COMPARISON OF EMBRYOS AND CHICKS THAT DEVELOPED AS SINGLE INDIVIDUALSIN DOUBLE YOLK EGGS WITH THOSE THAT DEVELOPED IN SINGLE YOLK EGGS

Body weight and muscle characteristics of 18- to 20-d-old broiler stra in embryos developing in double yolk eggs (DY) that contained one embr yo and one infertile ovum were compared with embryos in single yolk eg gs (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 secon d 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 superf icialis were heavier and had significantly more protein and DNA. Chick s that hatched from the DY eggs were heavier than those that hatched f rom SY eggs and they had heavier P. superficialis through at least 14 d of age. Pectoralis superficialis myofibers of chicks from DY eggs ha d greater cross-sectional area than those from SY eggs. Myofibers in t he 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 signific ant. There was no difference in apparent myofiber number in the Semime mbranosus 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 m uscle mass, but the effects of enrichment diminished during posthatchi ng life and eventually disappeared.