Heat stress in poultry. I. Danger, related physiological changes and symptoms

Data 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. (J.O. Ayo et al., 2006; A. Kavtarashvili, T. Kolokolnikova, 2010). Heat stress triggers a wide range of behavioral, physiological and immunological alterations in poultry (J.O. Ayo et al., 2006; P.F. Surai, T.I. Fotina, 2013) as a result of intricate interactions between decreased feed consumption up to -34.7 % (M.M. Mashaly et al., 2004; Abidin Z., Khatoon A., 2013), disturbances of endocrine (Hai B.Y.L. et al., 2000; Attia Y.A.et al., 2009) and acid-base (S.A. Borges et al., 2004) balances, impaired antioxidant status, abnormal function of definite organs and mechanisms (P. Surai, T. Fotina, 2010). Heat stress enhances the synthesis of corticosterone, noradrenaline and adrenaline which suppress releasing and distribution of steroids and gonadotropins, thus activating deregulation mechanisms fundamental for follicular growth and development as well as the ovulation (A. Yakubu et al., 2007; Y. Song et al., 2009; A.O. Oguntunji, O.M. Alabi, 2010). Additionally, the synthesis and releasing of vitellogenin necessary for the deposition of yolk is suppressed (M. Ciftci et al., 2005). The activity and efficiency of lymphoid organs such as bursa, spleen, thymus are also impaired, the numbers of monocytes, lymphocytes and heterophils are increased (O. Altan et al., 2000; S.M. Naseem et al., 2005) resulting in impaired immune response in poultry (V. Savic et al., 1993). The antioxidant status is decreased resulting in higher levels of oxidative stress when the balance between the production of free radicals and levels of antioxidants able to neutralize them is disturbed (L.T. Kadim et al., 2008). The weight of small intestine and absorbing surface of intestinal villi are also decreased by 22-23 % and 19 %, respectively (W.G. Bottie, P.C. Harrison, 1987; M.A. Mitchell, A.J. Carlisle, 1992). The functions of thyroid, particularly synthesis of T 3 hormone, and pancreas, namely secretion of trypsin, chymotrypsin and amylase, are suppressed (B.Y.L. Hai et al., 2000; Y.A. Attia et al., 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).