Physiology of turkey embryos during pipping and hatching. IV. Thyroid function in embryos from selected hens

Embryos from turkey hens selected for high and low hatchability were blood sampled at 24, 25, 26, 27, and 28 days of incubation. The plasma was recovered and assayed for thyroxine (T4) and triiodothyronine (T3) to observe differences in plasma T3 and T4 concentrations relative to reduced hatchability. Plasma T3 did not differ significantly between the high and low hatchability groups, but plasma T4 concentrations were significantly greater during pipping at 26 and 27 days of incubation in the high hatchability group than in the low hatchability group. No differences were observed between the T3 and T4 ratios of the high and low hatchability groups. Oxygen consumption was significantly lower in the low hatchability group than in the high hatchability group. The data indicated that hypothyroidism may be a physiological factor limiting hatchability in domestic turkeys.