Lavender, an 8 month old Jersey heifer, presented to the Cornell Large Animal Hospital on August 8, 2002 for a diagnostic evaluation and necropsy examination as part of a herd outbreak investigation. Eight pastured heifers out of 20 (40%) had died on the farm over the past 12 days. Their clinical signs included anorexia, depression, diarrhea, respiratory distress, muscle tremors, and death. Post-mortem examination on the farm revealed meaty lungs in addition to increased pleural and peritoneal fluid. All pastured heifers received grain once daily that was supplemented with monensin, a monovalent ionophore. No new environmental changes were noted on the farm by the owner.