Influence of bovine growth hormone and growth hormone-releasing factor on messenger RNA abundance of lipoprotein lipase and stearoyl-CoA desaturase in the bovine mammary gland and adipose tissue

Our objective was to determine the influence of bovine growth hormone (bGH) and bovine growth hormone-releasing factor (bGRF) administration on the mR NA abundance of lipoprotein lipase (LpL) and stearoyl-CoA desaturase (SCD). Primiparous Holstein cows received. bGH, bGRF, or no treatment from 118 to 181 +/- 1 d postpartum. We hypothesized that bGH and bGRF treatment would increase the mRNA abundance of both SCD and LpL in the mammary gland with a corresponding reduction in adipose tissue. Milk yield significantly increa sed but milk fat percentage did not change as a result of bGH or bGRF treat ment. Short-, medium-, and long-chain fatty acid concentrations in milk wer e not affected by either bGH or bGRF treatments, with the exception of a mo dest, but significant, increase in C16:1 and C18:1 following bGH treatment. Analysis was conducted on the genes encoding LPL (E.C. 3.3.1.34), a key en zyme involved in the uptake of fatty acids into tissues, and SCD (E.C. 1.14 .99.5), which is the enzyme responsible for introducing Delta 9 double bond s in fatty acids of 16 and 18 carbons in length. In adipose tissue, treatme nt with bGH and bGRF reduced the mRNA abundance of LpL to 14.6 and 25.7% re spectively, of that observed for control animals. Similarly, these treatmen ts reduced the SCD mRNA abundance to undetectable levels in adipose tissue. In mammary gland, bGH and bGRF had no significant impact on LpL mRNA abund ance. Bovine GH did not significantly affect SCD mRNA abundance in the mamm ary gland, and bGRF reduced SCD mRNA abundance. From this study to examine the role of bGH and bGRF on the expression of the genes encoding these key lipogenic enzymes in cattle, we conclude that the increased substrate requi red for enhanced milk fatty acid yield may have been provided through redir ection of nutrients to the mammary gland away from adipose tissue and throu gh overall increased metabolism in the mammary gland.