Influence of orally administered thyrotropin-releasing hormone on plasma growth hormone, thyroid hormones, growth, feed efficiency, and organ weights of broiler chickens.

Thyrotropin-releasing hormone (TRH) was administered continuously or intermittently in the drinking water of male broiler chickens from 2 to 21 days of age. Intermittent administration of TRH was accomplished by giving birds access to the solution for 2 hr, then removing it for 2 hr, with six repetitions of this procedure each 24 hr. The TRH concentration was such that the birds each would ingest 10 to 20 micrograms of the material during each 2-hr period that it was available. Plasma growth hormone (GH) levels were elevated within 30 min after an episode of TRH administration at 2, 7, and 14 days of age but not at 21 days. Continuous administration of TRH had no effect on GH in plasma at any age. Thyroxine concentrations in plasma were increased within 30 min of first exposure to TRH at 2 days of age, but they were unaffected by intermittent episodes of TRH at 7, 14, and 21 days of age. Triiodothyronine concentrations in plasma were unaffected by TRH at any age. Even though intermittent TRH administration elicited significant elevation in plasma GH for at least 14 days of the experiment, it had no effect on body weight, feed consumption, or weight of the gastrocnemius muscle, the pectoralis major muscle, liver, tibia, or abdominal fat pad.