how old are these calves? Do there bums have a black matt look? How much blood is in the manure? It does sound like coccidiosis to me but never sure for a fact. Some people say it doesn't do anything, but try and give 120cc of peptobimol twice a day oraly, and revibe 2 twice a day oraly and depending on how much they weigh 3 1/2 cc of trivetrin once a day for 3 days, and the same with 1cc of banamine. That is what my vet recomended for me and it seemed to clear it up.