My guess would be an obstruction in the intestines but there are many reasons why this is could occur. I’ve obtained this information below from www.healthydogexperts.org/id13.html if you want to read more about it click on the link.
Constipation
Constipation means absent, infrequent, or difficult defecation. Most healthy dogs have one or two stools a day. This varies with the individual and the diet. A day or even two without stools is not a cause for concern, if the stools remain normal in size and pass without difficulty. But when feces are retained in the colon for two or three days, they become dry and hard and require forceful straining to pass. Note that straining also occurs in dogs with colitis, obstructed bladder and anorectal obstructions. It is important to be sure the dog is not suffering from one of these other problems before treating him for constipation. Colitis, in particular, is often confused with constipation. Remember that a dog with colitis will pass many small stools that contain mucus and/or blood.
Causes of Constipation
Many middle-aged and older dogs are prone to constipation. A common predisposing cause is failure to drink enough water. With mild dehydration, water is withdrawn from the colon, which dehydrates the feces. Ingesting foreign materials such as bone chips, hair, grass, cellulose, cloth, paper, and other substances is a well-recognized cause of acute and chronic constipation. The indigestible material mixes with feces to form rocklike masses in the colon. Many drugs commonly used in dogs cause constipation as a secondary side effect. Discuss this possible correlation with a trained professional. Hypothyroidism is an occasional cause of chronic constipation. The urge to defecate can also be voluntarily overridden. Dogs develop such inhibitions during housetraining. When left alone in the house for long periods, they often override the urge to defecate. Dogs may also be reluctant to empty their bowels when hospitalized, boarded, or taken on a trip. Dogs with constipation of recent onset should be examined by a trained professional. Other reasons to seek professional consultation are painful defecation, straining during defecation and passing blood or mucus.
Fecal Impaction
A fecal impaction is a mass of hard stool in the rectum and colon. There may be a predisposing condition, such as an enlarged prostate, that compresses the rectal canal. Dogs with fecal impactions pass little or no stool despite repeated and forceful straining attempts. Your dog can become lathargic, have no appetite, experience abdominal distension and vomiting and may have a hunched-up appearance. Digital rectum examination reveals a large tubular mass.
Diarrhea
Diarrhea is the passage of loose, unformed stools. In most cases there is a large volume of stool and an increased number of bowel movements. The two most common causes of diarrhea in dogs are dietary indiscretion and intestinal parasites. Many canine infectious diseases are also associated with acute diarrhea. Food takes about eight hours to pass through the small intestines. During that time, the bulk of the food and 80 percent of the water is absorbed. The colon concentrates the remainder. At the end, a well-formed stool is evacuated. A normal stool contains no mucus, blood or undigested food. With rapid transit through the bowel, food arrives at the rectum in a liquid state, resulting in a loose, unformed bowel movement. This type of rapid transit accounts for the majority of temporary diarrhea in dogs. Dietary indiscretion is a common cause of rapid transit. Dogs are natural scavengers and tend to eat many indigestible substances, including garbage and decayed food, dead animals, grass, wild and ornamental plants and pieces of plastic, wood, paper and other foreign materials. Many of these are irritating to the stomach as well as to the bowel, and are partially eliminated through vomiting. Food intolerance can also cause rapid transit. Foods that some dogs seem unable to tolerate can include beef, pork, chicken, horsemeat, fish, eggs, spices, corn, wheat, soy, gravies, salts, fats and commercial dog foods. Note that food intolerance is not the same as food allergy, which causes dermatitis and possibly vomiting, but rarely causes diarrhea. Some adult dogs are unable to digest milk and milk by-products because of a lactase deficiency. Lactase is an intestinal enzyme that breaks down the lactose in milk into small-chain sugars. Undigested lactose cannot be absorbed and remains in the bowel and holds water with it. This increases motility and causes large-volume diarrhea.
Discussions: constipation and diarrhea
