EN
The aim of the study was to determine the influence of some pathogens on the serum level and dynamics of chicken cystatin and a1-protease inhibitor. The experiment was carried out on 150 Starbro chickens that were randomly selected into 6 groups. Group I was the control, group II and III were infected with REO virus and Marek's disease virus, group IV with invasive Eimeria oocysts, and V and VI with E. coli and S. aureus respectively. The level of chicken cystatin was determined by ELISA test and a1-protease inhibitor as an antitrypsin capacity. It was demonstrated that the concentration of chicken cystatin increased in chickens with the virus infection REO and MDV by about 54% and 29%, while with E. coli and S. aureus by 43%. The smallest changes, observed in chickens infected with Eimeria oocyst, amounted to 16%. In contrast, the authors only observed an increase of the level a1-protease inhibitor in coccidiosis. The authors postulate that chicken cystatin is more useful as a diagnostic parameter than a1-protease inhibitor in the analysed diseases.