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ARTICLE |
1 Bovine Functional Genomics Laboratory, Animal and Natural Resources Institute, Agricultural Research Service, United States Department of Agriculture, Beltsville, MD 20705-2350
2 Department of Animal Science, University of Kentucky, Lexington 40546
3 Department of Animal Sciences and Nutrition Program, Washington State University, Pullman 99164
* To whom correspondence should be addressed. E-mail: rbaldwin{at}anri.barc.usda.gov.
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Abstract |
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To determine response to alteration in site and form of carbohydrate delivery to the digestive tract, in vitro rates of lipogenesis and lipolysis in mesenteric (MESA), omental (OMA) and subcutaneous (SQA) adipose depots were compared. Forty crossbred beef steers (243 ± 2 kg BW) were fed 161 (LI) or 214 (HI) kcal ME/(kg BW0.75·d) or they were fed LI and infused for 35 d into the rumen (R) or abomasum (A) with starch hydrolysate (SH) or into the abomasum with glucose (G). Jugular blood samples were collected, steers were slaughtered, and adipose depots were sampled and prepared for assessment of lipogenesis and lipolysis in vitro. Blood concentrations of glucagon were increased (P = 0.04) in HI compared to LI steers, whereas A-SH tended to increase (P = 0.08) circulating IGF-1 relative to R-SH, and A-G tended to have elevated (P = 0.09) T3 compared with A-SH. Lipolysis as assessed by NEFA release was unaffected by treatment. Glycerol release by the MESA and SQA was increased or tended to be increased (P 
0.08) in HI compared to LI steers. In A-G compared to A-SH steers, glycerol release from OMA increased (P = 0.008) and from SQA tended to be increased (P = 0.08). Acetate incorporation into total neutral lipids (TNL) increased or tended to increase with ME intake and SH infusion (P 0.09) across all depots. Rates of acetate incorporation into fatty acids (FA) also increased or tended to be increased (P 0.1) by SH infusion across all depots, but only SQA was increased with ME intake (HI vs. LI; P = 0.02). Rates of MESA acetate incorporation into FA and TNL were increased (P 0.03) by A-SH compared to R-SH, but site of SH infusion did not affect rates in SQA or OMA. Glucose incorporation into TNL for MESA and SQA increased or tended to be increased (P 0.1) by dietary and infused energy, whereas for OMA tended to be increased (P = 0.1) only by SH infusion. In contrast, glucose incorporation into FA was unaffected by energy supply but tended to be increased (P = 0.07) by SH in MESA and tended to be greater (P = 0.08) for A-G than A-SH in OMA. The general across depot pattern of acetate incorporation rate into FA and TNL was SQA > OMA > MESA whereas, for glucose incorporation, rates across depots were equivalent. This data provides evidence that post-ruminal supply of energy, specifically carbohydrate, stimulates lipogenesis from both acetate and glucose and is more pronounced in abdominal depots relative to the subcutaneous depot.
Key Words: Steers, Carbohydrate, Adipose, Metabolism
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