EN
The aim of the study was to attempt an explanation of the physiopathological mechanism of decreased egg-laying and increased mortality in layers infested by mass red mite Dermanyssus gallinae invasions. The study was carried out on 20 cross-breed Lohman-Brown layers, divided into two groups: control (without parasites) and experimental (infested with red mite), taken from an industrial layer house which had been subjected to a mass invasion of the parasite. Birds were kept for 8 days under conditions eliminating chicken house stress factors except for the influence of red mite in the experimental group. Following this, they were slaughtered. Corticosterone levels, haematological indices (sedimentation rate, haematocrite, hemoglobin content, RBC, WBC, TBC, level of iron) and immunological indices (content of albumin and globulins a, b, g, and acute phase proteins ceruloplasmin, haptoglobin, activity of lysozyme) were determined in the collected blood of the birds. The studies indicated a 2,5 fold increase in corticosterone levels and the tendency of a decrease in g-globulin in layers infested with red mite. It indicated the significance of stress mechanisms in decreasing the rate of egg laying and a higher mortality rate in chickens infested with Dermanyssus gallinae. The level of corticosterone may be a useful index for investigating the pathophysiological mechanisms of red mites on layers.