Comparison of embryos and chicks that developed as single individuals in double yolk eggs with those that developed in single yolk eggs

Department of Poultry Science, University of Georgia, Athens 30602, USA.

Body weight and muscle characteristics of 18- to 20-d-old broiler strain embryos developing in double yolk eggs (DY) that contained one embryo and one infertile ovum were compared with embryos in single yolk eggs (SY). Similar comparisons were made in the posthatching period. In some DY eggs, the embryos were bathed in a watery yolk-like fluid with no distinct second yolk present (Type 1 embryo). In others, the second yolk was contained within the vitelline membrane and surrounded by a vascularized membrane (Type 2). These embryos were heavier than Type 1 or embryos in SY eggs by 20 d of incubation. Their Pectoralis superficialis were heavier and had significantly more protein and DNA. Chicks that hatched from the DY eggs were heavier than those that hatched from SY eggs and they had heavier P. superficialis through at least 14 d of age. Pectoralis superficialis myofibers of chicks from DY eggs had greater cross-sectional area than those from SY eggs. Myofibers in the Semimembranosus of 7- and 14 d-old chicks from DY eggs tended to be larger than those from SY eggs, but the differences were not significant. There was no difference in apparent myofiber number in the Semimembranosus of the two types of chicks. The difference in BW between the two types of chicks diminished over time, so that by 42 d of age they were virtually identical. In summary, a nutritionally enriched in ovo environment resulted in embryos and chicks with enhanced growth and muscle mass, but the effects of enrichment diminished during posthatching life and eventually disappeared.