Toxicological studies on potentiated ionophores in chickens. III. Electrotoxicological investigations

The effect exerted by the simultaneous administration of tiamulin (40 mg/kg body mass) and a lowered dose (12 mg/kg of feed) of monensin combined with the antioxidant duokvin on the conductivity of peripheral nerve and the electrophysiological function of the heart was studied in two trials comprising 3 x 6 broiler chickens. For the study of peripheral nerve function, chickens were anaesthetized with pentobarbital sodium, the sciatic nerve (n. ischiadicus) was exposed in the sciatic arc, and bipolar stimulating and efferent electrodes were inserted directly beside the nerve, at an average distance of 20 mm from each other. For the recordings, the nerve was stimulated with 16 supramaximal impulses of 0.02 ms duration, applied at 15-s intervals. The responses given to the stimulus were recorded with the help of a polygraph and evaluated with a computer in online mode. For the study of cardiac function, the chickens were anaesthetized with methomidate. The electrocardiograms were taken in Einthoven's lead II with the help of needle electrodes, and then evaluated with computer in online mode. In control chickens, maximum conduction velocity was 30.70 +/- 0.52 m/s on the average. That value did not change after a single treatment with monensin-duokvin + tiamulin, while it underwent a slight but statistically significant decrease after two treatments. Studies on the electrical function of the heart revealed no signs of dysfunction in either of the treated groups as compared to the control.(ABSTRACT TRUNCATED AT 250 WORDS)