THE INFLUENCE OF BOVINE GROWTH-HORMONE AND GROWTH-HORMONE RELEASING-FACTOR ON ACETYL-COA CARBOXYLASE AND FATTY-ACID SYNTHASE IN PRIMIPAROUSHOLSTEIN COWS

Primiparous Holstein cows received recombinant bovine growth hormone ( bGH), bovine growth hormone-releasing factor (bGRF),or no treatment fr om 118 to 181 +/- d. Milk yield was significantly increased with no ch ange in milk fat percentage or composition. The mRNA and protein abund ance of the key lipogenic enzymes acetyl-CoA carboxylase (ACC) and fat ty acid synthase (FAS) were measured in the mammary gland and adipose tissue. We hypothesized that bGH and bGRF treatment would increase the mRNA and protein abundance of ACC and FAS in the mammary gland, with an associated decrease in adipose tissue. Analysis of ACC mRNA and pro tein abundance in the mammary gland revealed that there was no signifi cant influence of either bGH or bGRF treatment. Analysis of FAS mRNA i n mammary gland revealed that both bGH and bGRF significantly increase d the abundance. However, quantitation of FAS protein in the mammary g land revealed that neither treatment resulted in increased abundance. In adipose tissue, the mRNA and protein abundance of both ACC and FAS were significantly reduced. The increased substrate required for incre ased milk fatty acid yield may be provided through redirection of nutr ients to the mammary gland away from adipose tissue and through overal l increased metabolism of the mammary gland. (C) 1998 Elsevier Science Inc. All rights reserved.