Oxalate (Rumex venosus) poisoning in cattle.

Fifteen range cows died of oxalate poisoning caused by ingestion of Rumex venosus. Ecchymotic and petechial hemorrhages were prominent on the abdominal serosal surfaces. Approximately 2 L of thin, yellowish fluid was in the abdominal cavity, and mesenteric lymph nodes were enlarged and edematous. Other findings included catarrhal abomasitis; enteritis; pale, edematous kidneys; congested lungs; fatty infiltration of the liver; and nephrosis. In the kidneys, birefringent crystals resembling oxalate crystals were demonstrable only when frozen sections were examined.