Acute hemolytic anemia, methemoglobinemia, and heinz body formation associated with ingestion of red maple leaves by horses.

This research identifies a correlation between the consumption of red maple leaves by horses and the development of acute hemolytic anemia, a condition where red blood cells are destroyed faster than they can be produced. Additionally, methemoglobinemia, a disorder characterized by a higher than normal level of a specific type of hemoglobin that cannot release oxygen effectively, and Heinz body formation, indicative of oxidative damage to the red blood cells, were also observed.

Research Context and Cases

• The study period spanned from June 1975 to June 1979 during which acute hemolytic anemia was diagnosed in 11 horses across 7 different farms in New York.
• Of the 7 horses that succumbed to their condition, 6 exhibited signs of methemoglobinemia.
• The 4 horses that managed to recover from the illness did not display any symptoms of methemoglobinemia. However, Heinz body formations were detected in the blood samples of 3 of these 4 horses.
• In the discussed cases, there seemed to be a possible correlation between the manifestation of methemoglobinemia and Heinz body formation in the hemolytic process.
• Apart from the 11 specified cases, 22 more clinically similar cases were reported from various locations including New York, Pennsylvania, and the New England states.
• All of the mentioned cases of hemolytic anemia occurred between June and October, a time period when horses had access to a variety of native grasses, weeds, and trees in the outdoors.

Association with Red Maple Leaves and Red Maple Trees

• On two farms, horses were observed developing hemolytic anemia after browsing branches of red maple trees that had fallen.
• In an attempt to understand the possible correlation, 1 kg of a mixed leaf and bark sample from the red maple tree was fed to two ponies.
• The ponies started showing signs of illness within 48 hours characterized by methemoglobinemia and intravascular hemolysis, which is the destruction of red blood cells.
• Both ponies died within 5 and 6 days, revealing extremely low packed cell volumes of 6% and 7%, hinting at severe anemia.

Conclusions and Limitations

• Results from the research suggest a strong link between many cases of hemolytic anemia in horses in northeastern states and the ingestion of red maple leaves or bark.
• Though the cause of the disease seems to have been identified, the study did not manage to determine the factors that made certain horses more susceptible to poisoning from red maple leaves or bark.
• Furthermore, the research does not discount the possibility of other environmental toxins contributing to the illness alongside red maple leaves or bark.