Diarrhea and weight loss in dogs can be caused by a number of conditions involving the intestines. You should contact your veterinarian immediately if your dog has bloody diarrhea or if it is black or tarry; if you think he may have eaten something poisonous; if he is depressed or has a fever; if his gums are yellow or pale; if he is a puppy or is not up-to-date on his vaccinations; if he exhibits signs of pain; or if he is vomiting along with the diarrhea.
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Intestinal Parasites
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Roundworms are intestinal parasites that can cause diarrhea, weight loss and slow growth in puppies. They are diagnosed by a fecal flotation test. Treatment includes de-worming medicine (sometimes multiple treatments) and decontamination of the environment (such as bedding and toys). Giardia is another intestinal parasite that causes diarrhea and weight loss. It usually appears in young dogs or dogs with a suppressed immune system. Treatment includes medications, bathing and decontamination of the environment.
Bacterial Overgrowth
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Bacterial overgrowth can occur in the small intestines of dogs with existing intestinal disorders such as exocrine pancreatic insufficiency or inflammatory bowel disease, and frequently occurs in German shepherds. It is diagnosed with fecal and blood tests, ultrasound, and in some cases, intestinal biopsy. Treatment includes a 4 to 6 week course of antibiotics and a low fat, low carbohydrate diet.
Lymphangiectasia
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Lymphangiectasia is the dilation of the lymphatic vessels due to congenital defects. It can also result in congestive heart failure, inflammatory bowel disease or cancer. It is diagnosed through endoscopic biopsy or exploratory surgery. Treatment can include a low fat diet, glucocorticoids, B12 injections and treatment of the underlying condition. There is no cure and the prognosis is not good for this illness.
Tumors
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Tumors such as lymphoma and adenocarcinoma can cause chronic diarrhea and weight loss in dogs. These tumors occur primarily in middle-aged to older dogs. Diagnosis is made through physical exam and intestinal biopsy. Treatment includes surgery and/or chemotherapy.
Exocrine Pancreatic Insufficiency
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Exocrine pancreatic insufficiency is a problem with the digestion and absorption of nutrients. It occurs most frequently in dogs with a history of pancreatitis, rough coated Collies and young German shepherds. It is diagnosed with a blood test. Treatment can include antibiotics to inhibit bacterial overgrowth, pancreatic enzyme replacement therapy and in some cases a change in diet to include easily digested foods. Vitamin supplements may also be given. According to Pet Education, pancreatic enzyme replacement therapy can be very costly at $60 to $100 a month.
Inflammatory Bowel Disease
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Inflammatory bowel disease such as granulomatous enteritis or eosinophilic gastroenterocolitis can occur in middle-aged dogs and is common in German shepherds and Basenjis with lymphocytic plasmacytic enteritis. Enteritis is an inflammation of the small bowel and this condition usually results from problems with the immune system. Diagnosis is made with fecal tests and intestinal biopsies. Treatment includes a modified diet with a restriction of fat, antibiotics such as metronidazole (Flagyl), immunosuppressants such as prednisone and anti-inflammatory medications.
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