Diseases of the Digestive System

Chapter 49 Diseases of the Digestive System



NORMAL DIGESTIVE SYSTEM ANATOMY


The digestive tract of the horse is that of an animal that was designed for grazing—that is, constant walking and eating. The lips of the horse, designed for prehension of grass, are amazingly sensitive and can sift out powdered medication when it is mixed in with their feed.


The horse’s teeth are that of an animal adapted for grazing. The teeth have enamel ridges that traverse the chewing surfaces and are constantly erupting throughout the horse’s life. As some of the enamel ridges get worn away, they are replaced by the ever-growing tooth. This constant tooth eruption, as well as the fact that the horse’s upper jaw is wider than its lower jaw, can lead to dental concerns as the horse goes through life.


The horse’s esophagus is a long, muscular tube that courses from the animal’s mouth to the stomach. The esophagus is mainly made up of two layers of smooth muscle: an inner circular layer and a longitudinal outer layer. These two layers of smooth muscle, and the way they work in concert, allow a horse to swallow its food.


The stomach of a horse is relatively small in comparison with its body size. The stomach of the average 1,100-pound horse has the same capacity of a 250-pound hog—roughly 2 to 4 gallons. There are two regions to the stomach: a nonglandular portion takes up roughly the proximal half, and the distal half is glandular. The small size of the stomach and its constant secretion of HCl have an impact on the horse’s feeding schedule, of which the owners need to be aware. The main function of the stomach is mixing of the feed with digestive juices and the start of protein digestion. The stomach also absorbs small amounts of water, alcohols, and water-soluble medications.


The small intestine is where most of the digestion and absorption of the concentrate portion of the feed occurs. Foodstuffs are broken down by chemical digestion mainly in the duodenum, which is the portion closest to the stomach. The resultant materials are absorbed as they pass through the jejunum and the ileum.


The fibrous portion of the diet empties from the ileum into the cecum. The cecum is a large, comma-shaped organ that comprises much of the right side of the horse’s abdominal cavity. The main function of the cecum is fiber digestion. Here, the microorganisms break down the fiber portion of the diet into glucose and volatile fatty acids (VFAs). The glucose is used by the gut microorganisms, and the VFAs are used by the horse for energy.


After digestion by the cecum, the remaining material goes into the large colon. The large colon has four portions: the right and left ventral and dorsal colons. The contents then travel into the transverse and then the descending colons. The main function of the colon is to absorb water from the feedstuff.


Many of the digestive system diseases that are seen in horses can be attributed to their somewhat peculiar digestive anatomy.



DENTAL CONSIDERATIONS: UNEVEN TOOTH WEAR


Because of the modification of diet and feeding patterns by domestication, demands on young performance horses, and the lack of selection for dental soundness, most horses need regular dental evaluation and work. Regular dental work can improve the horse’s comfort, increase efficiency of feed utilization, and possibly increase its performance.


As stated earlier, the horse’s teeth are constantly erupting throughout its life, and its upper jaw is wider than the lower jaw. This can lead to an uneven wear pattern of the occlusal surfaces of the teeth.


Common dental abnormalities that need attention include (Fig. 49-1):


• Sharp enamel points on the lingual and buccal surfaces

• Sharp hooks that protrude downward from the first or last tooth of the upper arcade

• Sharp ramps that protrude upward from the first or last tooth of the lower arcade

• Wave mouth

• Step mouth that results from a lack of wear of one tooth, allowing it to grow excessively long

• Retained wolf teeth that can cause pain to the tongue when it is displaced because of bit pressure

image image image

Figure 49-1 A, Normal mouth before dentistry. B, Normal mouth after dentistry. C, Lateral view of upper 6 hooks, lower 11 ramps.


(From Allen T: Manual of equine dentistry, St Louis, 2003, Mosby, by permission.)




CLINICAL SIGNS



• Bit avoidance

• Quidding (dropping small, chewed bits of hay)

• Poor performance

• Undigested feed in feces

• Weight loss

• Prolonged eating time


TREATMENT



• If the veterinarian sees any of the above problems on a dental examination, he or she should take steps to correct the problem.

• Hooks, ramps, sharp points, and wave mouths can be corrected by floating the horse’s teeth. Basically, a rasp is passed over the tooth to remove the unwanted sharp portions. Floats can be either hand floats or power floats. Power floats are becoming more commonly used because they are easier on the user.


INFORMATION FOR CLIENTS



• Yearly dental examinations should be performed on every horse. Older horses may need twice yearly floating to maintain dental health.

• Weight loss and loss of condition may be a sign of dental problems.



TECH ALERT


Use of a proper mouth gag is important to get a complete examination of the dental arcade. Avoid placing fingers between the teeth when not using a mouth gag. Use of the tongue as a mouth gag can damage the tongue and should be avoided.



CHOKE


Choke refers to a condition where a partial or total obstruction of the esophagus occurs, usually caused by feed impaction. Horses that choke often have a history of bolting their feed. Choke may also occur if a horse is fed too quickly after sedation. There are numerous potential causes for the esophagus to become obstructed. Causes of choke may include:


• Feed (oftentimes pelleted feeds) expansion when it hits esophagus

• Drugs that cause decrease in smooth muscle motility
Xylazine (Rompun)

Detomidine (Dormosedan)

• Trauma, inflammation

• Scar tissue

• Neoplasia



CLINICAL SIGNS



• Difficulty swallowing

• Excessive salivation

• Swelling of throat

• Discharge of food from nostrils

• Neck extension


DIFFERENTIAL DIAGNOSES



• The following conditions should also be considered if a horse is showing clinical signs of choke
Dysphagia due to nerve deficits

Cleft palate

Dental problems

Oral foreign body


DIAGNOSIS



• Definitive diagnosis can be obtained by palpation of the esophagus and passage of nasogastric (NG) tube (or lack thereof).

• The veterinarian may also elect to perform radiographs to visually localize the obstruction.


TREATMENT



• Relax the horse, especially the smooth muscles (Rompun, Dormosedan, lidocaine through tube)

• Lavage with gallons of warm water through NG tube

• Esophageal massage

• Intravenous (IV) fluid therapy

• Severe cases may need general anesthesia

• Antibiotics to combat secondary aspiration pneumonia

• Nonsteroidal antiinflammatory drugs (NSAIDs) to reduce esophageal inflammation


INFORMATION FOR CLIENTS



• Do not allow access to feed/hay for 4 hours after sedation.

• If feeding dry feeds that will expand, make sure that the animal consumes them slowly, or soak them first.

• When feeding apples, carrots, or other bulky items, cut them in smaller pieces to avoid the horse swallowing them whole.



TECH ALERT


Signs of choke may be mild to severe. Get a good history and palpate the entire length of the esophagus.



GASTRIC ULCERS


Gastric ulcers have become a much more frequently recognized disease in recent years. It is estimated that greater than 80% of show and race horses have some degree of mucosal ulceration.


The prevalence of gastric ulcers in horses is mainly due to management techniques. Most heavily worked horses are kept in stalls for 22 or more hours each day. They are fed high-concentrate meals rather than being allowed to graze freely all day. Feeding concentrate meals predisposes a horse to ulcers by two major pathways:


1. Lack of saliva production

2. Constant secretion of hydrochloric acid in the stomach

Saliva contains bicarbonate and acts as a natural buffer to the stomach acids. A horse can salivate only when it has something in its mouth. A grazing horse is salivating nearly constantly, whereas one fed in meals salivates only at mealtime. A grazing horse also has a constant physical buffer in the stomach to protect it from the acid environment. Concentrate feeds also contribute to the problem because concentrates produce one-fourth the amount of saliva when compared with an equal amount of forages.


NSAIDs such as flunixin meglumine and phenylbutazone have been shown to cause ulcers in the stomach and other portions of the digestive tract, especially in the right dorsal colon. If possible, the use of NSAIDs should be limited to 5 to 7 days. Oral NSAIDs should also be administered with a meal.




CLINICAL SIGNS



• Chronic, low-grade colic (see later)

• Anemia may be present if gastric ulcers are severe and chronic

• Loss of condition and decreased endurance


DIAGNOSIS



• Gastric ulcers are diagnosed by an endoscopic examination of the stomach


TREATMENT



• Treatment of gastric ulcers includes medication and management changes.

• Omeprazole has been found to be the most effective pharmaceutical agent for the treatment of gastric ulcers.

• Management changes that may help the problem are letting the horse out to graze for as many hours as possible during the day; feeding small, frequent meals; and increasing the amount of forage whereas decreasing the amount of concentrate consumed.


INFORMATION FOR CLIENTS



• Performance horses, young horses in training, and stalled horses are most at risk for development of ulcers. Make sure your training program gives the animal plenty of relaxation time, more forage in the diet, and lots of grazing. If you suspect problems, have an endoscopic examination. Ulcers can be healed before they cause problems.

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Aug 31, 2016 | Posted by in GENERAL | Comments Off on Diseases of the Digestive System

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