"Rebel," a 13 year old quarter horse gelding, presented to the Large Animal Clinic at Cornell University in mid-June for a four day history of icterus, change in attitude and lethargy. Rebel was kept on a 4 acre pasture with two other horses on which they spent the majority of the day. They were brought in at night and given a small amount of hay and grain to supplement what they ate while out on pasture. One of these horses, a 28 yr old gelding, had what the owners described as an "episode of jaundice" 2-3 months earlier that resolved with treatment with sulfamethadiazines and fluid therapy by the referring DVM. The other horse, Rebel's half brother, JR, had been euthanized by the referring DVM the morning of Rebel's presentation to the LAC. Approximately ten days earlier, JR started acting unusual and wanted to stay inside, specifically in the darkest corner of his stall. A day or two later, he was noticed to be icteric. JR quickly progressed from lethargy and depression, to ataxia, seizuring and head pressing. He was euthanized about one week after the onset of icterus. Abbreviated bloodwork from the referring DVM showed signs of dehydration (elevated hematocrit and total protein), a possible inflammatory process (neutrophilia) and liver damage (elevated gamma-glutamyltransferase). Approximately two days prior to the onset of JR's clinical signs, a large portion of the pasture had been brush hogged. None of these horses had received tetanus antitoxin or other equine serum product in the past 4-6 weeks. Based on the rapid progression of JR's clinical signs and the similarity to Rebel's current clinical signs, his owners decided to bring Rebel to Cornell.