The study was conducted to investigate the adaptation mechanisms of broiler chickens against the background of pharmacological prevention which includes combined pre-slaughter, heat and transport stress in industrial poultry farming. In summer, from clinically healthy Ross 308 chickens three groups of 95648 ± 931 chickens were formed on the principle of analogy. The first group was a control group and it was fed with complete feed. The second group was the first experimental group and it was fed with complete feed which included the anti-stress supplementary feed PIK-antistress at a dose of 1270 g per 1 ton of feed 5 days before slaughter. The third group was the second experimental group and it was fed with the anti-stress supplementary feed PIK-antistress which included L-carnitine at a dose of 1700 g per 1 ton of feed 5 days before slaughter. 38 days later broiler chickens were slaughtered. 3 main periods were commonly studied: the period after fasting, the period after transporting the chickens to the slaughter site and the period just before slaughter. Adaptation processes were developing during the slaughter of broiler chickens in summer. The processes are characterized by increasing the level of the ratio of heterophils to blood lymphocytes on average 2.8 times. The use of the complex food additive PIK-antistress and PIK-antistress in combination with L-carnitine can reduce the activity of stress-implementing mechanisms and increase the survivability of chickens by 3.20 and 4.58 %, respectively and the European productivity index by 32 and 45 units. All the data obtained are consistent with the morphometric studies of the adrenal glands while against the background of the use of anti-stress prophylaxis an increase of core area was noted by 43.0 % and 36.0 % and respectively against the background of a decrease of the area of the cytoplasm of the cortical cords by 11.2 % and 22.8 %, respectively, which indicates stabilization of metabolic processes in the cell.
