INFLUENCE OF TRIIODOTHYRONINE AND GROWTH-HORMONE ON GROWTH OF DWARF AND NORMAL CHICKENS - INTERACTIONS OF HORMONES AND GENOTYPE

1. The effects of dietary triiodothyronine (T3), injections of a preparation of growth hormone (GH) (purified from chicken pituitary tissue) and their combination on growth were investigated in three lines of chickens. The three lines were the Cornell K strain (K) (a Single Comb White Leghorn strain), the Cornell K strain hemizygous for the sex-linked dwarfing gene (SLD), and the Cornell K strain homozygous recessive for the autosomal dwarfing gene (ADW). 2. A dietary T3 treatment by genotype interaction was observed. Dietary T3 (0.1 ppm) decreased growth in the K line, tended to decrease growth in the ADW line while it tended to increase growth in the SLD line. 3. Chicken growth hormone (100 .mu.g/kg body wt) alone did not affect growth in any of the lines studied. There was, however, a GH treatment by T3 treatment interaction. Chicken GH overcame the growth depressing effects of T3 in the K and ADW lines while it tended to promote growth in T3 treated SLD birds. 4. Drawf (SLD) chickens had higher basal circulating GH concentrations, lower circulating immunoreactive somatomedin C concentrations, and lower circulating T3 concentrations than the K or ADW chickens.