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

Overview

• This study investigated how different species of maple trees (red maple and Freeman maple), along with horse characteristics, management practices, and barn location, affect the oxidative damage to horse red blood cells in vitro.
• The research found that Freeman maple causes greater oxidative damage than red maple, and that barn location significantly influences this damage.

Background and Objective

• Red maple toxicosis occurs when horses eat wilted leaves from the red maple tree, leading to methemoglobinemia (an abnormal amount of methemoglobin in the blood) and hemolytic anemia (destruction of red blood cells caused by oxidative damage).
• The main objective was to examine whether the species of maple (red vs. Freeman), plus horse characteristics (such as age, breed, body condition), management (diet supplements, time factors), and barn location affect the in vitro production of methemoglobin and hemolysis in horse erythrocytes.

Methods

• Data collection involved an owner questionnaire to gather information on individual horse characteristics and management.
• Leaf extracts were prepared from red maple and Freeman maple leaves separately.
• Washed erythrocytes (red blood cells) from 120 horses were incubated with the leaf extracts in vitro.
• The two primary measurements were:
  • % Methemoglobin (%MET) produced, indicating the extent of oxidative conversion of hemoglobin.
  • Area under the hemolytic curve (AUHC), reflecting the degree of red blood cell destruction over time due to oxidative stress.
• Statistical analysis included Factor Analysis of Mixed Data (FAMD) to reduce and interpret complex variable relationships and multiple linear regression to understand contributions of variables to oxidation and hemolysis outcomes.

Results

• Both red maple and Freeman maple leaf extracts induced methemoglobin formation and hemolysis in horse erythrocytes.
• Freeman maple extract caused substantially higher oxidative damage:
  • 64% higher %MET (methemoglobin production) compared to red maple.
  • 67% higher AUHC (hemolysis) than red maple.
• Factor Analysis of Mixed Data (FAMD):
  • Identified two principal components explaining most variability.
  • Component 1 was influenced by barn location, time, %MET for both maples, and AUHC for red maple.
  • Component 2 was influenced by barn, horse breed, and body condition.
• Multiple linear regression:
  • Explained between 22% and 89% of the variation in oxidative damage measures.
  • For red maple, barn location, time, and age were significant contributors to AUHC and %MET.
  • For Freeman maple, barn location was the only significant contributor, while age, body condition, time, and dietary supplements were considered but not significant.

Conclusions

• Freeman maple poses a potentially greater oxidative risk to horses than red maple, suggesting that consumption of Freeman maple leaves should be avoided.
• Barn location (site-specific factors, potentially related to environmental or management conditions) plays a major role in erythrocyte oxidative damage; this may influence the susceptibility of horses to maple-induced toxicity.
• Time (likely time of year or duration of exposure) and age were minor but still contributory factors to the extent of oxidative damage.
• Findings highlight the importance of identifying maple species in grazing and reducing exposure to toxic leaves, especially Freeman maple, to protect horse health.