Regurgitation and Vomiting

Bradford P. Smith

Regurgitation is the reflux of esophageal, gastric, or rumen contents into the mouth or nose. This may be caused by malfunction of the esophagus or, in ruminants, as part of the normal physiology for rechewing ingested plant fiber (Boxes 7.15 and 7.16).

Causes of Regurgitation and Reflux in Horses

Common Causes

Choke

Damaged esophagus, foreign body, or diverticulum Megaesophagus

Foreign body in pharynx, trachea, or nose

Guttural pouch infection and pharyngeal paresis with nerve involvement

Gastric dilation, impaction

Gastric rupture

Less Common Causes

Snake bite

Tetanus

Tick paralysis

Anterior enteritis (duodenitis or proximal jejunitis) Gastric stenosis, ulcers

Hydrocephalus, meningitis, encephalitis

Central nervous system trauma

Polyneuritis

Peritonitis

Persistent right aortic arch

Grass sickness (exotic)

Toxins

Phosphorus α-Naphthylthiourea (ANTU)

Cyanide

Herbicides

Arsenic

Lead

Nitrophenyl urea (vacor)

Organochlorine

Plant Toxins

Oleander

Castor bean

Death camas (Zigandenus species)

Algae

Heath (Ericaceae)

than true vomiting. Vomiting is unusual in both ruminants and horses.

Although regurgitation is a normal phenomenon in ruminants, it is unusual to find excessive regurgitation as a sign of disease.

Horses have such a marked tone at the cardiac sphincter that vomiting occurs only when extreme intragastric pressures develop, usually in small intestinal obstructive diseases or proximal enteritis. Vomiting in the horse thus often occurs with gastric rupture or terminally with shock. Stomach contents are usually pH 5 or below. Because it is a terminal event, vomiting in the horse is often grounds for rendering a poor prognosis. Abdominocentesis should be performed on a horse after vomiting to rule out gastric rupture. To avoid this sequence of events, decompression using a nasogastric tube should be performed in any horse with evidence of gastric distention (see approach to colic). Regurgitation and vomiting in horses

■ BOX 7.16

■ BOX 7.17

Causes of Regurgitation and Vomiting in Ruminants

Common Causes

Esophageal trauma or foreign body

Oral or pharyngeal foreign body, abscess, or trauma Salt toxicity (water deprivation/access)

Tumor, papilloma, or other mass in rumen or esophagus Toxins and poisonous plants

Less Common Causes

Megaesophagus

Hiatal or diaphragmatic hernia

Esophageal diverticulum

Esophageal reaction to Hypoderma Iineatum (B) Hydrocephalus

Meningitis, meningoencephalitis

Central nervous system trauma

Hypomagnesemia

Uncommon Causes

Intestinal neoplasia

Traumatic reticulitis

Tick paralysis

Tetanus

Bluetongue (O)

Peritonitis

Persistent right aortic arch

Pseudorabies

Rift Valley fever (exotic)

Toxins

Methanol or ethanol

Acute oral copper

Phosphorus Arsenic

Nitrates

Crude oil

Diesel fuel

Snake bite

Plant Toxins

Solanum species

Melia (chinaberry) Larkspur (Delphinium)

Cyanogenic plants

Nitrate accumulators

Death camas (Zigandenus species)

Castor bean

Oleander

Cocklebur

Tremorgenic toxins

Heath (Ericaceae)

Helenium (sneezeweed, bitterweed)

Hymenoxys (rubberweed, bitterweed) Veratrum (hellabore)

Amianthium (stagger grass) Haplopappus (burroweed) Psilostrophe (paper flowers) (O) Agrostemma githago (corn cockle) Kalmia (laurel)

Kikuyu grass, Pennisetum clandestinum (exotic)

Ibaraki disease (exotic)

Geigeria (exotic)

Yellow-wood (exotic)

B, Bovine; O, ovine.

Useful Techniques in Diagnosing Cause of Regurgitation

• Passing of stomach tube

• Endoscopy of pharynx, guttural pouches, esophagus, and stomach

• Ultrasound examination of the cervical esophagus may be helpful

• Radiographs; plain films of pharynx, guttural pouches, esophagus, and stomach

• Radiographs, barium swallows, checking gastric emptying time in horse

most commonly occur from the nose rather than into the mouth because of the anatomy of the soft palate.

In foals a few weeks to several months of age, milk returning from the nares is often associated with gastric ulceration, along with signs of colic, lying in dorsal recumbency, hypersalivation, and champing movements of the mouth. In advanced cases with duodenal ulcers, pyloric outflow can be obstructed by scarring, resulting in more pronounced signs. Foals 1 to 6 months of age are most susceptible to gastric ulceration.

Occasionally, neonatal foals without cleft palate have some mild degree of dysphagia with milk regurgitation from the nose for the first 24 to 48 hours of life, which spontaneously corrects. The cause of this is unknown, but it would appear to be a failure of normal swallowing events to be sufficiently strong or coordinated in the newborn. The major ruleout in these cases is cleft palate.

Approach to Diagnosis of Regurgitation and Vomiting

Evaluation of regurgitation or vomiting should include a history to determine possible exposure to toxins or poison plants, which is most likely when multiple animals are affected. Age of the animal limits some considerations; young animals are more prone to meningitis and central nervous system (CNS) trauma, and congenital problems such as esophageal diverticula and persistent right aortic arch are found only in neonates and may not manifest as choke or regurgitation until solid food intake is increased.

The physical examination can determine whether the problem is vomiting or regurgitation. In ruminants, regurgita­tion often occurs as a result of distention and overfilling of the rumen, resulting in an obviously distended abdomen. Painful pharyngeal lesions can also cause pharyngeal paresis, which results in gagging and regurgitating. In horses the most common causes of feed coming from the nares are spontaneous choke and pharyngeal paresis associated with guttural pouch lesions (see the dysphagia section later).

Physical examination should also include passing a stomach tube to determine whether any impediment to passage of ingesta is present (Box 7.17). Endoscopy is useful to visualize esophageal defects. Many endoscopes currently in use are not long enough to reach the stomach of the adult horse. Endoscopy of the rumen is rarely diagnostic because it is almost impossible to empty it adequately to allow for visualization of a lesion. Ultrasound of the cervical esophagus may also be useful.

In horses and small ruminants, radiography, particularly barium contrast studies, can be useful in detecting esophageal abnormalities. In foals, prolonged gastric emptying time may be diagnosed from contrast studies. Normal emptying and movement of contrast media into the small bowel occur in less than 2 hours; contrast media reach the large bowel by 3

hours. Radiography may also be useful in detecting diaphrag­matic hernia.

The most significant complications of regurgitation and vomiting include aspiration pneumonia, dehydration, and electrolyte imbalances. The marked hypochloremic alkalosis common to most monogastrics is rare in horses and occurs in ruminants mainly with internal vomiting (one type of vagal indigestion) associated with reflux of abomasal contents back into the rumen.

Vomiting, like diarrhea, is often an attempt by the body to rid itself of a noxious or toxic substance. Antiemetics are therefore rarely indicated in vomiting of central origin and rarely effective in regurgitation in large animals.