Horse in Pain with Weight Loss
History. A 4-year-old Thoroughbred mare presents for weight loss, inappetence, grinding of teeth, and low-grade colic. She is off the track now but was winning until I month ago, and thus the trainer is concerned.
Clinical Examination. The mare seems to be quieter than expected. Her temperature, pulse, and respiration are normal. She appears thin for a horse from the track, and the trainer thinks the mare has lost IOO to 150 pounds in the last month. Her hair coat is poor. Your examination reveals no other abnormal findings.
With this history, gastric ulcers are a likely differential diagnosis. You discuss this with the trainer and decide to perform gastroscopy before doing any other diagnostic tests.
Comment. On endoscopy the mare has several ulcers along the junction of the squamous and glandular sections of the gastric epithelium. In addition, she has two large and a few small ulcers on the nonglandular squamous compartment of the stomach. The squamous epithelium of the equine stomach has no mucus-secreting glands, in contrast to the glandular mucosa. The thick alkaline mucus that coats the glandular surface is an important component of the stomach epithelium’s natural defense against acid damage. The lack of surface mucus makes the squamous portion of the equine stomach particularly prone to ulcer development. Ulcers are likely the cause of this horse’s weight loss, colic, and poor performance. She will be treated, and her management will be modified to encourage healing of the ulcers.
Horses continuously secrete hydrochloric acid (HCl) in the stomach, in contrast to many other species that can modulate acid secretion based on food intake. Horses are thus suited to be constant grazers with access to food 24 hr∕day. This mare is kept in the stall 24 hr/day unless she is being worked, and she is given a high-grain low-hay diet. Thus, she eats two high-grain meals per day, and she only has a small amount of grass hay, which she typically eats quickly.
When horses do not eat, the pH of the stomach decreases rapidly. Furthermore, being inside all the time adds to her stress, making this mare more prone to gastric ulcers. Histamine and gastrin also stimulate HCl secretion, whereas somatostatin inhibits it. Therefore, treatment is multifactorial, aimed at changing the management to increase the pH of the stomach as well as administering drugs to help decrease acid secretion.The parietal cells secrete HCl through H+,K*-ATPase (proton pump). Omeprazole, a once-daily medication, inhibits the proton pump. Other anti-ulcer medications include histamine type 2 receptor antagonists, such as cimetidine and ranitidine, which block histamine attachment to stimulatory receptors on the surface of parietal cells, decreasing HCl release. Another way to protect the stomach from acid damage is to coat the gastric lining with medications such as sucralfate, which forms a protective barrier between the mucosa and luminal contents.
Treatment. A common treatment choice in this case currently is omeprazole, which specifically decreases HCl secretion. Treatment depends on the severity of the ulcers and the inciting cause. In many cases, treatment may be recommended for up to 28 days. Additional management changes to enhance healing would include increasing the time per day the mare spends eating. Pasture would be ideal, particularly alfalfa forage, which has inherent buffering capacity. Gradually decreasing the amount of grain fed daily and increasing the amount of forage would also be beneficial. Although these management changes are ideal, they can be difficult to maintain because of the typical management of these horses.