Many health problems in dogs are seasonal in nature. Spring brings skin problems; winter plays havoc with arthritic joints. Summer is the season for colitis and diarrhea. Common causes range from getting too much liver at a dog show, being stressed by thunderstorms, heat, and fireworks, or eating “something” outdoors. Symptoms include straining to defecate, production of scant or copious amounts of watery feces that may contain mucus and/or blood, and increased urgency to defecate. While usually not life threatening, we of course want to resolve these cases quickly, for the benefit of both dog and owner.

Inflammation of the colon, termed colitis, is often the underlying reason for diarrhea. The colon is the very last portion of gastrointestinal tract, where the waste products of digestion are formed into stool, and water is reabsorbed. The innermost lining of the colon, called the mucosa, as the name suggests, has numerous mucus glands that protect the colon from injury and lubricate the passage of feces. Inflammation interferes with mucus production and adherence, and the colon lining becomes fragile and ineffective at water absorption. As water is not effectively reabsorbed, large amounts of watery diarrhea are produced. Excessive amounts of mucus, and even blood, are often passed with the feces of dogs affected with colitis because of damage to the protective mucosa lining. While this is not a cause for panic as long as your dog is acting normally, dogs with bleeding should be examined by their veterinarian. If your dog is lethargic, weak, or showing other signs, seek care immediately.

Inflammation in the colon also impairs effective contractions and movement of the colon. The colon normally moves the feces slowly back and forth, enabling maximum absorption of fluids. When these contractions are ineffective, the contents pass too quickly through the colon and diarrhea ensues, as water is not reabsorbed. As the dog strains to contract the colon, the fragile lining of the colon is further stressed, and additional bleeding can occur.

Determining the cause of the diarrhea may be straightforward, such as in the case of the dog that ate the plate of deviled eggs at the cookout. Parasites such as whipworms or Giardia can also cause diarrhea and colitis. While dogs on monthly heartworm preventative are less likely to have intestinal worms, Giardia, a one-celled parasite, is becoming a more common cause on non-specific colitis and intermittent diarrhea. Dietary changes or changes in routine may also play a role in sensitive dogs. In some cases we are unable to firmly establish a cause; however, symptomatic treatment usually provides quick relief.

Certain bacteria can also cause colitis. These bacteria normally live in the colon but, when conditions are right, these bacteria overgrow, and colitis develops. A species of bacteria called Clostridium perfringens is an extremely common cause of colitis in dogs. C. perfringens causes inflammation of the colon by producing a toxic substance called an enterotoxin. This toxin acts directly on the colon mucosa, causes the escape of fluid and salts (also called electrolytes), and results in decreased movement, which produces diarrhea.

The treatment of colitis is aimed at decreasing inflammation and treating any bacterial or parasitic infection. A bland diet or home-prepared food is often used in the management of colitis, with a gradual change back to the regular diet. A mixture of one quarter boiled meat (usually chicken) and three quarters brown rice is a common bland meal for a dog with diarrhea. Ideally, skip a meal before starting a bland diet plan. Feed about half the amount of your dog’s usual meal size. Begin to mix in the regular food when the diarrhea stops, gradually returning to the regular diet.
Many owners prefer the “Potato Meal” to a rice based meal. This mixture (recipe below) of white potatoes, sweet potatoes, turnips, and leek, provides readily digested carbohydrates, fiber, and virtually no fats. Feed a slightly smaller amount than your dog's regular diet. Feed as the only solid food until the diarrhea stops, and then mix with your dog's regular food for one to two days before a gradual return to your dog’s regular diet.

Various medications may be used to control infectious or parasitic diarrheas. Metronidazole, or Flagyl® is one of the most commonly used medications. It is effective against Giardia, as well as general bacterial overgrowth in the colon. It is often effective in just one or two doses; however it should be continued for 4-5 days to be sure of adequate control of bacterial populations.

Natural products such as probiotic blends provide beneficial bacteria and compounds that support the healing of intestinal cells. Those who feed a natural diet often add a probiotic supplement to meals. Probiotics are often prescribed in conjunction with antibiotic therapy for other diseases, where disruption of normal bacterial flora in the colon is likely. By supporting the natural population of bacteria in the colon on a daily basis, disruption of the normal bacterial population is less likely.

For most dogs, colitis will not be a common occurrence. A few dogs will have more chronic forms, usually associated with food intolerance or allergy, or immune complex deposition, such as lymphocytic or plasmocytic enteritis. It should be noted that some serious health issues can first present as colitis, such as parvovirus, intestinal cancers, pancreatitis, Lyme disease, or blood clotting disorders. For this reason, it is always wise to consult your veterinarian if diarrhea is persistent, contains blood, or if your dog shows additional symptoms beyond diarrhea.

While usually not life threatening, diarrhea can quickly weaken puppies or dogs with pre-existing health problems. It is wise to seek veterinary care immediately in these cases. Fortunately, the vast majority of dogs with colitis are back to normal in just a few days. Those with frequent episodes or those that don’t respond to symptomatic treatment should be fully evaluated for an underlying cause. With appropriate diet, medications, and supplements, many of these cases can be successfully managed.

The Potato Meal
This home cooked meal is an alternative to the traditional chicken and rice often recommended for dogs with diarrhea. It is ideal for dogs on a grain-free diet. For short term use only.

3 white potatoes, cut in chunks
3 sweet potatoes, cut in chunks (of similar size to the white potatoes)
1 turnip, cut in slices
1 leek, cut in slices, including the green portion (rinse well before cutting)
Boil all vegetables until softened, stirring often. Add a small amount of boiled meat (chicken, turkey, beef) for flavor at the time of serving. Feed slightly less than your dog’s normal meal portion. Feed until the diarrhea resolves, then mix with your dog’s regular diet for a gradual transition back to his usual food.