Q: What are the clinical signs of ulcers in a horse? Will a horse’s behavior change dramatically if he has gastric ulcers?

A: Gastric ulcers can change a horse’s behavior and make them reluctant to work. These are typically the first signs of gastric ulcers that horse owners notice and relate to the pain from the gastric ulcers, but the pain is usually not severe enough that they show it all the time—they might only show it during certain activities.

One of the things we know is that there are two types of gastric ulcers. The gastric ulcers that occur in the upper part of the horse’s stomach, or what we call the squamous epithelium. Squamous ulcers are caused by acid splashing up on that part of the stomach because that part of the stomach doesn’t have adequate protection against acid.

Squamous ulcers can be exacerbated by infrequent meal feedings rather than constant access to food and exercise, which can cause the acid to splash on that part of the stomach. This is why we often see behavior changes and signs of pain or discomfort under saddle. These horses might also show unhappy or aggressive behaviors when they’re being tacked up, in anticipation of the pain.

The other types of gastric ulcers occur in the lower part of the stomach, or the glandular mucosa. The causes of these ulcers are less well understood but possibly could relate to decreased blood flow to this part of the stomach that impairs its healing ability. Clinical signs of glandular ulcers can also include behavior changes or decreased willingness to work, or possible recurrent mild signs of colic unrelated to work.

Horse owners should keep in mind that hay is less stimulating for acid production than grain and, so, a lot of times owners comment that horses eat their hay totally fine but start to not want their grain. They might not eat it at all or might just not finish it.

It is less common for an adult horse to have colic signs from gastric ulcers, but it is possible. I’ve seen bad gastric ulcers cause colic although, again, the signs of colic are usually more mild.