Recent decades have seen significant progress in the genetic selection of fast-growing meat-type broiler chickens. However, fast growth has coincided with inferior development of the visceral systems, contributing to the difficulties of broilers in coping with heat stress. The late 19th and 20th centuries were characterized by an increased global mean surface temperature which is expected to rise during the next fifty years. This situation, where growth rate (heat production) improves on a yearly basis and the future foresees an increase in global surface temperature, demands an efficient means to economically improve the acquisition of thermotolerance by broiler chickens facing hot climatic conditions. In homeotherms, three direct responses are exhibited to develop thermotolerance acquisition: the rapid thermal shock response, acclimation and epigenetic adaptation. This paper will focus on air velocity as a principal parameter which dramatically affects sensible heat loss and its contribution to the ability of acclimated or epigenetic adapted broilers to maintain efficiently there energy balance under hot conditions. The following studies demonstrated that: a. air velocity plays a major role in the broiler’s energy balance capacity under high ambient temperatures; b. the optimal air velocity for achieving maximal growth performance differ with ambient temperature and has turning point at ambient temperature below 30°C, where chilling effect affects the broiler; c. high air velocity at high ambient temperatures affects the ability of broilers to maintain total body water, most probably as result of cutanious water loss; d. thermal hot conditioning at an early age increases the capacity of broilers to efficiently lose heat by radiation and convection; e. the improvement of genetic selection for growth performance, dominate to some extend the physiological needs to maintain energy and water balance.

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