Cardiac troponin I (cTnI) is used as a biomarker of myocardial injury in people and small animals. Little is known about the diagnostic use of cTnI in cattle. Serum cTnI correlates to myocardial function and histopathologic lesions in cattle with monensin-induced myocardial injury. Ten healthy cows. Experimental study. Animals received 1 dose of monensin PO; 30 mg/kg (n = 1) or 40 mg/kg (n = 1) (Group A) or 50 mg/kg monensin (n = 8) (Group B) of body weight. Repeated measurements were performed of serum cTnI, biochemistry, and ECG and echocardiography until study termination at 80 (Group A) and 144 hours (Group B) after dosing. Semiquantitative histopathologic examinations of the heart were performed in each cow. A scoring system with regard to the magnitude of myocardial injury was established and a total heart score was compared with maximum cTnI concentration measured after monensin administration. Five hearts from healthy cows served as controls. Increased cTnI (>0.07 ng/mL) was found in 9/10 cows. cTnI was significantly associated with left ventricular shortening fraction (r(2)= 0.51; P= .02) and myocardial histopathologic lesion score (r(2)= 0.49; P= .021). All cows (n = 7) with evidence of myocardial necrosis had a cTnI concentration > or = 1.04 ng/mL. cTnI is related to myocardial necrosis and severity of myocardial damage in cattle with monensin toxicosis. cTnI could become a useful diagnostic tool in the noninvasive assessment of myocardial injury in cattle with naturally occurring cardiac disease.
