Equine

Research Abstract

E23 - Acute, Subacute and Chronic Assessment of Horses Exposed to Lethal and Sublethal Doses of Monensin

Thursday, June 14
5:45 PM - 6:00 PM
Location: WSCC 620

Monensin is highly toxic to horses and inadvertent ingestion can result in cardiac dysfunction and death. The objectives of this prospective study were to determine the cardiovascular and athletic outcome of horses exposed to monensin.

Physical examination, exercise stress testing, ECG (pre- and during exercise) and echocardiography (pre- and post-exercise) were performed in 76 horses exposed to monensin-contaminated feed. Four horses were examined within 2 weeks of exposure (acute period). Twenty-nine horses were examined between 15 and 45 days post-exposure (subacute period) and 70 horses were examined after 4 to 10 months of rest (chronic period). Follow-up information was obtained by telephone interviews approximately 16 months after exposure for 56 horses.

Three of the 4 horses (75 %) presented during the acute period died or were euthanized; all horses had clinical signs and cardiac anomalies at rest. Nineteen of the 29 horses (66 %) examined during the subacute period had cardiac anomalies (upon physical examination (11), cardiac examination at rest (16) and with exercise (5)). Four to 10 months after exposure, 31 of the 70 horses (44 %) had cardiac abnormalities (upon physical examination (6), cardiac examination at rest (22) and with exercise (13)). Sixteen months after exposure, 34 (53 %) of the 64 horses with known outcome had returned to their intended use, including 10 horses with cardiac anomalies in the previous months.

Clinical outcome of horses exposed to sublethal doses of monensin is highly variable and commonly result in long-term cardiac dysfunction leading to exercise intolerance and even death. 

Clémentine Gy, DVM

Resident in Large Animal Internal Medicine (Equin)
Université de Montréal

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