Red Maple (Acer rubrum) Leaf Toxicosis in Horses: A Retrospective Study of 32 Cases

Abstract

Ingestion of wilted red maple leaves by horses can result in severe hemolytic anemia and methemoglobinemia. Little is known about what factors influence the outcome of red maple leaf toxicosis in horses. Our hypothesis was that physical examination findings, clinicopathologic variables or therapeutic modalities may predict outcome in horses with red maple leaf toxicity. Horses with red maple leaf toxicosis presented to referral hospitals in the southeast region of the United States. A multi-institutional retrospective study was designed to identify factors that predict mortality in horses with red maple toxicosis. Thirty-two horses with red maple toxicosis were identified, 19 of which died. Twenty-nine horses presented with anemia and 24 had clinicopathologic evidence of systemic inflammation. Renal insufficiency was identified in 12/30 (41%) horses. Laminitis (9/28) and colic (13/30) also were identified in horses with red maple toxicosis, but development of these 2 conditions did not have a negative effect on short-term survival. Horses with red maple toxicosis that survived to discharge were likely to have developed pyrexia during hospitalization (P = .030). Horses that were treated with a corticosteroid had a significantly increased likelihood of death (P = .045). There was no significant relationship between initial serum hemoglobin concentration, methemoglobin concentration, or percentage methemoglobin and mortality in this horse series. This study suggests that information obtained on initial examination cannot be used to accurately predict survival in horses with red maple toxicosis, but horses that receive corticosteroids are unlikely to survive.