Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/18/2006
Publication Date: 4/1/2007
Citation: Lu, J.W., McMurtry, J.P., Coon, C.N. 2007. Developmental changes of plasma insulin, glucagon, insulin-like growth factors, thyroid hormones, and glucose concentrations in chick embryos and hatched chicks. Poultry Science. 86:673-683. Interpretive Summary: Many factors, including several hormones, are known to be important for optimal avian embryogenesis to occur. Although many of these hormones have been previously documented to be present in the general circulation at different times during embryo development, to date no study has evaluated these specific hormones in a single experiment, and also determined if the sex of the embryo influenced hormone blood levels. In this study hormone (insulin-like growth factors-I and –II, insulin, glucagon, triiodothyronine, thyroxine) were determined in broiler chickens from early embryonic development thru 3 weeks after hatching in both sexes. No difference in any hormone levels between the sexes were noted except for the period immediately after hatching when thyroxine levels were observed to be greater in females than in males. Hormone concentrations varied depending on the stage of embryogenesis after hatching. The results of this study suggest that insulin and insulin-like growth factor-II are potentially more important functionaries in the chick embryo than previously reported. This information will be of interest to other scientists.
Technical Abstract: The developmental hormonal changes in Cobb 500 chick embryos and hatched chicks were determined by measuring plasma insulin, glucagon, IGF-I, IGF-II, triiodothyronine, thyroxine, and glucose concentrations at different ages of chick embryos and hatched chicks. Plasma samples were obtained daily from 10 days of embryogenesis (10E) through 13 days post-hatch and at 17 and 21 days post-hatch. A significant increase in plasma insulin was observed with increasing age from 10E to hatch. Plasma glucagon levels remained low until 17E, and then significantly increased approximately 3-fold at hatch which corresponded to increasing plasma glucose levels during late embryo development. The plasma insulin to glucagon molar ratio (Intogl) from 14E to 17E of incubation ranged from 2 to 4, and was significantly higher than any other time during incubation. These results indicate that insulin may be an important promoter of chick embryonic growth by anabolic drive to promote protein deposition. Insulin and glucagon increased after hatch, which may be due to increased feed consumption and an increased utilization of carbohydrates as the key energy source compared to nutrients obtained through lipolysis and proteolysis in the embryos. Plasma triiodothyronine increased 4 fold from 18E to 20E, and thyroxine increased 3 fold from 16E to 19E. IGF-I and IGF-II peaked at 14E. IGF-I steadily increased above embryonic levels during the three weeks of the post hatch period whereas IGF-II levels steadily declined. These results suggest that IGF-II may be a more important functionary for chick embryonic development than IGF-I, and IGF-I may be more important than IGF-II after hatch. The profile of metabolic hormones in the present study may help support an understanding of significant changes that occur in embryonic development and post-hatch growth in chicks.