EN
Studies were carried out on 32 one-day-old broiler chickens, which were divided into a control and 3 experimental groups. Chickens in the control groups were fed, for 8 weeks with basic feeds, while chickens in the experimental groups were fed basic feeds enriched with monensin-natrium at the following doses: group I — 100 ppm, group II — 70 ppm and group III — 50 ppm. During the course and at the end of the experiment liver, kidneys, pancreas and heart were removed from both the control and experimental chickens for microscopic examination. First structural changes in the form of a small degree fat — droplet formation in liver cells were observed after 4 weeks of the experiment. 8 weeks after the beginning of the experiment, a significant degree of fat — droplet formation and swelling of Golgi apparatus structure were noted. The changes observed were associated with side — effect of coccidiostatic action on the liver of the experimental broiler chickens.