The horses digestive system and colic

The types of colic and how to recognize themColic is a descriptive term referring to abdominal pain of any type. It is not a specific disease, as many trainers would believe, but rather a vague term that refers to a broad category of conditions that can result in a painful belly.
Horses cannot tolerate this gut pain if it persists, and can react violently by stomping their feet, thrashing their heads on the ground, and rolling from side to side. In many cases of colic, these secondary reactions to the pain can result in more severe damage to the horse than the colic itself. Thus, it is very important to have an understanding of the digestive tract, the different types of colic that can affect the horse, and how to recognize this condition early, minimizing the risks associated with this common equine affliction.

The digestive system
This system consists of those organs involving the intake and digestion of food, and the expulsion of the unused portion. The digestive tract of the horse contains the stomach, the three sections of the small intestinethe duodenum, jejunum, and ileumand the large intestine, which consists of the cecum (appendix) and colon.
The stomach of the horse is very small (2-to-3 gallons) and accounts for very little absorption of nutrients. Its main function is to transmit the ingesta to the remainder of the digestive tract. Food enters and passes through the stomach very rapidly. Vomiting is very uncommon in the horse and it is considered a very grave sign when it occurs. This is because the vomiting center of the brain and the corresponding innervation to the stomach is very poorly developed in the horse.
The small intestine is another relatively small area of the digestive tract, and holds about 45-to-55 gallons and is about 70 feet in length. This is where most of the fluid is absorbed to aid in digestion and absorption of the various proteins and soluble carbohydrates.
The horse is regarded as having the ultimate in large intestine function. The large intestine is approximately 25 feet long and can hold up to 55 gallons. The bacteria and protozoa that live within this organ work to process and break down the plant material by fermenting it into fatty acids and carbohydrates for usable energy and body maintenance. Water storage and reabsorption are other important functions of the large intestine.
For a 1,000-pound horse, the contents of the entire digestive tract can account for approximately 250 pounds. Thus, when a horse goes off his feed, inadequate consumption of food and water causes the animal to lose weight and dehydrate. Over just a few days, any horse can easily drop 100 pounds in lost nutrients and fluids, giving him that tucked-up appearance.
The abdominal cavity of the horse is lined with a smooth, thin, serous-like membrane called the peritoneum. This membrane serves to coat the abdominal area with a smooth frictionless surface, allowing the intestines to move around freely. However, this membrane is very delicate, and can easily become inflamed when abdominal complications or disease occurs. Inflammation of the peritoneum is called peritonitis.
Circulation to the digestive tract is supplied by arteries and veins. However, one main artery, the anterior mesenteric artery, is responsible for the majority of the circulation to the digestive tract. If the ability of this vessel to pass blood becomes compromised, it limits the necessary blood supply to the digestive organs. Poor blood flow to areas of the intestines can cause them to become weakened, inflamed, and possibly to rupture, spilling intestinal contents throughout the abdominal cavity. This initiates a very serious condition called peritonitis that was previously described.

Types of colic
For simplicity, colic can be classified in the manner in which it affects the digestive tract. There are three main forms:

• 1) Obstruction and/or distention of the digestive tract, as in impaction or constipation colic.
  
• 2) A loss of blood supply, or ischemia, to the organs of the digestive tract, as in a parasitic condition.
  
• 3) A tension or pulling on the intestines if they become twisted, trapped, or malpositioned within the abdominal cavity.
  

Distention and/or impaction colic can occur in several ways. Eating too much grain or very succulent grass can result in excessive gas production. This, in turn, can cause a distention and stretching of the intestines, with the horse becoming very uncomfortable and taking on a bloated appearance. These animals will tend to pass large amounts of gas and you generally can hear the gurgling sounds of their intestines as they look to their side for relief. Treatment consists of relieving the pain and gas production.
The reverse of this condition is when the horse becomes constipated over several days and gradually becomes uncomfortable and unable to pass feces. These animals tend to become increasingly depressed and have irregular, picky appetites. Initially, these animals do not experience pain. However, as the disease condition progresses and the impaction worsens, severe pain will be observed. These impactions can occur anywhere in the digestive tract, but commonly occur at areas where the intestines bend and their openings narrow. Treatment consists of fluids and mineral oil to rehydrate the animal and relieve the constipation.
Foreign bodies such as rope, fence materials, and plastics can combine to form enteroliths within the intestinal tract, and in rare cases intestinal and abdominal tumors may be associated with colic and the obstruction of various portions of the intestinal tract.
Parasitism is the most common cause of ischemia, or loss of blood supply, to a specific area of the intestines. As the parasites move within the intestines and their larval forms migrate through the intestinal walls and into the blood vessels, the circulation can be compromised or lost. These colics can start insidiously, where the animal may be stricken with minor bouts of pain that resolve on their own. Over time, these colic cases become more frequent and more severe as the damage progresses. Eventually, the affected blood vessel or vessels become completely occluded and the intestinal area supplied by these vessels becomes swollen and inflamed and will rupture, like an appendix. These conditions are serious and in most cases fatal. Treatment for these conditions is preventative by combining good stable management with a proper parasite control program.
Pulling or tension colic can occur in several ways. If a horse is allowed to kick and roll from side to side when he first experiences colic pain, these hypermotile, sensitive, gaseous intestines can move between and around each other becoming twisted like a balloon. If this twisting persists, the intestines can become occluded, losing their patency and blood supply. This, in turn, sets up an inflammatory process that is extremely painful to the horse, causing him to sweat profusely, become very shocky, and possibly collapse, with pain medications providing little relief. These inflamed intestines can also rupture, allowing intestinal contents to contaminate the abdominal cavity, further complicating this disease condition.

Signs to look for
For a trainer or a person to recognize the sick horse, one must fully understand the behavioral characteristics and physical dimensions of the healthy horse. There should be a set routine where one enters the stable and observes each individual animal for physical appearance, attitude, appetite, and normal bowel and urination habits. If any of these characteristics appear to be abnormal, the animal should be more closely examined. This examination should include the standard temperature, respiratory, and pulse rates. Normal values for the horse are:

• Temperature99.5-to-101.2 Fahr.
  
• Pulse28-to-40 beats/min.
  
• Respiratory rate15-to-20/min.
  

If any of these parameters are abnormal, a more complete physical examination should be performed.
As horses experience pain, such as that expected in colic conditions, the pulse and respiratory rates are good indicators of the severity of that pain. Increased respiratory and pulse rates are signs that the condition is becoming serious and veterinary attention may be required. Sweating is another indicator of severe animal pain and a worsening disease condition. An increase in body temperature during colic can be an indication of intestinal infection and inflammation.
Whenever colic strikes your stable, it is very important to determine the type of colic, its possible severity, and to carefully observe its progression. Early treatment and the physical parameters of your horse will determine the course of the specific colic. Fortunately, most colic cases are mild and can be treated successfully. However, the astute horseperson that properly assesses colic situations will greatly improve the outcome of those more serious and often fatal cases.
One morning, I was rushing to complete a lameness exam on a trainers horse when he asked, Whats your hurry, Doc? I quickly replied that another trainer had called about a horse that wouldnt eat and did not move his bowels and wanted me to examine him as soon as I could. As I left the stable to examine this horse, the trainer said, If he doesnt want that horse, Ill take him. I have been looking for a horse like that for years!

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Douglas B. Hutchins, MS, DVM, is a veterinarian in the Professional Services Department of Fort Dodge Laboratories.