Causes of Canine Gastrointestinal Obstructions
Some basic canine anatomy can be quite helpful when trying to get a feel for the causes and consequences of gastrointestinal obstructions in domestic dogs. Solid food, fluids and other ingested items enter a dog’s digestive tract through its mouth. The processes of chewing, together with the secretion of saliva from the salivary glands into the mouth, are the first mechanisms that physically start breaking food down into digestible pieces. After the dog swallows whatever it has taken into its mouth , the material passes over its tongue, through its throat, down its esophagus and into its stomach where gastric acid and other secretions help to further break down food into more absorbable pieces. Eventually, if things are working properly, the ingesta – the swallowed food - moves out of the stomach into the small intestine, where most of the absorption of nutrients occurs. Reabsorption of water primarily takes place in the large intestine. Finally, formed feces pass through the rectum and out the anus.
The outlet portal from the stomach to the small intestine is called the “pylorus,” or the “pyloric canal.” The pylorus is smaller in diameter than the inlet into the stomach from the tube-like esophagus. It is this anatomical feature that makes it possible for a dog to swallow something quite large, which can get into but not out of its stomach. The pylorus is surrounded by a strong band of circular muscle, which helps to manage the movement of materials out of the stomach into the next part of the digestive tract. When things work as they are supposed to, the contents of the stomach are emptied through the pylorus into the duodenum, which is the first section of the small intestine. The other two parts of the small intestine are the jejunum and the ileum, in that order. The small intestine ends at the beginning of the large intestine. The large intestine is comprised of the cecum, colon, rectum and anal canal. Most of the fluid part of the ingesta is absorbed in the large intestine as undigestible material passes through on its way to the rectum, and then out through the anus as formed feces.
Gastric Outflow Obstruction
Gastric outflow obstructions are fairly common in domestic dogs. They can be caused by almost anything that becomes stuck in the stomach or in the pyloric canal. Sticks, rocks, needles, pins, thermometers, bones, toothpicks, rawhides, stuffed animals, tennis balls, shreds of fabric and other assorted foreign objects have all been the causes of complete or partial gastric outflow obstructions in companion dogs. Tumors, masses or other abnormal growths, and gastric dilatation and volvulus (GDV; bloat; torsion), can also block the pyloric opening, as can scarring of the stomach lining and pyloric tissues from gastritis, gastroenteritis, gastric ulcers or other causes. Other things that may prevent ingesta from leaving the stomach are chronic hypertrophic pyloric gastropathy (CHPG) and congenital pyloric stenosis, which is a narrowing of the pylorus that is present at birth.
Small Intestinal Obstruction
Obstructions of the small intestine are also fairly common in companion dogs. These can be caused by many things, including hernias, intussusception, twisting of the mesentery and intestinal tissues, masses, intestinal strictures, gastritis, gastroenteritis and lodged foreign bodies. An “intussusception” is the prolapse of one part of the intestine into the lumen (open center part) of an adjacent part of the intestine. This is much like what happens when one part of a tube sock is pushed into another part of the same sock, like when it is partially turned inside-out. Of course, when this happens to the intestines, it is a medical emergency, because injesta become completely blocked from passing through. A “hernia” is the abnormal protrusion of part of an organ or tissue through some surrounding structure. A layperson’s term for a hernia is a “rupture” of some tissue that permits some other tissue to pass through the rupture opening. The “mesentery” is a membranous sheet that attaches various abdominal organs to the belly wall; the intestines are attached by mesentery to the upper wall of the abdominal cavity. A “stricture” is an abnormal narrowing of a duct or tubular organ, such as the intestines or esophagus. “Gastritis” and “gastroenteritis” refer to inflammation of the stomach or the stomach and intestines. Gastrointestinal parasites, especially roundworms in young puppies, can cause intestinal intussusceptions and gastroenteritis that often contribute to GI obstructions.
Prevention of Gastrointestinal Obstruction
There is no fool-proof way to prevent gastrointestinal blockages from occurring in domestic dogs. Owners should keep their dogs from chewing on sharp, large or long foreign objects that they could accidentally or intentionally swallow, such as shredded rugs or fabric, sticks, stones, bones, small toys, fruit pits (peaches, plums, etc.), balls, strings and similar items. Many long-time dog owners and veterinarians recommend not feeding dogs rawhides, pig ears, cow hooves or other pressed, rolled, basted or baked chew products, unless the dogs are closely supervised while they are gnawing on their treats. It is no mystery that dogs can be indiscriminate eaters. “Dietary indiscretion” is a veterinary term for when a dog has eaten something that it obviously shouldn’t, like aluminum can, toothbrush, shoelace or shoe. Another, less polite phrase for this type of activity is “garbage gut.” Dog owners should keep their pets away from outdoor trash cans and should be sure that indoor waste receptacles are well-secured – especially in the kitchen.
Bones and rawhides are among the most common causes of gastrointestinal obstructions in companion dogs. Cooked bones, such as beef marrow or knuckle bones from the femur, are more likely to chip or break off sharp pieces than are raw bones, although both can become stuck in and even puncture the stomach or small intestine. Chicken and turkey drumsticks are notorious for splintering and, because they are so sharp, causing gastrointestinal perforation. Dogs that voluntarily eat foreign objects are likely to be repeat offenders. Owners must be diligent about keeping their pets away from bones, stones, sticks, needles, pins, pieces of fabric, children’s toys and other possible items that could lodge in their stomach or intestines and cause a potentially life-threatening blockage.