Comparison of the antimycoplasma activity of two commercially available tylosin premixes.

Two tylosin premixes (referred to in this report as Premix A and tylosin Premix B), obtained as commercial products from Japan, were analyzed microbiologically for tylosin and by high pressure liquid chromatography (HPLC) for macrolide content. They were evaluated in the feed at concentrations of 550 and 1100 ppm antibiotic activity for the treatment of chickens with induced Mycoplasma gallisepticum (MG) infection. The tylosin microbiological assay value for Premix A was 3.0% below and for Premix B, 7.5% above the tylosin concentration stated on the respective premix labels. Analyses by HPLC showed tylosin Premix A contained 84% tylosin and 16% other macrolide derivatives; whereas, tylosin Premix B contained 42.6% tylosin, 46.6% other macrolides, and 10.8% unidentified material. When the two premixes were administered in the feed for 5 days as treatments for MG-infected chickens, tylosin Premix A was significantly more effective than tylosin Premix B, as measured by reductions in mortality, air sac lesions, and infection as indicated by development of MG antibody. In experiments in pigs where individual macrolide derivatives were used, tylosin was more effective than the other macrolides, desmycosin or macrocin, for the treatment of Mycoplasma hyopneumoniae infection. It is apparent from these studies that commercially available tylosin products may contain varying quantities of tylosin and related macrolide antibiotics and that these differences may significantly affect the efficacy of the products.