EVALUATION OF THE CARDIOMYOTOXIC EFFECTS OF DOXYCYCLINE OVERDOSE IN CALVES USING 2-DIMENSIONAL SPECKLE TRACKING.

Doxycycline (DOXY) is associated with left ventricular (LV) dysfunction in calves in accidental overdose but not in experimental models when evaluated with classical and Doppler echocardiography. Two-dimensional-speckle tracking (2DST) is used to evaluate LV dysfunction in numerous species but not in cattle. The aim of this study was to evaluate the cardiotoxic effects of an experimental overdose of DOXY using 2DST in calves. Ten healthy male Holstein calves. Group 1: 5 calves (mean age 58.0 +/- 16.3 days; mean body weight 72.2 +/- 13.0 kg) received 25 mg/kg of DOXY orally for 5 days. Group 2: 5 calves (mean age 56.4 +/- 15.7 days; mean body weight 73.4 +/- 7.0 kg) received a placebo. Electrocardiography (ECG) and 2DST echocardiography were performed at day 0 and day 8. ECG tracings were analysed for occurrence of arrhythmias. 2DST measurements included global and segmental, peak values for radial and circumferential strains (SR, SC), strain rates (SrR, SrC), rotation (Rot), rotation rates (RotR) and radial displacement (DR). All calves completed the study. ECG recordings were unremarkable in both groups. Heart rate was neither significantly different between groups nor before and after treatment. LV systolic function was affected in calves receiving an overdose of DOXY as shown by a significant decrease of segmental SR (P < 0.05), SC (P < 0.05) and DR (P < 0.05) in treated calves compared to the placebo group in several segments. The SrC in early diastole was also significantly decreased in 1 segment (<0.05). In calves, DOXY overdose induces a LV dysfunction in systole, and to a lesser extent, in diastole. A better comprehension of the pathophysiology involved in the DOXY overdose will help in the treatment of accidental cases.