There are a lot of potential reasons why your dog might be constipated, ranging from non-serious to possibly life threatening. Constipation can be the result of some sort of blockage inside the colon, an obstruction outside of the colon, or a disease or injury to a nerve.
Fecal matter normally moves smoothly through dog’s system into the colon, where electrolytes and water are taken out to be used elsewhere in the body. A process known as peristalsis moves feces through the colon and through the anus. However, if something either slows or impairs this process, the fecal matter will stay in the colon. It will continue to dry and harden until it becomes impossible for the dog to defecate.
Diet is usually the main culprit behind canine constipation. Dogs are much the same as humans in that if they don’t get enough fiber they can sometimes have difficulty defecating. And, of course, dogs will eat just about anything they can get to, whether that’s your Sunday dinner or a toy. Many of them, for whatever reason, also like to get into a cat’s litter box and eat whatever they can find. Calcium in the diet, such as bone meal, dog bones and other sources, can also make it difficult for a dog to “go.”
Older dogs are often at a higher risk for becoming constipated, as can dogs who don’t get out and exercise as much as they need.