Other reasons for a delay in pooping after surgery has to do with anesthesia, which slows gastrointestinal motility. Medications can interfere with dogs being able to poop. Some drugs decrease transit time, which is how long it takes for food to make its way from the mouth all the way through the GI tract. Meds like antibiotics are important for destroying bacteria, but they also reduce the healthy gut flora that keeps stools at the right consistency, so constipation may occur but diarrhea can too (Don't use this as a reason to change the way you give veterinary prescribed antibiotic. Always consult with your veterinarian if you have medication concerns). Last, certain meds cause stomach upset. When our dogs' bellies aren't feeling right, they might eat less. The combination may delay normal bowel movements.