Plasma concentrations of insulin like growth factors (IGF-)I and IGF-II in dwarf and normal chickens of high and low weight selected lines.

Plasma concentrations of hormones related to growth and development were determined in normal and in dwarf chickens from lines selected for high or low juvenile body weight. In young (51 days of age) chickens, plasma concentrations of insulin like growth factor (IGF-) I were lower in the low than high weight lines and were reduced in dwarf compared with in normal birds. However, no differences in plasma concentrations of IGF-I were observed between adults from low and high growth lines. Plasma concentrations of IGF-II were lower in the low growth line irrespective of age and, also were reduced in dwarf birds. No line differences were observed with either thyroxine (T4) or triiodothyronine (T3). Dwarf chickens had reduced plasma concentrations of T3 but not T4. Correlations between and amongst hormone concentrations and body weights were observed. The present studies provide evidence for a role of IGF-I, IGF-II and T3 in poultry growth.