Physiology and Endocrinology: Nutrition, Growth and Stress

ratios of insulin to glucagon (I/G) from 14E to 17E ranged from 1.8 to 2.2 which were significantly greater than normal I/G ratio in the postabsorptive state in avian species (1.2-1.7). The results indicate that insulin is an important promoter of chick embryo growth by anabolic drive to promote protein deposition especially during the embryonic rapid growth period. There also was a significant increase in plasma glucose from 13E to 18E suggesting glucose is an important regulator of protein anabolism in the chick embryo via suppression of amino acid oxidation. Plasma IGF-1 and IGF-II levels increased from 10E to 14E and then IGF-1 slowly decreased until hatch, while IGF-II remained constant. IGF-II levels were about 10 fold greater than IGF-1 suggesting IGF-II is an important functionary for chick embryonic development. Plasma T3 and T4 levels showed a significant increase during the third week of incubation and reached a peak at 19-20 E. The findings are consistent with previous research showing a sharp rise in T3 and T4 activities when the embryo switches to lung respiration.