The combination of tylosin and doxycycline has an additional mode of action. Doxycycline belongs to the group of tetracyclines and has a bacteriostatic activity against many Gram-positive and Gram-negative bacteria like Staphylococcus spp., Diplococcus pneumonia, Streptococcus spp., Haemophilus influenza, E. coli, Pneumococci, Bacillus anthracis, Clostridium tetani and Cl. perfringens, Listeria monocytogenes, Actinomyces spp., Enterobacter spp., Klebsiella spp., Salmonella spp., Shigella spp. and Yersinia spp. Doxycycline is also active against Mycoplasma spp. (M. pneumonia), Rickettsiae and Chlamydia spp. After oral administration, doxycycline will be well resorted and effective blood levels will be obtained quickly, persisting for a considerable time.