Dam Line and Sire Line Effects on Turkey Embryo Survival and Thyroid Hormone Concentrations at the Plateau Stage in Oxygen Consumption

Inheritance of embryo thyroid function was measured in lines of turkeys. Two lines that had been selected for either increased egg production (E) or increased 16-wk BW (F) and their respective randombred controls (i.e., RBC1 and RBC2) were examined. Reciprocal crosses of dams and sires from each selected line and its randombred control were made to estimate sire line and dam line effects. Orthogonal contrasts were used to determine if the differences found were due to the presence of additive, nonadditive, or maternal, sex-linked, or both, gene effects. With the data involved, sex-linkage and maternal effects could not be separated. Embryo survival was measured for all lines and their reciprocal crosses. Crossing the RBC1 sire and E dam also resulted in better embryo survival and lower death losses at pipping than for the other cross- or purelines. Reciprocal crosses of the F and RBC2 lines showed better total embryo survival, and they survived pipping better than the F or RBC2 purelines. Thyroxine (T₄) and triiodothyronine (T₃) concentrations differed between the reciprocal crosses at external pipping, but the effects were inconsistent for the 2 data sets. Reciprocal tests indicated that maternal, sex-linked, or both, effects were present for T₃ concentrations at internal pipping in the E and RBC1 lines and at external pipping for the F and RBC2 lines. Reciprocal effects were significant for T₄ at internal pipping for both data sets. The RBC1 sire embryos had significantly higher T₃:T₄ ratios than the E line sire embryos at internal and external pipping, and the pureline RBC1 embryos had consistently higher ratios than the pureline E embryos. The differences for the T₃:T₄ ratios between these 2 lines at internal pipping, external pipping, and hatch appeared to be consistently additive in nature, although significant nonadditive or heterotic effects were present for the ratio at external pipping. Similar effects on the T₃:T₄ ratio were observed for the F and RBC2 lines at external pipping.