The objective of the work was to determine under experimental conditions, the clinical and economical effects of mixed infections of the respiratory system in pigs, and to estimate the therapeutical efficacy of selected chemiotherapeutics in the treatment of experimentally induced pneumonia. Forty-two piglets, about 25 kg each, were used for the experiment. The animals were free of Mycoplasma hyopneu- moniae (M.hp.), Pasteurella multocida (P.m.) and Bordetella bronchiseptica (B.b.). Pigs were randomly divided into 6 experimental groups and a control group. All the animals were infected on day 0 with a M.hp. suspension at a dose of 10 cfu/ml. One ml of the suspension was instilled into each nostril. Seven days later the animals were infected in the same way with B.b. at a dose of 10 cfu/ml; 24 hr later they received a suspension of a toxinogenic strain of P.m., which was given into each nostril in a dose of 10 cfu/ml. Seven days after the application of P.m. the treatment of the animals was started by administering to each group of animals feed or water containing one of the following chemiotherapeutics: enrofloxacin (Baytril), lincomycin + spectinomycin (Linco-Spectin 100), norfloxacin (Quin-Abic), chlortetracyc- line + Tiamutin (Tetramutin) or Tiamutin and Tylan. All the drugs were administered in doses recommended by the producers for 10 days. The efficacy of infection and treatment was determined on the basis of on the results of the following examinations: (1) bacteriological examinations; (2) post-slaughter determination of quantitative pathological lesions in the particular lung lobes; (3) dynamics of body weight gains, and (4) feed conversion per kg of body weight gain. The results of these investigations were as follows: 1. Almost in all cases the experimental infection of piglets appeared to be effective; 2. The administration of the antibiotics eliminated M.hp. in all piglets treated with Tetramutin and Linco-Spectin for 10 days; 3. The best results in the elimination of B.b. infections were obtained in piglets treated with a combination of lincomycin+spectinomycin and Tetramutin; 4. A combination of chlortetracycline and Tiamutin proved to be most effective in the treatment of the P.m. infections in the examined piglets. This bacterium was not found in any nasal swabs collected from piglets 3 weeks after finishing the treatment. Five weeks after infecting of the animals the body weight losses in untreated piglets were about 6 kg higher in comparison with the infected and treated animals. Feed conversion was also significantly worse: in the control group feed conversion per kg of body weight gain was 4.97 kg and in piglets treated with Tetramutin and Tiamutin it was 3.68 and 3.69 kg, respectively. Comparison of the results obtained in bacteriological and post-mortem examinations with those of body weight gains and feed conversion showed a high correlation between the healthy state of piglets and effectiveness of production.
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