Simultaneous treatment of chickens with salinomycin and tiamulin in feed.

Laboratory and field experiments involving more than 100,000 birds were performed to assess the effect of simultaneous in-feed medication of chickens with salinomycin and tiamulin at various concentrations. In an artificial infection study with Mycoplasma gallisepticum, low levels of tiamulin (10-40 ppm) did not induce signs of ionophore intoxication with salinomycin at 60 ppm in the feed, whereas levels of 50 ppm caused early signs with a mild growth depression. A level of 20 ppm gave a maximum average improvement in growth rate of 12.5%. There was a dose-related response in mycoplasma lesion inhibition, with 50 ppm reducing lesions by 75%. In the two field trials, chickens suffering from mycoplasmosis complicated with infectious bronchitis and receiving 60 ppm salinomycin in the feed showed marked improvements in mortality rates, lesion scores, and feed-conversion efficiency when tiamulin was added at 20 ppm and 30 ppm in the feed. There were no signs of incompatibility between the two antibiotics at these levels.