Red maple (Acer rubrum) leaf toxicosis in horses: a retrospective study of 32 cases.
Authors: Alward Ashley, Corriher Candice A, Barton Michelle H, Sellon Debra C, Blikslager Anthony T, Jones Samuel L
Journal: Journal of veterinary internal medicine
Summary
# Red Maple Leaf Toxicosis: Prognostic Factors and Treatment Considerations Red maple (*Acer rubrum*) toxicosis in horses causes severe haemolytic anaemia and methemoglobin formation, yet little evidence exists regarding factors that influence survival outcomes—a gap this retrospective multi-institutional study sought to address by analysing 32 cases from south-eastern US referral hospitals. Affected horses presented with diverse clinical complications including anaemia (29 cases), systemic inflammation (24 cases), renal insufficiency (41%), laminitis and colic, though notably the latter two conditions did not negatively impact short-term survival. A striking finding emerged regarding corticosteroid administration: horses receiving corticosteroids had significantly increased mortality risk (P = 0.045), whilst those that survived to discharge were paradoxically more likely to have developed pyrexia during hospitalisation (P = 0.030)—suggesting fever may indicate a beneficial inflammatory response. Initial laboratory parameters including haemoglobin, methemoglobin and percentage methemoglobin concentrations proved poor predictors of mortality, implying that severity of initial presentation does not reliably indicate prognosis. For practitioners, these findings challenge conventional assumptions about prognostication and raise important questions about corticosteroid use in red maple toxicosis management, warranting caution with immunosuppressive therapy and supporting a more conservative, expectant approach to treatment in these cases.
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Practical Takeaways
- •Red maple leaf toxicosis causes severe hemolytic anemia with high mortality (59%); monitor for signs of poisoning if wilted leaves are accessible to horses
- •Avoid corticosteroid administration in red maple toxicosis cases, as it significantly worsens prognosis
- •Development of fever during hospitalization is a favorable prognostic indicator; initial blood parameters alone cannot predict survival outcomes
Key Findings
- •Of 32 horses with red maple toxicosis, 19 died (59% mortality); 29 presented with anemia and 24 with clinicopathologic evidence of systemic inflammation
- •Renal insufficiency occurred in 41% (12/30) of horses; laminitis and colic did not negatively impact short-term survival
- •Horses that survived were significantly more likely to have developed pyrexia during hospitalization (P = 0.030)
- •Corticosteroid treatment was associated with significantly increased likelihood of death (P = 0.045); initial hemoglobin and methemoglobin concentrations did not predict mortality