Effect of Acer species (red and Freeman maple) and horse characteristics, management, and location on the in vitro oxidation of equine erythrocytes.

Abstract: Red maple toxicosis arises when horses consume wilted maple leaves, resulting in methemoglobinemia and hemolytic anemia due to oxidative damage to erythrocytes. Objective: The objective of this study was to determine how maple species (red versus Freeman maple) and horse characteristics, management, and barn site contributed to in vitro methemoglobin production and hemolysis. Methods: Horse information was obtained through an owner questionnaire. Extracts from red and Freeman maple leaves were separately incubated with washed erythrocytes from each horse (n=120). The in vitro percentage methemoglobin (%MET) and area under the hemolytic curve (AUHC) were calculated and analyzed with Factor Analysis of Mixed Data (FAMD) and multiple linear regression. Results: Extracts from both species caused methemoglobin production and hemolysis; however, %MET and AUHC for Freeman maple were 64 and 67% higher than those for red maple, respectively. In FAMD, two principal components were retained. Barn (site), Time, and %MET for both maples and AUHC for red maple, contributed to component 1, while Barn, Breed, and Body Condition contributed to component 2. Regression models explained 22% to 89% of the variation. Barn, Time, and Age contributed to red maple AUHC and %MET. While Age, Body Condition, Time, and Supplement were included within models for Freeman maple, only Barn was significant. Conclusions: Freeman maple is potentially more toxic to horses than red maple and consumption of Freeman maple leaves should be prevented. Also, Barn site was a major contributor to erythrocyte oxidation while the effects of Time and Age were minor contributors.