Galactopoietic effects of recombinant somatotropin and growth hormone-releasing factor in dairy cows.
Eight Holsteins per group received 12 mg/d of recombinant growth hormone-releasing factor or 29 mg/d of recombinant bST or served as untreated controls for 60 d. Milk yield and composition were measured for 10 d before infusion, during infusion (d 0 to 59), and for 20 d after infusion ended. Compared with controls, bST and growth hormone-releasing factor increased SCM during infusion. The SCM yield of cows treated with growth hormone-releasing factor was greater than that of bST-treated cows during the final 20 d of infusion. Relative to controls, bST and growth hormone-releasing factor increased serum concentrations of somatotropin and IGF-I during infusion. Concentrations of somatotropin and IGF-I in serum of bST- and growth hormone-releasing factor-treated cows did not differ during infusion. In summary, growth hormone-releasing factor increased SCM yield more than bST, despite similar serum concentrations of somatotropin and IGF-I. Thus, the galactopoietic action of growth hormone-releasing factor was not explained solely by elevation of total radioimmunoassayable somatotropin and IGF-I in serum.
Dahl
G E
GE
Department of Animal Science, Michigan State University, East Lansing 48824.
Chapin
L T
LT
Moseley
W M
WM
Tucker
H A
HA
D000818:Animals; D002417:Cattle / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D013006:Growth Hormone / Q000097:blood / Q000494:pharmacology*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007700:Kinetics; D007774:Lactation / Q000187:drug effects*; D011994:Recombinant Proteins / Q000494:pharmacology
D005230:Fatty Acids, Nonesterified; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone