Gastric Ulceration in Horses – What Can We Do?

Very roughly speaking, the stomach is situated halfway down between the back of the withers and the elbow of the horse. It sits behind the liver and in front of the intestines. Functionally it is a ‘balloon’ between the oesophagus (swallow tube) and the intestine, and food that was eaten is held here before it is being passed in a constant stream of small amounts to the small intestine.

The digestion/breakdown of food starts in the mouth, where the chewing by the teeth breaks down the largest particles, and enzymes in the saliva start the digestive process. Saliva is secreted more when the horse is chewing, so a horse being fed fibre does produce more saliva. Further breakdown of food particles takes place in the stomach with help of further enzymes, secreted by the stomach as well as the stomach acid, preparing the nutrients for absorption in the small intestine once passed through. The acid also serves as a way of decontaminating food by killing off some of the harmful bacteria that are not resistant to the low Ph in the stomach. Some bacteria can survive in this acidic environment, but not all bacteria are harmful, and some even play a role in the digestive process too. While doing so, depending on the sugar content of the food source, these bacteria may produce further acids in the form of VFAs (volatile fatty acids) and lactic acid. So, the bacteria and the acid do influence each other. The stomach is in constant movement, ‘kneading’ the food contents to mix with the enzymes, bacteria, and acid, and to push it through into the intestines in smaller constant quantities.

The lining of the stomach of a horse consists of two distinctively different parts. In the upper part of the stomach, we have ‘squamous mucosa’. This stomach lining is more similar to mucosa on the inside of the mouth. In the lower part of the stomach the lining is ‘glandular mucosa’ and is so called because it contains many glands that secrete the digestive enzymes, the stomach acid, and a gloopy substance that sticks to the glandular layer itself to protect it from its own acid. 

As you can see, the stomach acid does play an important role for the horse, and some acidity is needed. From research we do know that the pH of the stomach juices overall does vary according to the location within the stomach as well as at different times during the day.

Consistent with the two different types of stomach lining, we divide equine gastric ulcers in squamous and glandular ulcers, depending on in which mucosal part we find them.

ESGD – Equine squamous gastric disease describes gastric ulcers in the squamous mucosa. They can develop relatively quickly when this part of the stomach lining comes into contact with gastric acid. There is always a pool of some fluid including stomach acid in the bottom of the stomach, even when a horse is not anticipating food or has just eaten. Without any protection of the top half of the stomach, as you can imagine, this acid would splash up during exercise of the horse. For this reason squamous ulcers are sometimes called ‘splash ulcers’ especially if we find them in a ‘splash’ pattern just above the margot plicatus which divides the lower (self-protecting) part of the stomach lining from the upper (unprotected) part of the stomach lining. One way to protect this upper part of the stomach lining is by feeding the horse constant fibre (hay, chaff etc) and especially before exercise, so that the ‘matt’ of fibre floats/sits on top of the stomach fluids and prevents splashing. Also, the increased production of saliva will in part buffer the stomach acid to be less acidic so less harmful to the unprotected stomach wall. 

Horses that have no access to fibre or do not eat it, especially right before vigorous exercise, are most at risk of developing these ulcers.

EGGD – Equine glandular gastric disease describes gastric ulcers in glandular mucosa. The glandular mucosa is the lining of the lower part of the stomach, where the stomach fluids and acid sit, produced by this glandular mucosa which also produces a gloopy substance sticking to the mucosa as a barrier for the acid, so the exposure of the mucosa itself to the acid is limited. Ulcers can develop in this area if the protective layer is not produced properly or is broken down. The exact mechanisms for this are unknown, but it is thought that lots of alfalfa or straw (very stalky fibre mechanically breaking the barrier down), bacterial balances in the stomach (bacteria breaking the substance down), certain drugs (chemical impact on the barrier) can be the cause for it breaking down, and that reduced blood flow through the stomach wall (due to certain medications, hormonal alterations or stress) could cause lesser production of this layer.