THE EFFECT OF ORALLY-ADMINISTERED THYROTROPIN-RELEASING-HORMONE ON GROWTH AND CARCASS CHARACTERISTICS OF 7-WEEK-OLD TO 10-WEEK-OLD BROILERS

In contrast to some earlier studies with young broiler chickens, sever al recent studies have shown growth responses to exogenous growth horm one (GH) administration in broiler chickens of advanced age (Vasilatos -Younken et al., 1988; Scanes et al., 1990). It was therefore of inter est to determine whether intermittent feeding of thyrotropin-releasing hormone (TRH), a known GH secretagogue, would elevate plasma GH of 7- to 10-wk-old broilers and alter their growth characteristics. Four re plicate pens of 15 males and four pens of 15 females 7 to 10 wk of age were given access to feed containing 3.5 mg/kg of TRH for four 2-h pe riods each 24 h with 4-h periods of feed removal between. Control grou ps either were fed the basal ration on the same intermittent schedule or had continuous access to it. Growth hormone concentrations, measure d 45 to 75 min after the start of TRH feeding periods, were significan tly elevated in males on the lst day of the experiment and after 7, 14 , and 21 days when they were 7, 8, 9, and 10 wk of age, respectively. Concentrations in females were elevated on the lst day of treatment, b ut not thereafter. Treatment with TRH had no effect on BW or relative gain of males at any time. It significantly increased relative gain of females during the lst wk, but not thereafter. There were no treatmen t effects on 10-wk shank length, Pectoralis major weight, Gastrocnemiu s weight, or liver weight in either sex, but the percentage fat pad of males fed TRH was lower than that of controls fed intermittently.