Comparison of Growth Hormone-Releasing Factor and Somatotropin: Lipid and Glucose Metabolism in Dairy Cows

Abstract

Lactating, primiparous Holstein cows were continuously infused for 63 d with either recombinant growth hormone-releasing factor or recombinant bST or were not infused (control). The releasing factor and bST treatments reduced fat synthesis from acetate and lipoprotein lipase activity in omental adipose tissue. Also, both treatments increased hormone-sensitive lipase activity per gram of adipose tissue and reduced fatty acid esterification per milligram of protein in adipose tissue. Protein concentration in adipose tissue with both treatments was greater than that of the control, although the protein concentration was less in adipose tissue from cows treated with the releasing factor than from those treated with bST. In mammary tissue, releasing factor increased fat synthesis from acetate more than did bST treatment, but percentages of fat or short-chain fatty acids in milk were not different between treatments, nor were differences significant between treatments and control for fatty acid esterification or lipoprotein lipase activity in mammary tissue or gluconeogenesis and fatty acid esterification in liver. We conclude that protein concentration was lower in omental adipose tissue of cows treated with releasing factor than that in tissue of cows treated with bST, although both treatments similarly suppressed synthesis of fat from acetate and activity of lipoprotein lipase.