What conditions can we diagnose with a Gastroscope?

What conditions can we diagnose with a gastroscope?

To understand the possible pathologies of a horse’s stomach, it is important to know the anatomy and function of the stomach. The stomach of the horse normally has a capacity of 8–16 litres and is located on the left side of the abdomen beneath the rib cage. The stomach has three basic functions: storage, mixing, and breakdown of feed. Although fluid exits the stomach quickly, feed particles are retained for much longer, (up to 48 hours) while digestion is initiated. The specific anatomic arrangement between the end of the oesophagus and the stomach permits the movement of gas and fluid into the stomach, but not out of it, thereby creating a functional one-way valve. The horse’s stomach is small in comparison to the rest of the digestive system. The entrance to the stomach is the cardia and the outlet is called the pylorus. The stomach is U-shaped and has a muscular wall enabling it to contract to mix feed, with gastric secretions aiding digestion. The top third of the stomach has a nonglandular (squamous) lining, similar to that of the oesophagus. The lower two-thirds of the stomach (glandular mucosa) contain glands which secrete hydrochloric acid, pepsin, bicarbonate and mucus. The margo plicatus is the name given to the demarkation between the two.

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In an adult horse the glandular mucosa will produce about 1.5 litres of stomach fluid per hour. The stomach pH will vary between pH1.5 and pH7 depending on the region, with the lowest pH (most acidic) occurring in the glandular part of the stomach following feeding.

The main reason why we want to look into the stomach is to diagnose equine gastric ulcer syndrome (EGUS). This is a very common condition, with prevalence estimates from 25 to 50 percent in foals and 60 to 90 percent in adult horses, depending on age, performance, and evaluated populations.
EGUS is an umbrella term to describe erosive and ulcerative diseases of the stomach and this is further divided into the above described parts of the stomach: Equine Squamous Gastric Disease (ESGD) and Equine Glandular Gastric Disease (EGGD). Around 80% of gastric ulcers appear in the upper squamous compartment, as the epithelium here is not well protected against stomach acid. Ulcers are further graded 0-4 depending on their severity.

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Several risk factors have been associated with an increased risk of EGUS including diet, intense exercise, physical stress/illness, psychological stress and certain medications. EGUS can cause various clinical signs that vary immensely in terms of severity and presentation.
Foals
- Episodes of colic usually after suckling or eating
- Lying down more often
- Intermittent nursing
- Diarrhoea
- Reduced appetite
- Grinding of teeth
- Excess salivation.

Adult Horses/ Ponies
- Reduced appetite
- Dullness
- Behaviour changes
- Discomfort when the girth is tightened
- Poor performance
- Rough hair coat
- Weight loss
- Low-grade colic.

Because these clinical signs are quite vague and often go unrecognised, it is important to confirm the diagnosis by a gastroscopic exam. The scope can be used to visualise lesions in the wall of the stomach, which allows the vet to localise and grade the ulcers. These findings are important to start the horse on the right treatment course and allow for monitoring of the response to treatment over the following weeks.

Another reason to perform a gastroscope is to check for bot fly larvae (bots) from the Gasterophilus spp. flies. The yellow/orange eggs laid by these flies are commonly seen on the hair of the inner legs and knees of horses. When the horse licks or bites at these areas they ingest these eggs. The larvae hatch out of the eggs and can stay embedded in the mucosa of the tongue or mouth for approximately one month. After this time they will pass to the stomach. Once in the stomach they attach themselves to the stomach lining using ‘oral hooks’ (commonly they are found in the region of the margo plicatus) and remain there for a further 8 to 10 months before being passed out in the manure to complete their lifecycle. A heavy burden of bots can cause erosive and ulcerative lesions causing a mild gastritis, however in the majority of cases they don’t cause any problems. A good worming program is important to prevent a large infestation, and this parasite is usually targeted in spring and autumn treatments. In addition, eggs can be safely removed from the hair with a grooming tool called a bot knife. Cleaning up manure and regular application of fly repellant will also help reduce the chances of a heavy infestation.

Bot fly larvae in the horse stomach

Bot fly larvae in the horse stomach

A gastroscope can also be used to diagnose an impaction of feed material in the stomach. On occasion, horses that eat very fast or do not drink enough water or eat feed that tends to swell after ingestion, can get a gastric impaction. This is an overfilling of the stomach and the food does not pass into the duodenum resulting in discomfort and signs of colic. An inability to pass a nasogastric tube or poorly digested food coming back up through the tube can be an indication, however a gastroscope will confirm the diagnosis by allowing visualisation of the large amount of impacted food in the stomach. A stomach impaction will usually be treated by administering fluids via nasogastric tube. This procedure may need to be repeated several times before the impaction is resolved.

Although much less common, it is also possible to diagnose gastric tumours on gastroscopy. Most gastric tumours are squamous cell carcinomas, and in the majority of cases these have been found in middle aged to older horses.
Symptoms are often vague and the main clinical sign is chronic weight loss. Treatment is generally not attempted because unfortunately by the time it makes the horse sick, the tumour is in such an advanced stage that the prognosis is very poor. Gastroscopy is a safe and effective procedure for examination of the oesophagus, stomach and proximal duodenum, allowing a rapid diagnosis of a variety of conditions that often have vague and non-specific clinical signs.

Zoe Meyer