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 fur 21 consecutive days under the same conditions as for Study I. Pulsatile cGH administration improved feed efficiency (P < 0.02), increased longitudinal bone growth (P < 0.02) and mass (P < 0.01), and reduced abdominal fat pad size (P < 0.05) and total carcass lipid (P < 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 < 0.003) and T3 (P < 0.005) concentrations, and a reduction in plasma T4 levels (P < 0.04). In contrast to the above responses to pulsatile cGH, continuous intravenous cGH administration significantly impaired feed efficiency (P < 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 < 0.06) and increased bone mass (P < 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.
All Science Journal Classification (ASJC) codes
- Animal Science and Zoology