A case of red maple (Acer rubrum) toxicity associated with fallen branches

Acute colic in a Dartmoor pony

“…1,2 Affected animals will develop acute, severe hemolysis with hemoglobinemia and/or methemoglobinemia within 18 to 48 hours post-consumption of the fallen leaves, as seen in this particular case. [1][2][3] Toxicity is typically seen in the fall or early spring when the melting snow uncovers previously fallen leaves. [1][2][3] There is a correlation between the amount of leaf decay and the toxic potency of the leaves to horses.…”

“…[1][2][3] Toxicity is typically seen in the fall or early spring when the melting snow uncovers previously fallen leaves. [1][2][3] There is a correlation between the amount of leaf decay and the toxic potency of the leaves to horses. 2 Typically, the disease only develops with the consumption of partially decayed to completely dead leaves, which may remain toxic for weeks.…”

“…1,2 It is believed that the dead leaves generate potent oxidants which overcome the glutathionereducing system in red blood cells resulting in the formation of Heinz bodies. 2,3 Heinz bodies weaken the integrity of the red blood cell membrane allowing for osmotic lysis and the release of hemoglobin (hemoglobinemia). Hemoglobinuria develops once the renal reabsorption threshold for hemoglobin is surpassed.…”

“…4 In addition to anemia, oxygen delivery is further exacerbated by the oxidation of free hemoglobin to form methemoglobin. 3 Reduced oxygen-carrying capacity deprives the horse of oxygen and results in shock and renal nephrosis. Pooled hemoglobin casts within the tubules may block the tubules and lead to partial or complete obstruction.…”

“…4 A cycle is created as obstruction creates further tubular necrosis and degeneration which leads to decreased resorption and increased pooling of hemoglobin. 3 Clinical signs associated with red maple toxicity include depression, lethargy, anorexia, colic, dark brown or red urine (hemoglobinuria or methemoglobinuria), muddy brown or cyanotic membranes, anemia, icterus, and Heinz bodies on cytology. [1][2][3] The disease most commonly manifests as a hemolytic crisis with hemoglobinuria or methemoglobinuria, but both can occur leading to a poorer prognosis.…”