Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 6, 1999
Publication Date: N/A
Interpretive Summary: Nearly one fifth of the life cycle of the turkey is spent as a developing embryo, yet little information is available on how genetic selection for egg production or rapid growth impacts embryo development. The purpose of these experiments were to determine differences in embryo growth of turkey embryos selected for growth and egg production compared to their randombred controls, and to determine the influence of added dietary iodide on embryo growth and glycogen metabolism. Understanding embryonic growth in such selected lines may improve survival rates of embryos. Results of these studies indicated that maternal dietary iodide as well as genetic selection for a single trait such as egg production or body weight may influence embryonic thyroid activity. The influence of dietary iodide differed depending on the genetic background of the embryo. Also, it was evident that added dietary iodide improved muscle growth and glycogen deposition depending on whether the embryo was from hens selected for egg production or were randombred controls. This information will be of interest to both commercial turkey producers as well as other basic scientists.
Embryonic growth of turkeys selected for 16-wk body weight (F) or 180-day egg production (E) was measured and compared to their respective randombred control populations (RBC2 and RBC1). Genetic selection for increased 16-wk body weights resulted in increased egg and embryo weights. Eggs from F weighed 10 g more than those of RBC2, but the poult at hatching was only 8 g heavier. Conductance constants indicated that only .9% of the difference could be accounted for by water vapor loss. Differences in growth of the E line embryos compared to RBC1 occurred entirely following 24d of incubation. Eggs from E hens weighed 15.1 g less than those form RBC1 hens but the RBC1 poults weighed only 7.3 g more at hatching. The conductance constants suggested that only 1.4% of the 2.9% difference could be accounted for by water vapor loss. When iodide was included in the maternal diet, embryonic thyroid function was affected in all lines of turkeys. The added thyroid function seemed to restore muscle growth in the F/RBC2 comparison prior to pipping and in the E/RBC1 comparison at hatching and increased body weights concomitantly in the RBC2 line reduced it in the F line embryo. This observation suggests that the genetic ability of muscle to respond to thyroid hormones is determined early in development and to a greater extent in growth selected than in egg production selected embryos. It was concluded that genetic selection may result in correlated responses in embryonic growth and these growth differences may be mediated in part by maternal and embryonic thyroid functions.