Loosie my horse was put to sleep because salmonella poisoning, the vet just wanted to treat her for colic (she was mildly gasy from it), and nothing else. I searched for another vet they ran tests for weeks (it wasn't showing up in the testing), until salmonella appeared in a fecal. At that put it killed her liver and working its way into her kidneys. The only symptom in the first two weeks was not eating hay, of course she dropped 400 pounds give or take in the 6 weeks, and other things. She was eating her grain though.