EGG CHARACTERISTICS, CARBOHYDRATE-METABOLISM, AND THYROID-HORMONES INLATE CHICK-EMBRYOS FROM DIFFERENT GENETIC LINES

Functional eggshell qualities, thyroid hormones, and carbohydrate meta bolism of chick embryos at the end of incubation were compared between a modem (Arbor Acres line) and a randombred control population (Athen s-Canadian Randombred). Embryos from the Arbor Acres genetic line deve loped in larger eggs with more albumen and less yolk than Athens Canad ian Randombred lines. Percentage shell and functional eggshell propert ies measured as eggshell conductance constants did not differ between genetic lines. On a relative basis, hearts were generally smaller and Livers heavier in Arbor Acres than in Athens-Canadian Randombred birds . Heart and liver glycogen concentrations were greater in Athens-Canad ian Randombred than in Arbor Acres embryos. However, blood glucose was greater in Randombred than in Arbor Acres embryos only at internal pi pping, a time of hypoxia and hypercapnia. Blood plasma concentrations of thyroxine did not differ significantly between the modem and Random bred embryos at any stage examined. Modern broiler chick embryos posse ssed greater concentrations of triiodothyronine as well as greater tri iodothyronine to thyroxine ratios than Randombred embryos at external pipping and hatching. It can be inferred from the data that chick embr yos differ in their use of carbohydrate during late development betwee n modern and Randombred genetic lines.