A 7-year-old pastured mare suffered an acute onset of hemolytic anemia and hematuria. The blood drawn for analysis was hemolyzed and dark. The mare died about three hours after intravenous fluid therapy was begun. Whole blood, serum and a blood smear were submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) for evaluation.
Clinical differentials included ehrlichiosis, methemoglobinemia, equine infectious anemia, liver failure and toxicity, and the samples came with a specific request to look for Heinz bodies. The following parameters were elevated when measured in the severely hemolyzed serum: BUN, 63.1 (9-20 mg/dl); creatinine, 3.1 (0.9-1.7 mg/dl); total bilirubin, 7.1 (0.7-2.6 mg/dl); direct bilirubin, 1.0 (0.1-0.3 mg/dl); and creatine kinase, 672 (93-348 U/L). Values for AST and GGT were also elevated. A CBC was not possible, as all RBCs in the entire blood sample were completely lysed.
Onion (Allium sp.) and wilted maple leaf (Acer sp.) ingestion were suggested as possible differentials. Several days later, the vet called back to let us know that a tree in the horse pasture had been badly damaged by storms and branches had been down for several days before the horse began to show clinical signs. The owners thought it might have been a maple, but had burned it to clear the debris, so confirmation was not possible. A saponin in wilted maple leaves causes intravascular hemolysis and subsequent death in horses. During periods of stormy weather, cases of wilted maple poisoning in horses could occur wherever maple trees are damaged. Owners should be aware of such trees on their properties.
