 60 minutes before feeding). Treatment period is a minimum of 28 days whereupon rescoping will allow evaluation of ulcer healing. A quarter dose (1mg/kg) can be used to help prevent ulcer recurrence. 

Other anti-secretory agents include histamine (H2) receptor antagonists ranatidine and cimetidine. These drugs are administered orally three times a day and although relatively cheap, responses may vary, especially if the horse remains in full training6 . These drugs, however, are not licensed for use in the horse. 

Various agents can be used to assist mucosal healing through enhancing glandular mucosal blood flow, e.g. prostaglandin analogue PgE (Cytotec). Sucralfate (Antepsin) 10-20mg /1kg po q 8hr can facilitate mucosal healing by binding to injured glandular mucosa and enhancing both blood flow and mucus production. Corn or vegetable oil (100- 200ml/500kg bid po) is a less expensive means of enhancing mucosal defences and reducing hydrochloric acid7 . 

In some cases of squamous ulceration bacterial colonisation may occur. Improved healing may occur with the use of potentiated sulphonamide antibiotics. Pathological Helicobacter pylori has been suggested to have a role in some cases of recurrent, non healing glandular ulcers which require treatment with doxycycline (10mg/kg po bid). 

Antacids have also been utilised for treatment of EGUS. Unfortunately, horses are continuous acid secretors, so in order to neutralise acid contents treatment every 2-3 hours would be required. They do not effectively heal lesions and therefore their use is mainly restricted to prophylactic therapy. 

Management and prevention 

Management modifications in cases of EGUS mainly involve dietary changes and reduced stress through alterations in training and husbandry. 

The main dietary modification involves increased amounts of forage in the diet and for stabled horses (or those on small paddocks) multi-sited allocation of forage will help encourage more natural feeding behaviour. 

This encourages natural saliva production which helps to buffer the acid environment of the stomach. It also helps to reduce any periods of fasting and if possible concentrates should be split fed as multiple small meals. 

1. Murray, M. J. et al. (1996) Factors associated with gastric lesions in thoroughbred racehorses. Equine Vet J 25 (5): 368-374.

2. McClure, S. R., Glickman, L. T. and Glickman, N. W. (1999) Prevalence of gastric ulcers in show horses. J Am Vet Med Assoc. 215 (8): 1,130-1,133. 

3. Mitchell, R. D. (2001) Prevalence of gastric ulcers in hunter/jumper and dressage horses evaluated for poor performance. Proceedings of the Association of Equine Sports Medicine Annual Meeting. 

4. Nieto, E. J,, Snyder, J. R., Vatistas, N. J. and Jones, J. H. (2009) Effect of gastric ulceration on physiologic responses to exercise in horses. AJVR 70 (6). 

5. de Bruijn, C. M., Schutrups, A. H. and Seesing, E. H. A. L. (2009) Prevalence of equine gastric ulceration syndrome in standardbreds. Veterinary Record, 27th June. 

6. Buchanan, B. R. and Andrews, F. M. (2003) Treatment and prevention of equine gastric ulcer syndrome. Vet Clin North Am Equine Pract. 19 (3): 575-597. 

7. Cargile, J. L., Burrow, J. A., Kim, I., Cohen, N. D. and Merritt, A. M. (2004) Effect of dietary corn oil supplementation on equine gastric fluid acid, sodium, and prostaglandin E2 content before and during pentagastrin infusion. J Vet Intern Med. 18 (4):545-549.