Key words: egg storage, embryonic development, albumen quality, hatchability, chick quality
It is well known that an increase in the storage duration increases incubation duration and decreases hatchability and chick quality. The negative effects of prolonged egg storage (> 7 days) may be caused by changes in the embryo, in the egg characteristics, or by both. The first aim of the current thesis was to investigate which physiological mechanisms are involved in the negative effects of prolonged egg storage on hatchability and chick quality. The second aim was to investigate how these negative effects of prolonged egg storage can be reduced by making changes in storage or early incubation conditions. Treatments, such as prestorage incubation, frequent warming during storage, a change in the storage air composition, different preincubation warming profiles, and hypercapnic incubation during the first 5 days of incubation were used in the current thesis to gain more insight in the cause of the negative effects of prolonged egg storage. Prestorage incubation and frequent warming during storage increased the stage of embryonic development and the number of viable embryonic cells. The effect of these treatments on hatchability was nihil, positive or negative and seems to depend on the stage of embryonic development before and after the treatment. The storage air compositions, studied in the current thesis did not affect embryonic development, hatchability, or chick quality, when eggs were stored for 14 days. This suggests that changes in albumen quality during storage do not affect hatchability and chick quality. The 24-h preincubation warming profile decreased embryonic mortality during the first 9 days of incubation in comparison with the 4-h preincubation warming profile when eggs were stored for 13 days. Hypercapnic incubation during the first 5 days of incubation decreased albumen pH during early incubation, but did not improve hatchability. In conclusion, embryo characteristics seem to have a more important role in the negative effects of prolonged egg storage than changes in the egg characteristics, such as changes in the albumen pH and albumen height.