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US Department of Agriculture, Beltsville, MD 20705 and Clay Center, NE 68933
Abstract
Two experiments were conducted to measure the effect of level of feed intake on net amino acid absorption by portal-drained viscera of six beef heifers with catheters in a mesenteric vein, portal vein and iliac artery (Exp. 1) and to evaluate intrajugular infusion of insulin or glucose on amino acid uptake by hind half of four beef steers with catheters in posterior aorta and vena cava (Exp. 2). Experiment 1 was a replicated 3 x 3 Latin square design. Treatments were calculated intakes of 84, 157 or 225 kcal metabolizable energy (ME)/kg.75 live weight. Treatments in Exp. 2 were control (no infusion), insulin infusion (1.4 IU/min for 90 min) and glucose infusion (2.5 mmol/min for 90 min) in that order. Mean live weight of animals ± SE was 295 ± 4 kg (Exp. 1) and 345 ± 15 kg (Exp. 2). The diet used in both experiments was pelleted, 85% concentrate (2.9 Meal ME/kg dry matter). Blood flow (BF) was measured by dilution of a primed, continuous infusion of para-aminohippuric acid into the mesenteric vein (Exp. 1) or the posterior aorta (Exp. 2). Net uptake or absorpion was the product of BF times portal-arterial (Exp. 1) or arteriovenous (Exp. 2) differences in amino acid concentrations in blood. Increased feed intake caused linear (P<.05) increases in net absorption of several amino acids, including lysine, methionine, leucine and valine (Exp. 1). Feed intake did not affect (P
.05) net absorption of glutamate or glutamine. Net absorption of these two amino acids was negative, indicating their use as metabolic fuel by portal-drained viscera. Infusion of insulin or glucose (Exp. 2) did not affect (P>.05) uptake of amino acids measured, but arterial concentrations of amino acids except histidine were lower (P<.05) during infusion of insulin or glucose than during control. Combination and extrapolation of data from these experiments indicate that about one-half of protein deposition in beef steers fed a high concentrate diet is in the hind half.
1 Mention of a trade name, proprietary product, or specific equipment does not constitute a guarantee or warranty by the USDA and does not imply its approval to the exclusion of other products that may be suitable.
2 Present address: 1011 West 2nd Street, Hastings, NE 68901.
3 The authors thank Animal Operations Staff under the direction of R. Sigurdson and J. Grinstead for care and feeding of the animals, B. Stroud and his staff for assistance with surgery of the heifers and R. Mlejnek, B. Lee, J. Whitt and E. Zetina for their able laboratory work.
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