Inside the stomach

To understand these two conditions, it is useful to recap on how the stomach works. A horse’s stomach is a single chamber that has two main regions: the squamous mucosa (non-glandular), which occupies the top portion of the stomach, and the glandular mucosa inhabiting the bottom portion and exit (pyloric region) of the stomach. The non-glandular region doesn’t have glands and therefore does not produce gastric acid, nor does it have a protective mucous lining. The glandular region, however, does produce both gastric acid and mucous, which protects the cells from gastric acid injury. The two sections are distinguished by a line that defines the two called the margo plicatus.

Gastric disease can develop in one or both regions of the stomach, and one can develop without also being present in the other.

While squamous ulcers can occur throughout the non-glandular mucosa, the most commonly affected region is the area just above the margo plicatus. Similarly, glandular ulcers can occur anywhere in the glandular mucosa, but the most common location is the glandular mucosa of the pylorus (exit of the stomach).

Squamous disease

Primary squamous ulceration occurs as a result of acid damage to the non-glandular lining. Causes include intense exercise, high concentrate/low forage diets, starvation, water restriction, and overuse of electrolytes.

The feeding strategies used for managing squamous ulceration include ensuring horses have access to a highfibre diet ad lib and that they actually eat it (see box, p74). Feeding concentrate feeds isn’t a problem in itself, as long as they are fed in conjunction with plenty of fibre and the amount of non-structural carbohydrate (sugar and starch) in the feed is minimised.

Exercise is also an important factor for squamous ulcers. When a horse exercises acid is pushed up onto the squamous mucosa, so the longer the horse exercises, the more damage is done. Over the course of a week, the total number

of minutes a horse spends at trot, canter or gallop will contribute to the risk of squamous disease.

Glandular disease

The exact causes of glandular ulcers remain unclear, although one theory is that there is a failure in normal defence mechanisms against the acid. Exercise is also significant in relation to glandular ulcers, but for these ulcers it’s the number of days exercised per week, not the intensity or duration that is relevant.

In one study, showjumpers exercised six or seven days a week were found to be three-and-a-half times more likely to have glandular disease than horses exercising five days or less per week. A similar study looking at racehorses found that horses working five or more days had a 10-fold increase in the risk of glandular disease when compared with horses exercising four or less days per week.

This shows that rest days are important, and the current recommendation is that horses should have a minimum of two, ideally three, rest days built into their weekly routine. During training periods, it is ideally one day on and one day off, and the exercise should focus on quality rather than quantity.

Timing exercise

It’s also a good idea to feed a small haynet, ideally alfalfa hay, or a fibre-based hard feed while grooming and tacking up to buffer the stomach from acid during exercise. Exercising in the afternoon rather than the morning is ideal as this is when the horse is more likely to have been eating and have food in his stomach to buffer the gastric acidity.

Most horses don’t eat in the early hours of the morning because they are resting and sleeping, so the morning means they may have less food in their stomachs, increasing their risk of squamous disease.

The amount of chewing is also a factor — high-fibre chaffs and hay encourage more saliva production than grain or concentrate meals, which buffers acid.

Horses with glandular disease have a more pronounced cortisol response to stress testing and behavioural stress is an important contributor to glandular disease. For this reason, management includes trying to reduce daily stress, including by allowing co-habitation with other horses — without rugs on to enable mutual grooming — keeping handlers and riders consistent, and allowing an expression of natural behaviours, as well as ensuring an enriched environment.