Effect of short periods of high incubation temperature on hatchability and incidence of embryo pathology of turkey eggs

1. Turkey eggs were incubated at 38.0 degrees and 38.5 degrees C at different stages of embryo development and for periods of 3 to 25 d. Results were compared with control eggs incubated at 37.5 degrees C. The age of mortality, the incidence of malpositions and the incidence of morphological abnormalities were recorded from all unhatched eggs. 2. Eggs incubated at 38.5 degrees C for 5 or more days hatched significantly less well than eggs incubated at 37.5 degrees C. Eggs incubated at 38.5 degrees C for 3 d hatched worse than controls but not significantly so. Eggs incubated between 0 and 25 d and 7 and 12 d but not between 0 and 6, 13 and 18 and 19 and 25 d, at 38.0 degrees C had significantly lower hatchabilities than eggs incubated at 37.5 degrees C. 3. Lowest hatchabilities were obtained when the eggs were incubated at high temperatures between 7 to 12 d and 6 to 10 d, indicating that embryos at this stage of development are more likely to succumb to high temperature than at other ages. 4. Increases in embryo mortality due to overheating were seen in weeks 3 and 4 of incubation and at the pipping stage. This was observed even when the period of overheating occurred in weeks 1 and 2 of incubation. 5. Embryos malpositioned with their head in the small end of the egg were seen at a higher incidence when overheating in the 2nd or 3rd quarter of the incubation period.