Hi Terry, Was your puppy on any antibiotics post surgery? Normally they are not given but occasional one hears of a vet giving them. Also post surgery can cause some patients to have nausea and diarrhea and it is necessary to rest the stomach and feed small helpings of boiled lean hamburger and equal measure of overcooked cheap starchy rice (not the converted type like Uncle Ben's). Also give some probiotics like lactobacillus acidophilus which you can buy in capsule form from the health food store or pharmacy. Do not feed yoghurt at this time as the dairy fat might aggravate the condition especially if full fat.
Are you absolutely sure puppy has not eaten any item of clothing or string like material. Rose T.
