Undergraduate Honors Thesis Projects

Date of Award


Document Type

Honors Paper

Degree Name



Biology & Earth Science


Jeffrey S. Lehman, Ph.D.

First Committee Member

Jeffrey S. Lehman, Ph.D.

Second Committee Member

Erik P. Rothacker, Ph.D.

Third Committee Member

Louise Captein


Acer phylogeny, Equine, Toxicity, Hemolysis, Methemoglobinemia, Red Maple Toxicosis

Subject Categories

Biology | Life Sciences | Other Plant Sciences | Plant Biology | Plant Sciences | Veterinary Medicine


Red maple toxicosis is a phenomenon that occurs in equines after the consumption of dried or wilted red maple (Acer rubrum L.) leaves. Within the erythrocytes, it causes hemolysis, methemoglobinemia, and Heinz body development. The toxic agent of red maple leaves has not yet been identified; however, the development of hemolytic anemia and methemoglobinemia in equines after ingestion of the leaves, suggests that the toxin is acting as a strong oxidant. Some studies have noted that not only are wilted red maples leaves toxic to equines, but that wilted leaves of other maple species may also be toxic. Therefore, the objective of this research was to evaluate the toxic effects of dried samples of A. rubrum, as well as thirteen other species within the genus Acer, on the hemolysis of equine erythrocytes. Two-year old saplings were evaluated in greenhouse and field experiments of 5 and 3 replicates, respectively. Leaves were harvested and dried throughout two growing seasons. The leaf material was suspended in water (0.05 g material/500 μl water) and incubated with equine blood taken from the horses housed at the Austin E. Knowlton Equine Center for two and three hours in 1.5 ml microfuge tubes for determination of percentage hemolysis and percentage methemoglobin, respectively. Relative toxicities of species were determined spectrophotometrically based on percentage hemolysis of erythrocytes and percentage methemoglobin formation. Acer species differed significantly for hemolysis and methmoglobin production. In the greenhouse, the red×silver hybrid maple exhibited the largest amount of hemolysis (2 to 3 times that of the control), as well as a high level of methemoglobin formation (~69%). In contrast, Norway maple caused little hemolysis and methemoglobin. The results of this study show toxicity to equine erythrocytes may occur in multiple species throughout the Acer genus, indicating that the toxic component may be an ancestral trait that has been lost in some taxa.

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