ANS 150 Equine Diseases

What part of the equine GI tract is the stomach considered?

The foregut

What does the equine stomach do?

• It acts as a digestive organ

• produces acid continuously

• supports bacterial fermentation

• secretes digestive enzymes

Why do horses produce stomach acid continuously?

Horses are naturally continuous grazers, so their stomach is adapted to ongoing food intake

Why does roughage help protect the equine stomach?

Roughage buffers stomach acid and helps form a food bolus

What is the protective role of long-stem roughage?

It buffers acid and helps reduce acid splash onto squamous stomach area

What are the two major regions of the equine stomach?

• squamous/ non-glandular

• glandular

What separates the squamous and glandular stomach?

The margo plicatus

Where is the squamous stomach located functionally?

It connects with the mouth and esophagus

Why is the squamous stomach vulnerable to ulcers?

It is not accustomed to acid exposure

Where is the glandular stomach located functionally?

It connects toward the duodenum/small intestine

What cells secrete acid in the glandular stomach?

Parietal cells

Why is the glandular stomach normally more protected from acid?

• It has a thick mucus layer

• robust blood flow

• buffers

How does stomach acidity change as you move ventrally?

pH decreases; the stomach becomes more acidic

What is a food bolus?

A mass of feed/roughage in the stomach that helps buffer acid and reduce acid splash

What is a gastric ulcer?

A break in the lining of the stomach

What is EGUS?

Equine Gastric Ulcer Syndrome

What are the two main types of EGUS?

• Equine Squamous Gastric Disease

• Equine Glandular Gastric Disease

What are the two categories of ESGD?

• Primary ESGD

• Secondary ESGD

What is primary ESGD usually associated with?

Management factors, especially feeding and housing practices that increase acid exposure

What is secondary ESGD usually associated with?

Gastric outflow obstruction or hospitalized/sick horses with gut motility problems

Why is squamous ulceration common in domesticated horses?

Feeding and housing practices often reduce continuous grazing and increase acid exposure

Why do wild horses have less acid splash despite running?

They eat continuously and maintain a food bolus that helps prevent acid splash

Why can glandular ulcers occur even though the glandular lining is normally exposed to acid?

They may result from breakdown of normal defense mechanisms that protect the lining

Is bacterial infection clearly associated with glandular ulcers in horses?

No, do not have clear helicobacter-type association noted

What human risk factors are associated with ulcers but are not the same in horses?

• Helicobacter pylori

• NSAID use

Why is EGGD less well understood?

The glandular lining is normally acid-exposed, so ulcers likely involve failure of protective mechanisms rather than simple acid exposure

How can exercise contribute to squamous ulcers?

Gaits faster than a walk increase intra-abdominal pressure, pushing acid upward onto the squamous lining.

Why do racehorses have more ulcers?

Intense and long-duration training increases acid exposure and ulcer severity

How is ulcer severity related to endurance riding?

Severity is directly correlated with the distance of the ride

Who gets gastric ulcers?

Risk varies by breed, use, training level, and type of ulceration

What percentage of Thoroughbred racehorses may have ESGD?

About 80–100%

What percentage of show/sport horses may have ESGD?

About 17–58%

What percentage of Australian Thoroughbred racehorses may have EGGD?

About 47–65%

What percentage of sport horses may have EGGD?

About 64%

Are gastric ulcer risk factors simple or multifactorial?

Multifactorial

Why might horses trained in urban areas have higher ulcer risk?

They may have less turnout and more confinement/stress

How does lack of pasture turnout affect risk?

It reduces grazing and food bolus formation, increasing acid exposure

What nutritional factors increase ulcer risk?

• Lack of forage

• more than 6 hours between forage meals

• straw alone as forage

• high starch/grain intake

• intermittent water access.

Why is alfalfa beneficial for gastric ulcer prevention?

It helps raise gastric pH because it contains calcium and protein that buffer stomach contents

Why does high starch/grain intake increase risk?

Breakdown can produce volatile fatty acids, adding to the acid load in the stomach

Why is intermittent water access a risk factor?

Less water can make stomach contents more concentrated and acidic

Are there pathognomonic clinical signs for EGUS?

No. Clinical signs are nonspecific

What does pathognomonic mean?

A sign that is specific to one disease and strongly indicates that disease

What are common clinical signs of gastric ulcers?

• Decreased appetite

• poor body condition

• weight loss

• colic after eating

• cinchy/girthy behavior

• behavior changes

• poor performance

• poor coat condition

What behavior changes may be seen with gastric ulcers?

Stereotypic behavior, aggression, or self-mutilation

Is diarrhea a typical sign of gastric ulcers?

No. It is anatomically and physiologically implausible for stomach ulcers.

What is required for definitive diagnosis of EGUS?

Gastroscopy

What length endoscope is usually needed for mature horses?

At least a 3-meter endoscope

What route does the gastroscope take?

Through the esophagus/cardio region into the stomach, with visualization of squamous, glandular, pyloric, and sometimes duodenal areas

What does squamous stomach tissue look like on gastroscopy?

Light pink

What does glandular stomach tissue look like on gastroscopy?

Darker pink

Is there a relationship between the presence of ESGD and EGGD?

No. One does not predict the other, which is why both need to be examined

How is ESGD graded?

From Grade 0, normal, to Grade 4, severe/deep ulceration.

Should EGGD be graded?

No. EGGD grading has minimal validity.

Why should EGGD not be graded?

Visual severity and microscopic appearance correlate poorly, and appearance/contour varies.

What is polypoid ulceration?

A glandular ulcer pattern seen commonly in Warmblood horses

What is omeprazole used for?

It blocks acid production

What are common brand names for omeprazole in horses?

• Gastrogard

• Ulcergard

What did ranitidine do?

• It decreased acid production

• unavailable

What does sucralfate do?

Coats the stomach lining and increases blood flow

What is another name for sucralfate?

Carafate

What is misoprostol used for?

It is a synthetic prostaglandin analog used especially for glandular ulcers

How does misoprostol help glandular ulcers?

It increases blood flow to the gut and supports healing

What are prokinetic agents used for?

Secondary ulcers related to gut motility/transit issues

How do prokinetic agents help?

They increase gut transit and move acid/bile along

Why is management change necessary in ulcer treatment?

Medication alone may not prevent new ulcers if risk factors continue

What management changes help prevent recurrence of gastric ulcers?

• Pasture grazing

• high forage intake

• some alfalfa

• lower concentrate diets

• smaller frequent meals

• ad libitum forage

• small forage before exercise

• constant water access

Why feed a small amount of forage before exercise?

It creates a food bolus to reduce acid splash

Why lower concentrate diets?

They decrease intragastric fermentation and acid load

What is the main caution with supplements for ulcers?

Many lack strong randomized clinical control studies

What may sea buckthorn berry extract help with?

Glandular ulcers but did not improve squamous ulcers in study

What effect can oils such as canola have?

They may lower gastric acid output because of it has an omega 3:6 ratio which is has anti-inflammatory effects

What do antacids do?

They may increase gastric pH but need to be given every 2 hours

When might antibiotics/probiotics help?

Possibly with non-responsive ulcers

What do pectin-lecithin complexes do experimentally?

Increase total mucus concentration in gastric juice

What supplement combination has shown promise as prophylaxis for ESGD and EGGD?

• Magnesium hydroxide

• pectin-lecithin complex

• Saccharomyces cerevisiae

What is strangles?

A contagious respiratory infection of horses caused by Streptococcus equi equi

What organism causes strangles?

Streptococcus equi equi

Why is it called “strangles”?

Swollen lymph nodes can compress the trachea and interfere with breathing

What does severity of strangles depend on?

The horse’s immune status

How do older horses usually respond?

They tend to have less severe disease

When does fever occur after exposure to strangles?

About 3–14 days after exposure

What are common clinical signs of strangles?

• Fever

• snotty nose

• swollen/abscessed submandibular or retropharyngeal lymph nodes

• sore throat/pharyngitis

• lethargy

Which lymph nodes commonly swell or abscess with strangles?

• Submandibular

• retropharyngeal

What emergency airway procedure may be needed if swelling prevents breathing?

Tracheostomy

Why might intubation be difficult in severe strangles?

Hard lymph node abscesses and swelling can obstruct the airway

How is strangles spread?

By nasal shedding

When does nasal shedding start?

About 2–3 days after fever begins

How long does shedding usually persist in most horses?

About 2–3 weeks

Can horses shed after appearing recovered?

Yes. Some horses shed longer after recovery

What percentage of horses may become long-term subclinical carriers?

About 10%

Where do long-term carriers often harbor bacteria?

The guttural pouch

What is chronic empyema?

Chronic accumulation of pus, especially in the guttural pouch

What are chondroids?

Hardened pus “stones” that can form with chronic empyema.

What signs may long-term carriers show?

rare but:

• Sporadic cough

• intermittent nasal discharge

What percentage of horses develop solid immunity after strangles?

About 75%

How long can immunity last after strangles?

Around 5 years or longer

Does Streptococcus equi equi readily persist in the environment?

No. Good sanitation reduces spread

What samples can be used to diagnose strangles?

• Nasal swabs

• nasal washes

• pus from abscesses

What does PCR detect in strangles diagnosis?

bacterial DNA dead or alive