Comparative embryonic development in chickens with different patterns of postnatal growth.

We compared embryonic development of two lines of chickens that exhibit different patterns of postnatal growth. Classical staging techniques and morphological measurements of bone, cartilage, feather and intestines were used to test the hypothesis that differences in postnatal growth would be reflected in patterns of embryonic tissue partitioning. During the second quarter of incubation, the line with higher postnatal growth staged significantly earlier (i.e., was less developed overall) than the line with lower postnatal growth. Embryos from the line with higher postnatal growth exhibited less (i.e., allocated away from), bone growth (beak length, ossification of long bones), feather growth (number of feather papillae, length of primary), and eye development (number of lens sclera). There were no differences in gut development between the two lines. Our results show that different postnatal growth patterns are associated with changes in the pattern of embryonic reallocation between tissue types, even when gross morphological differences are not evident at hatching. We suggest that these differences in development represent periods when the embryo is allocating to hyperplastic growth of tissues such as muscle, as a means of increasing posthatching growth potential.