Sixty-day infusions of somatotropin-releasing factor stimulate milk production in dairy cows.
Twenty-four Holstein cows were infused intravenously with sterile water (placebo) or 1,3, or 12 mg of recombinant bovine somatotropin-releasing factor 1-45-homoserine lactone/d for 60 d. Relative to placebo (22.8 kg/d), 3 and 12 mg of somatotropin-releasing factor increased yield of milk to 28.8 and 33.3 kg/d during infusion. At 1 mg of somatotropin-releasing factor, milk averaged 27.5 kg/d during infusion but was increased above placebo only through 39 d. After infusion of 12 mg somatotropin-releasing factor ended, milk (26.4 kg/d) remained above placebo amounts (20.6 kg/d) for 15 d. Three and 12 mg of somatotropin-releasing factor increased serum somatotropin from .7 (placebo) to 8.2 and 10.3 ng/ml when averaged across 1, 30, and 59 d, whereas 1 mg increased somatotropin to 5.8 ng/ml after 1 d but had no effect at 30 or 59 d. Within 17 h of cessation of somatotropin-releasing factor infusion, serum concentrations of somatotropin were similar across all groups. On d 59, 3 and 12 mg infusions increased insulin-like growth factor I from 115.8 (placebo) to 204.7 and 261.4 ng/ml of serum. We conclude that somatotropin-releasing factor increased serum concentrations of somatotropin and milk yield in a dose-dependent manner for at least 60 d. Also galactopoietic effects of somatotropin-releasing factor persisted for 15 d independent of increased concentrations of somatotropin in serum following withdrawal of somatotropin-releasing factor.
Dahl
G E
GE
Department of Animal Science, Michigan State University, East Lansing 48824.
Chapin
L T
LT
Zinn
S A
SA
Moseley
W M
WM
Schwartz
T R
TR
Tucker
H A
HA
D000818:Animals; D002417:Cattle / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D013006:Growth Hormone / Q000097:blood; D013007:Growth Hormone-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D007262:Infusions, Intravenous / Q000662:veterinary; D007774:Lactation / Q000187:drug effects*; D008892:Milk / Q000737:chemistry / Q000378:metabolism; D011897:Random Allocation; D011994:Recombinant Proteins / Q000008:administration & dosage / Q000494:pharmacology
D011994:Recombinant Proteins; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone