Fatty acid elongation and Delta9 desaturation: effects of diet and genetic background in cattle

Abstract

Fatty acid elongase and stearoyl-CoA desaturase are measurable enzymes involved in converting saturated fatty acids (SFA) to monounsaturated fatty acids (MUFA). To better understand the effects of diet, diet regimen, genetics, and season on these enzyme systems we conducted three experiments. 1) The influence of feed on lipogenesis and enzyme activity: Elongase and desaturase activity in liver and elongase and desaturase activity, cellularity, and lipogenesis in subcutaneous adipose tissue were quantitated in Brangus steers fed either 0% whole cottonseed (WCS) (n = 6) or 30% WCS (n =6). De novo lipogenesis (14C-acetate incorporation per 100 mg adipose tissue) was significantly lower in steers fed 30% WCS (122.1 nmol vs 171.4 nmol vs., p @ .03). Elongase activity correlated with de novo lipogenesis. 2) Influence of feeding regimen on elongase and desaturase activities in subcutaneous and intramuscular adipose tissue: Brangus steers created by nuclear transfer cloning were established as calf-fed (n = 5) or yearling-fed (n = 4) cohorts and assayed at a common fatness (1.2 cm subcutaneous fat thickness). Elongase activity was greater in yearling-fed than calf-fed steers in the intramuscular depot (98.28 pmol vs. 40.93 pmol, P = .02). Desaturase activity was higher in calf-fed than yearling-fed steers in both depots, though not significantly (P = .07). Elongase activity did not correlate with de novo lipogenesis. 3) Influence of genetic composition and season on subcutaneous and intramuscular adipose tissue: We measured elongase and desaturase activities in subcutaneous and intramuscular adipose tissue in steers that were either 3/4 Angus (n = 58) or 3/4 Brahman (n = 39). Elongase activity was greater during Fall in subcutaneous adipose of both breeds (P = .03). Desaturase activity was enhanced during Summer, but was significant only in the intramuscular adipose tissue (P = .005). The MUFA:SFA ratio was higher in Summer than Fall for both breeds (P = .04) and was higher in 3/4 Brahman than 3/4 Angus (P = .01). Results from these experiments support the hypothesis that desaturase is a marker for cell proliferation and differentiation in bovine adipose tissue. Elongase activity, however, does not consistently correlate with lipogenesis or differentiation.