By
Christina Ellis, DVM, DACVS
The
equine stomach is divided into two portions; it is lined dorsally by stratified
squamous epithelium (non-glandular) and ventrally by glandular
epithelium. The division between these two portions is the margo
plicatus. The non-glandular portion of the stomach essentially functions
as a reservoir for food and has no secretory or absorptive function. The
glandular portion of the stomach is similar to the lining of the stomach of
humans and some other animals. This portion secretes hydrochloric acid,
pepsin, electrolytes, and water. The glandular lining contains a mucus/
bicarbonate barrier that protects itself from the acidic environment and has
growth factors that promote mucosal healing. The non-glandular lining, on
the other hand, does not have any protection from acidic injury. Eating
stimulates secretion of bicarbonate-rich saliva that helps neutralize gastric
acid, and the roughage itself absorbs the secretions. These are the only
defense mechanisms for the non-glandular epithelium. Hydrochloric acid is
continuously secreted from the stomach, even when the horse is not
eating. If food is withheld from a horse, lesions can develop in the
non-glandular mucosa within 24-48 hours due to the contact with hydrochloric
acid.
Gastric
ulceration is the most common disorder of the equine stomach. It is influenced
by the management and use of the horse. The occurrence of ulcers has been
reported as high as 60% in show horses and as high as 90% in racehorses. Horses
turned out onto pasture and exercised lightly typically have normal stomachs or
only very mild erosions. In contrast, horses kept in box stalls and trained
intensively have a high occurrence of significant gastric lesions. It has been
shown that the severity of the lesions corresponds with the intensity of
exercise. Stress, such as hauling and mixing groups of horses, can increase the
likelihood of ulcers. Furthermore, restricting access to roughage or feeding a
large amount of concentrate promotes increased acidity of the stomach, thereby
damaging the non-glandular mucosa.
Signs
of gastric ulceration can be vague and non-specific. These horses may show
abdominal discomfort, indicated by mild-to-moderate colic and frequent laying
down. They may also have poor appetite, poor body condition, poor hair coat,
attitude changes, and decreased performance. The severity of these signs does
not indicate the severity of the lesions. Horses with superficial erosions may
have significant discomfort, whereas horses with deep, bleeding ulcers may have
mild clinical signs.
Gastroscopy
is the only method of definitively diagnosing gastric ulceration. A 3-meter
endoscope is passed into the nostril and down the esophagus into the stomach
for visualization of the gastric mucosa. Most lesions are identified in the
non-glandular mucosa, adjacent to the margo plicatus along the right side or
the lesser curvature of the stomach. More severe cases may have larger
ulcerations extending dorsally, towards the top of the stomach. Lesions are
rarely identified in the glandular portion of the adult equine stomach.
Glandular lesions can form due to administration of nonsteriodal
anti-inflammatory medications (phenylbutazone [Bute], flunixin meglumine
[Banamine]). These medications compromise the protective mechanisms of the
gastric mucosa, leading to ulceration.
A
variety of medications are available for treatment of gastric ulcers. Decisions
on which medications to use depend on the location of the lesions, the severity
of the lesions, and the financial constraints of the owner. The best treatment is
proton pump inhibitors, such as omeprazole (Gastrogard). This class of drug
binds to the proton pump and inhibits the secretion of hydrochloric acid. It
has proven very effective in healing gastric ulcers, including horses that
remain in race training. It is available as a paste and only needs to be
administered once daily. The next class of medication is histamine type-2
receptor antagonists. This includes ranitidine (Zantac), cimetidine (Tagament),
and famotidine (Pepcid). These drugs bind to the receptors on the gastric
cells, and also inhibit secretion of hydrochloric acid by a different mechanism
than proton pump inhibitors. They reduce gastric acidity for 1-8 hours, and are
therefore dosed for administration three times daily. There is variability among
horses in the magnitude and effect of this drug, which makes its effectiveness
less predictable. When effective, however, these drugs are significantly
cheaper than proton pump inhibitors. Another class of drugs is antacids, such
as magnesium oxide and aluminum hydroxide (Maalox, Mylanta). Antacids
neutralize gastric acid but only for a brief period of time (30-120 minutes)
and need to be given in large volumes to be effective. Thus, antacids are not a
practical treatment option. Finally, sucralfate, a mucosal adherent, is unique
in that it is beneficial for treatment of glandular ulcers. Sucralfate acts as
a “band-aid” and binds to the gastric glandular mucosa. It enhances mucus
production, mucosal prostaglandin synthesis, and mucosal blood flow. Sucralfate
is not recommended for the typical adult horse with non-glandular gastric
ulcers and should be reserved for horses with glandular lesions.
The
ideal preventative measure for gastric ulcer formation is to cease exercise
training and turn the horse out onto pasture. However, this is not feasible in
most situations. Some horses appear to develop ulcers more readily than others,
and these horses are more likely to have recurrence after successful treatment.
Feeding management can be modified to promote more continuous roughage
consumption and less concentrate consumption, which will help reduce the
gastric acidity. It has been suggested that alfalfa hay is superior to grass
hay for prevention of ulcers due to the high protein content, which may buffer
the acidic environment. More recently, omeprazole has been dosed for prevention
of gastric ulcers and marketed under the name Ulcergard. It has been found to
be effective at prevention of gastric ulcers in horses undergoing intensive
race training, whereas other treatments such as ranitidine have shown to be
ineffective in these cases.
Horses
suspected of gastric ulcers can be easily diagnosed with gastroscopy and
effective treatment can be initiated. Performing repeat gastroscopies are
beneficial to assess the effectiveness of the treatment and the progression of
healing. Once the lesions are healed, measures should be taken to prevent
recurrence.
Contact
Surgi-Care Center for Horses at 813-643-7177 or email lkuebelbeck@surgi-carecenter.com with
any questions regarding this topic.
This article was originally published in Horse & Pony magazine and is reprinted with their permission.