Colon or Rectum Disorder
When there is a problem occurring inside the colon or the rectum, your dog will experience pain when they try to defecate. Masses, such as cancer or polyps, can cause the fecal matter to back up and be more difficult for your dog to pass. This can cause them to yelp when they defecate. Dogs that have swallowed small foreign objects may pass them through the colon and rectum and then out of the body. This can cause pain if the foreign object is irregularly shaped or has jagged edges. Strictures or narrowing of the colon or rectum can make it difficult for your dog to pass feces out of the body.
Mass on the Anus or Perineum
Masses such as cancer or polyps on the anus or the perineum can cause your dog to yelp when he defecates. The anus can also have a stricture or narrowing that makes it more difficult for your dog to pass fecal matter out of the body. Anal gland infections, abscesses or cancer can cause pain when defecating. Sometimes your dog may suffer from a perineal hernia. A perineal hernia is when the tissue within the pelvis and into the soft tissue behind the hip becomes herniated. This can cause pain when your dog attempts to defecate. Another possible condition that your dog may be suffering from is perineal fistula. This occurs when the skin around the anus becomes infected and ulcerated.
Constipation
When your dog is constipated and straining to defecate, it can become painful for them. If you notice they are straining excessively and producing very little, if any, feces they may be constipated. Dogs that are suffering from constipation might respond to over the counter medications, but you should also consult with your veterinarian before giving any medications to your dog.
Pseudocoprostasis
Keeping your dog’s hind end well groomed and in some instances, clipped short is not just to make them look good. When there are knots or mats around the anus, feces can become trapped and cause pseudocoprostasis. With feces trapped so close to the skin an infection can occur. In severe cases, the hair is so matted that feces are unable to escape the body and begin to back up into the colon, making your dog severely sick.
Prostate Problems
For male dogs, the colon is located above the prostate gland. When there is a problem with the prostate gland, such as an infection, cancer or abscess, it can cause your dog to experience pain when they try to defecate.
Mass or Injury in the Pelvic Region
Fractures or injuries to the pelvic bones can cause your dog pain when they have to strain to defecate. Masses or infections can also cause your dog to feel pain when they attempt to defecate.