Your dog may be lacking something nutritionally or may not be getting enough to eat. The dog may also be doing it out of boredom, loneliness, anxiety or stress.
This occurs for the same reason that dogs sometimes eat dog poop. The symption is called coprophagia. Some of the causes include a nutritional deficiency, learned behavior from observing other animals, or extreme hunger.
Actually this is a common habit in all canines, their eating of bowels (or poop) is not limited to Cat poop. You should train your Dog not to do that, as it's the only way to stop the habit.
