Larry Roth, Ph.D., PAS

Conklin Co. Inc

Gastric ulcers are an increasing problem in equine athletes which results in performance and economic

losses. Research studies suggest that 50 to 90% of horses within various disciplines may suffer from ulcers.

Stomach anatomy, feed ingredients, management practices and horse temperament are some of the

factors cited as causes for the high incidence of stomach ulcers. Understanding equine stomach anatomy

and ulcer risk factors will help identify potential management responses to resolve gastric ulcers in horses.

Approximately 80% of equine gastric ulcers occur in the promixal (front part) stomach, which is less

resistant to digestive acids than the distal, or latter, part of the horse’s stomach. The distal stomach has a

bicarbonate-rich mucus layer for protection, an extensive capillary network and a rapid ability for healing.

The equine stomach constantly secretes digestive acids, and the continuous exposure to the acids is the

primary cause of gastric ulcers in horses. Bacteria residing in the stomach ferment readily hydrolysable

carbohydrates (starch), and in turn secrete volatile fatty acids (VFA). The VFA are absorbed by cells lining

the stomach, which then swell, die and finally ulcerate. The combination of hydrochloric acid (HCl), a low

stomach pH, organic acids from fermentation, and the protein-digesting enzyme pepsin act together to

cause gastric ulcers.

A research study indicated that horses running on a treadmill had increased abdominal pressure and

decreased stomach volume. Stomach contractions may push gastric acid from the distal part to the lessprotected,

promixal region of the stomach. Consequently, frequent exercise would regularly bathe the

proximal stomach in acids for destruction of the stomach lining. Ulcer incidence and severity rises as

exercise intensity increases.

The horse’s digestive tract is designed for grazing and the continual feeding and flow of saliva and ingesta

to buffer the stomach. Intermittent or irregular feeding reduces saliva flow and allows the stomach to“sit

empty”for various periods of time, resulting in a drop in gastric pH and exposure of the stomach lining to a

more acidic environment.

High-starch diets are partially fermented in the stomach by bacteria, resulting in VFA, which combined with

low-pH conditions in the stomach can damage the gastric lining. A research study compared a high-protein,

high-calcium diet of alfalfa and grain to a low-protein, low-calcium bromegrass and grain diet for ulcer

incidence. Horses fed the alfalfa and grain diet had a higher stomach pH, resulting in fewer and less severe

gastric ulcers compared to the horses receiving the bromegrss and grain diet.

Transportation increases the incidence of gastric ulcers in horses. Horses risk dehydration, immune

suppression, respiratory or digestive illnesses and other challenges while being transported. Water and feed

deprivation lower stomach pH. Transport stress interacts strongly with the other risk factors, including heat

stress.

Stall confinement changes a horse’s sociological behavior and feeding pattern. Exposure to other horses

can have a calming effect with most horses. The risks from intermittent feeding have been previously

discussed.

The NSAID decrease mucosal blood flow, decrease mucous production and increase HCl secretion. This

combination of factors leads to a stomach lining less able to protect itself in a lower pH environment.

The role of Heliobacter species in gastric ulcers is well-documented in humans, yet less certain in horses.

The use of antibiotics to control these bacteria may result in undesired complications due to shifting of the

bacteria population in favor of antibiotic-resistant bacteria.

Grazing increases saliva production and allows ingesta to be present in the stomach to absorb gastric

acids. When grazing is impractical, more frequent feeding throughout the day may produce similar results. A

shift to a high-forage diet will reduce starch fermentation and acid production in the stomach, as well as

have a more fibrous ingesta residing in the stomach. High-protein, high-calcium diets based on alfalfa hay

have reduced ulcer incidence in some studies. Forage quality should be considered to help meet the

horse’s energy needs and yet provide enough fiber for proper digestive function. Chewing long-stem hay

increases saliva flow to aid in buffering the stomach contents and lining. Research studies suggest that

supplementing vegetable oil may provide a protective lining to the stomach, while also reducing the amount

of starch fed to the horse.

Frequently transported horses need periodic rest stops to encourage water and feed consumption along

with reducing transportation stress. The diet fed prior to transporting may reduce the incidence of ulcers.

Social behavior has implication for transport and housing decisions to manage ulcers.

Veterinarians, trainers and horse owners indicate that probiotics, or known as direct-fed microbials, have

reduced the incidence of ulcers in various situations. Probiotics encourage forage utilization to enable the

feeding of a higher-forage, lower-starch diet. Reducing the amount of starch fed can lower VFA production

in the horse’s stomach.

Starch digestion in the horse’s small intestine results in glucose absorption and potentially has a negative

effect on its behavior. A horse’s behavior or calmness has been correlated to ulcer incidence. The higherforage

diet would result in fibrous ingesta remaining in the stomach for a greater proportion of the day,

which could moderate stomach pH.

Gastric ulcers occur in a high proportion of horses in various disciplines. Managing the risk factors for

gastric ulcers can improve a horse’s performance and well-being and reduce economic losses. Probiotics

can be a management tool to moderate diet and behavior factors leading to ulcers.

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Larry Roth, Ph.D., PAS is a research scientist with Conklin Co. Inc in Shakopee, MN. He researches the

nutritional and microbial needs of newborn and high-performance animals.