391ANTIOXIDANT SYSTEMS IN POULTRY BIOLOGY: HEAT SHOCK PROTEINSCommercial poultry production is associated with various stresses decreasing productive and reproductive performance of birds. A growing body of evidence indicates that most of stresses in poultry production at the cellular level are associated with oxidative stress due to excess of free radical production or inadequate antioxidant protection. Recently, a concept of the cellular antioxidant defence has been revised with a special attention paid to cell signalling. Antioxidant systems of the living cell are based on three major levels of defence and include several options and vitagene activation in stress conditions is considered as a fundamental adaptive mechanism. The vitagene family includes various genes responsible for synthesis of protective molecules such as thioredoxins, SOD, sirtuins and heat shock proteins (HSP). Indeed, HSP70, HSP90 and HSP32 (heme oxygenase) are among important elements of the antioxidant system network. However, by the time of writing no comprehensive review on the roles and effects of HSPs in poultry biology has appeared. Therefore, the aim of this review is a critical analysis of the role of HSPs in poultry biology with specific emphasis to their functions as an essential part of the vitagene network. From the analysis of the recent data related to HSPs in poultry physiology and adaptation to stresses it is possible to conclude that: a) HSPs as important vitagenes are the main driving force in cell/body adaptation to various stress conditions. Indeed, in stress conditions synthesis of most cellular proteins decreases while HSP expression is usually significantly increased; b) HSPs as cellular chaperones are responsible for proteostasis and involved in protein quality control in the cell to prevent misfolding or to facilitate degradation, making sure that proteins are in optimal structure for their biological activities; c) there are tissue-specific differences in HSP expression which also depends on the strength of such stress-factors as heat, heavy metals, mycotoxins and other toxicants; d) HSP70, HSP90 and HSP32 are shown to be protective in heat stress, toxicity stress as well as in other oxidative stress-related conditions in poultry production; e) molecular mechanisms of HSP participation in acquisition of thermotolerance need further detailed investigation; f) there are complex interactions inside the antioxidant network of the cell/body to ensure an effective maintenance of homeostasis in stress conditions. Indeed, in many cases nutritional antioxidants (vitamin E, ascorbic acid, selenium) in the feed can decrease oxidative stress and as a result HSP expression could be decreased as well; g) regulating effects of various phytochemicals on HSPs need further investigation; h) protective effects of HSPs in the immune system in stress conditions await practical applications in poultry production; i) nutritional means of additional HSP upregulation in stress conditions of poultry production and physiological and commercial consequences await investigation; j) vitagene upregulation in stress conditions is emerging as an effective means for stress management psurai@feedfood.co.ukReview5122015Antioxidant system,chicken,HSP,Poultry,Stress,VitagenesPeter F. SuraiDepartment of Microbiology and Biochemistry, Faculty of Veterinary Medicine, Trakia University, Stara Zagora 6000, Bulgaria