Submitted to: Journal Of Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 6, 1999
Publication Date: N/A
Interpretive Summary: Thyroid hormones are involved in many aspects of metabolism in turkeys. It is well- documented that hatchability of turkey embryos is dependent on plasma thyroxine concentrations. This study was conducted to examine the genetic effect of selection for either growth or egg production on turkey embryo thyroid hormone levels. Also, the effect of dietary iodide on embryo hatchability and hormone levels was determined. The results of this study suggest that differences embryo thyroid activity exist between different genetic lines of turkey. Thyroid differences may be related to hatching survival of embryos based on genetically determined thyroid functions. This information will be of interest to scientists as will as turkey producers.
Thyroid hormone secretion increases in turkey embryos during hatching. The purpose of the present study was to determine the effects of genetic state and maternal dietary iodide on embryonic plasma thyroid hormone concentrations in turkeys selected for growth (F) or egg production (E) compared with their corresponding randombred controls (RBC2 and RBC1). Hatchability of eggs produced by the E line has improved following genetic selection compared with its control line (RBC1) whereas hatchability of the F line has declined. Half of each line was fed 4 ppm supplemental iodide to form a factorial arrangement of lines and diets. Dietary iodide had no effect on plasma levels of triiodothyronine (T3) in F or RBC2 hens, but the RBC2 hens had consistently higher plasma thyroxine across a laying cycle and resultant T3 to T4 ratios were greater in RBC2. Conversely, selection of egg production has resulted in no change in plasma T4. Feeding iodide to E and RBC1 hens resulted in significant increases in T3:T4 ratios in E hens while the converse was true for RBC1 hens. Hatchability of eggs from hens fed increased iodide decreased in all lines. The E prepipping embryos had greater T4 and T3 concentrations than the RBC1 embryos, but at hatching only T3 was elevated. The F embryos at internal pipping and hatching had significantly lower T4 concentrations than did RBC2 embryos and elevated at prepipping. The results of these experiments suggest differences exist in embryonic thyroid