Alleviating heat stress in domestic fowl: different strategies

During recent decades there has been significant improvement in genetic selection of broilers and turkeys for growth rate, which has coincided with dramatic increases in metabolic rate. A similar pattern is observed in the rate of egg production by laying hens. However, this selection has not been accompanied by comparable development of visceral systems, causing inferior thermotolerance response. In parallel, scientists expect that the average global surface temperature will rise by 0.6-2.5 degrees C during the next 50 years. This situation, in which, from year to year, growth rate especially, but also egg production, improve (accompanied by increased heat production), and global surface temperature increases, demands an efficient means to improve the acquisition of thermotolerance by domestic fowl exposed to hot climatic conditions, and to do so economically. To develop thermotolerance three direct responses are employed: the rapid thermal stress response (RTSR), acclimation/acclimatization, and epigenetic temperature adaptation. This review will focus on the advantages and disadvantages of the different strategies used to reach the conflicting goals of production on the one hand and thermotolerance on the other hand.