We switched our lab's food about a month ago from purina one to purina dog chow. we noticed he was throwing it up a couple of weeks ago and thought it was due to overeating too fast. we took him to the vet after several tries to slow his eating and xrays showed he was blocked up with food from his rectum to his stomach. it wasn't digesting. the vet gave him some anti vomiting pills that didn't work for him. we were sent to an internal medicine vet for an ultrasound. that showed no obvious obstruction. blood work all came back normal with no disease. we went to our previous vet for an enema. little bits of feces did come out, but they were really small. he didn't get the diarrhea that was expected from the enema last night. the vet did say that constipation could cause vomiting. our lab vomited last night for a while and then was able to keep down water for the rest of the night. this morning i gave him an antacid (recommended by the vet) and he kept that down, some food, and his water. he still has yet to pass a bowel movement. i wonder if we should to the recommeded endoscopy (a PRICEY procedure.. we've already spent $800 we don't have).. or if it is safe to wait a bit longer to see if he can pass his stool on his own. anyone ever deal with this? any suggestions? our lab is only four and was fine before we started feeding him the cheaper brand of food.. please help!