COMPARATIVE EMBRYONIC-DEVELOPMENT IN CHICKENS WITH DIFFERENT PATTERNSOF POSTNATAL-GROWTH

We compared embryonic development of two lines of chickens that exhibi t different patterns of postnatal growth. Classical staging techniques and morphological measurements of bone, cartilage, feather and intest ines were used to test the hypothesis that differences in postnatal gr owth would be reflected in patterns of embryonic tissue partitioning. During the second quarter of incubation, the line with higher postnata l growth staged significantly earlier (i.e., was less developed overal l) than the line with lower postnatal growth. Embryos from the Line wi th 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 growt h patterns are associated with changes in the pattern of embryonic rea llocation between tissue types, even when gross morphological differen ces are not evident at hatching. We suggest that these differences in development represent periods when the embryo is allocating to hyperpl astic growth of tissues such as muscle, as a means of increasing posth atching growth potential.