Fig. 2. The effect of embryonic heat exposure (8 h at 43°C) on hatchability in three layer strains (N=19) of fowl that differ in their heat resistance at maturity (Lohmann < Hy Line < Bedouin). Control, maintained at 37°C for the entire incubation period; 12d, heat shocked on day 12 of incubation; 18d, heat shocked on day 18 of incubation. Hatchability was markedly reduced in all strains on day 18. Different letters within each strain denote significant differences (ANOVA, P<0.05). Eggs of the Lohmann strain did not hatch at all if heat shocked on day 18.