Constipation can be caused by a lot of different things in pets such as diet, drugs, stressful events/change in environment, trauma, foreign bodies, and/or masses or defects in the colon or rectum. If you have not seen your pet pass feces in more than 48 hours, seek veterinary attention. The longer waste sits in the digestive system the more water will be pulled out and making it even harder and more difficult to pass. This can lead to nerve and muscle damage. A veterinarian must examine your pet to rule out potential causes and decide the appropriate course of treatment.