Effect of pattern of administration on the response to exogenous pituitary-derived chicken growth hormone by broiler-strain pullets.

The effect of pulsatile versus continuous intravenous administration of exogenous, pituitary-derived chicken growth hormone (cGH) on growth performance and endocrine/metabolite status of broiler-strain pullets was determined. In a first study, 8-week-old pullets, surgically prepared with intravenous catheters and maintained via a fluid swivel/spring tether/harness system, were administered cGH or vehicle (control) over a 10-min period every 90 min (i.e., 90-min pulse pattern) for 21 consecutive days. Feed intake, body weight gain, and carcass yield and composition were determined in conjunction with plasma concentrations of several hormones and metabolites. In a second study, 8-week-old pullets were intravenously administered cGH or vehicle continuously for 21 consecutive days under the same conditions as for Study I. Pulsatile cGH administration improved feed efficiency (P less than 0.02), increased longitudinal bone growth (P less than 0.02) and mass (P less than 0.01), and reduced abdominal fat pad size (P less than 0.05) and total carcass lipid (P less than 0.09) over the 21-day treatment period in comparison to vehicle infusion. Pulsatile cGH administration also resulted in hepatomegaly, a marked elevation in plasma IGF-I (P less than 0.003) and T3 (P less than 0.005) concentrations, and a reduction in plasma T4 levels (P less than 0.04). In contrast to the above responses to pulsatile cGH, continuous intravenous cGH administration significantly impaired feed efficiency (P less than 0.01) and had no significant effect on abdominal fat pad or liver size or on total carcass lipid, but did result in widening of the epiphyseal growth plate (P less than 0.06) and increased bone mass (P less than 0.01) in comparison to vehicle infused controls. These studies demonstrate that in the broiler chicken, for which endogenous plasma GH concentrations are pulsatile at early ages in conjunction with rapid growth, the pattern of exogenous GH administration is clearly a factor influencing the nature of response to the hormone.