Serum concentrations of thyroid hormones during egg laying in two types of Japanese quail (Coturnix coturnix japonica).

In the present investigation a lighter white egg-type (L) and a heavier wild meat-type (M) of female Japanese quails were compared with respect to egg production, body growth, abdominal fat pad, serum thyroxine (T4) and triiodothyronine (T3) concentrations, TRH sensitivity and T4 5'-monodeiodinase activity in liver homogenates. During the investigation period L type layed considerably more eggs and M type was heavier in body weight. Abdominal fat pad in L type quails was significantly higher than in M type ones. L type quails had lower serum T4 and T3 concentrations than M type ones and the liver T4 5'-monodeiodinase activity was higher in M type than in L type quails. Following TRH administration serum T4 and T3 concentrations increase was higher in L type quails than in M type ones. Our results suggest that lower T4 and T3 observed in L type quails reflect a possible metabolic adaptation to egg production. Different activities of 5'-monodeiodinase and of response to TRH may be inherent to these two types of quail.