Treatment and prevention of infections caused by germs sensitive to tylosin and/or doxycycline. Among them: infections of the respiratory, digestive and urogenital systems, such as: mycoplasmosis, CRD, coryza, colibacillosis, omphalitis and infection of the vitelline sac, avian cholera, enteritis and diarrhea, necrotic enteritis, sacculitis, sinusitis, synovitis, staphylococcosis, streptococcosis, corinebacteriosis, hexa-mitiasis and leptospirosis. Prevention of secondary bacterial infections following viral infections, stress conditions, vaccinations, re-lodging, beak trimming, transportation, feed and climate changes.