Abstract
Eggs (9120) were collected from two maternal genotypes to estimate the effects on hatchability of preincubation exposure to 38 °C for periods ranging from 0 to 7 h. Eggs from one genotype exhibited an increase in hatchability when exposed to 38 °C for 5 h. In a second experiment, exposure of eggs from two genotypes to 38 °C for 0, 5, 6 and 7 h resulted in a genotype × heat treatment interaction for hatchability. Key words: preincubation warming, hatchability, chicken eggs, meat parent genotypes, semidwarf genotypes