A b s t r a c tData on heat stress in poultry are surveyed in a two-part review. In the first part presented herein the authors summarized current knowledge on the influence of heat stress on alterations of metabolic and physiological processes in poultry as well as the adverse consequences for livability, growth, development and productivity, being 19.3-28.8 % less, and product quality (M.M. Mashaly et al., 2004; Sh. Imangulov et al., 2005). The level of these alterations depends on strength and durability of the exposure to stressing conditions, on age of birds, type and level of productivity, health status, nutrition program, complex of genetic factors, rearing conditions, etc. , 2009). The acidity and bactericide activity of gastric juice and choleretic function of liver are decreased, the balance between beneficial and detrimental segments of intestinal microbial population is altered (K. Suzuki et al., 1983; J.A. Tur, R.V. Rial, 1985) while blood supply of gastrointestinal tract, especially its upper part, is inadequate (D. Wolfenson et al., 1981). Blood vessels in skin, wattles and combs are dilated (R.U. Khan et al., 2012). Attempts to maintain the thermal homeostasis result in shallow and active breathing which is 5 to 6 times more frequent in thermal stressed (panting) birds (M.K. Sabah Elkheffi et al., 2008; A.O. Oguntunji, O.M. Alabi, 2010). That leads to increased clearance of carbon dioxide necessary for synthesis of calcium carbonate for eggshell formation, followed by subsequent increase in blood pH and respiratory alkalosis, the overall disturbance of acid-base balance (R.G. Teeter et al., 1985; A.Sh. Kavtarashvili et al., 2003; S.A. Borges et al., 2004).Keywords: temperature, heat stress, poultry, physiological changes, poultry productivity.Heat stress triggers a wide range of behavioral, physiological and immunological changes in poultry, which leads to decrease in feed consumption, «Heat stress in poultry. II. Methods and techniques for prevention and mitigation» is given in the Sel'skokhozyaistvennaya biologiya/Agricultural Biology, 2015, V. 50, ¹ 4.
