EFFECT OF THYROTROPIN-RELEASING-HORMONE, TRIIODOTHYRONINE, AND CHICKEN GROWTH-HORMONE ON PLASMA-CONCENTRATIONS OF THYROXINE, TRIIODOTHYRONINE, GROWTH-HORMONE, AND GROWTH OF LYMPHOID ORGANS AND LEUKOCYTE POPULATIONS IN IMMATURE MALE CHICKENS

One-day-old White Leghorn male chicks were fed different levels of Thyrotropin Releasing Hormone (TRH) (1 and 5 ppm) or Triiodothyronine (T3) (.1 and 1 ppm) for an 8-wk period. In a second experiment, chicken growth hormone (cGH) (10 micrograms/kg of BW) was injected (iv) into different birds daily for 7 days starting at 7 wk of age. Different groups of birds received both T3 (.1 and 1 ppm) and cGH. Serum concentrations of thyroxine (T4), T3, and growth hormone (GH), lymphoid organ weights, total circulating white blood cells (WBC), and differential counts were measured following hormone treatments. It was found that T3, cGH, or a combination of both significantly lowered serum T4 concentrations. Triiodothyronine supplementation at 1 ppm, alone or with cGH significantly increased serum T3 concentrations. Chicken GH with T3 (.1 ppm) significantly increased serum GH concentrations. Thyrotropin releasing hormone supplementation did not affect serum concentrations of either T4, T3, or cGH. Relative bursa weights were greater in chicks that received T3 (1 ppm) or TRH (1 or 5 ppm) but not cGH. Relative spleen weights were enhanced in response to cGH alone or with T3 (1 ppm) but not TRH. Total WBC count was significantly increased in response to T3 (1 ppm). Supplementation of T3 (.1 or 1 ppm), TRH (1 ppm), and the combination of cGH and T3 (1 ppm) significantly increased the percentage of lymphocyte cell population. These results demonstrate the impact of feeding hormones on T3, T4, and cGH concentrations in the serum and suggest the involvement of the above hormones in the growth of lymphoid organs as well as the production of lymphocytes.