EFFECTS OF SHORT PERIODS OF LOW TEMPERATURE STRESS AT 17 DAYS INCUBATION ON HATCHABILITY AND EMBRYONIC DEVELOPMENT

Four groups of 80 eggs each were subjected to a low temperature stress of 3.8 C for 0, 4, 5, or 8 h, respectively, commencing after 17 days (408 h) incubation. Samples of these eggs were examined at 18.0, 19.5, 20.5, and 21.5 days incubation to study the treatment effect on embryonic development, and the remainder of the eggs were incubated for 22 days to determine the effect on hatchability. Hatchability was significantly reduced by 5 and 8 h of exposure to 3.8 C whereas 4 h of exposure caused a nonsignificant reduction in hatchability. Examination of embryos that failed to hatch revealed a high incidence of malpositions and abnormal hatching muscles. Malpositions occurred as early as 18 days incubation whereas edema, or hemorrhage, or both, of the hatching muscle did not begin to develop until 19.5 days. By 20.5 days of age the hatching muscles of the 8-h stressed group were significantly heavier than all other groups. The weight of the hatching muscle from the 5- and 8-h exposure groups increased continually during incubation whereas those of the controls and 4-h stress group had begun to decrease by 20.5 days and 21.5 days, respectively.