TEMPORAL SECRETORY PATTERNS OF GROWTH-HORMONE IN MALE MEAT-TYPE CHICKENS OF LINES SELECTED FOR BODY-WEIGHT GAIN OR FOOD CONVERSION

1. The pronounced episodic release of chicken growth hormone (cGH) in male broiler chicks, as well as its peak interval of about 90 min was confirmed in this study. 2. Lines selected for 6-week body weight (GL line) or for food conversion between 3 and 6 weeks of age (FC line) not only differ in the selection criteria but also in percentage abdominal fat. 3. The overall mean plasma GH concentration was higher in the FC line in both experiments, and this was only caused by peak amplitudes which were almost twice as high as in the FC line. Peak intervals were identical in both selected lines. 4. These observations suggest that decreased abdominal fat and increased protein efficiency may be genetically linked to increased plasma GH peak amplitude. This, and earlier observations on the effectiveness of pulsatile administration of cGH on the growth of broilers suggest that the biological function of GH may depend on its secretory pattern rather than its mean concentration in plasma.