These studies have demonstrated that heat
conditioning of chickens during the first week posthatch can induce reduction in body temperature (Tb) and mortality rate during subsequent thermal challenge
However, such treatments are difficult to use in practice, and using such a procedure during embryogenesis might achieve better results and be easier toperform.Thermalmanipulation(TM)ofchickembryos has recently been addressed by Yahav et al. (2004a,b), andtheyreportedareductioninTb,plasmatriiodothyronine and corticosterone concentrations in 3-d-old chicks thermally manipulated during different phases of embryogenesis and exposed to several incubating temperatures. The mechanisms favoring better thermotolerance inheat-conditioned chicksmightinvolvebothanincrease in their capacity for thermolysis or a decrease in their thermogenic potentia