GALACTOPOIETIC EFFECTS OF A (1-30)NH2 ANALOG OF GROWTH HORMONE-RELEASING FACTOR IN DAIRY-COWS

Two experiments were conducted to determine the galactopoietic effects of an analog of growth hormone-releasing factor. Specific replacement s were made in the AA sequence of growth hormone-releasing factor to p roduce a growth hormone-releasing factor analog with enhanced stabilit y in vivo. In Experiment 1, 24 Holstein cows were infused i.v. with 0, .33, 1, or 3 mg/d of growth hormone-releasing factor analog for 20 d. Infusion of the analog increased mean serum concentrations of somatot ropin, ICE-I, and NEFA. The analog also increased milk yield as much a s 44% relative to that of controls. In Experiment 2, 24 Holstein cows were infused i.v. with 0, .11, .33, or 1 mg/d of analog for 60 d. Infu sion of analog increased serum concentrations of somatotropin, ICE-I, and NEFA in a dose-dependent manner. At 1 mg/d, the analog increased S CM yield 28% throughout the infusion period relative to the 0 mg/d con trols. In summary, a growth hormone-releasing factor analog increased milk yield and serum concentrations of somatotropin and IGF-I. Further more, this galactopoietic activity was mediated through the somatotrop ic axis.