[Comparison of plasma thyroxin and insulin concentrations between 10-day old layer and broiler chickens]

In this study both sexes of 10 day old layer and broiler chickens were used to investigate plasma circulating concentrations of 3,3'-5-triiodothyronine (T3), thyroxine (T4) and insulin by using the radioimmunoassay (RIA) methods. The results were as follows: serum T3 concentration was higher in broilers than that in layers (P < 0.01), especially a significant difference between male strains was seen in this experiment (P < 0.001), and the levels of plasma insulin was significantly higher in male broilers than that in male layers (P < 0.001), however, no clear differences in plasma T4 was seen between strains and sexes (P > 0.05). In addition, there were sex differences in T3 and insulin levels in layers, that is to say, those in the female layers was higher than those in the male layers, but no clear deifference was seen between sexes in broilers. A significant positive correlation between T3, insulin and their weight gained (P < 0.05). The results suggest that the levels of serum T3 and Insulin may influence the various growth rate during early posthatch development in layers and broilers.