Stomach ulcers are caused by excess stomach acid, often produced as a result of stress. The discomfort from stomach ulcers may lead to certain changes in your horse’s behavior. Signs include a change in eating or drinking habits, weight loss, dull hair coat, recurring colic, poor performance and overall poor attitude. The excess acid often results in lesions in the gastric mucosa (stomach lining). Ulcers can occur in the upper squamous region or the lower glandular region of the stomach. It is important to distinguish between squamous ulceration and glandular ulceration.