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Factors Affecting Small Intestinal Carbohydrate Assimilation in Beef Cattle
D.L. Harmon, K.R. McLeod
Department of Animal and Food Sciences
The complexity of ruminant digestion makes it diffcult to determine how dietary ingredients are utilized. This project evaluates nutrient utilization in the animal and by the animal to determine how growth and nutrient utilization interact.
2010 Project Description
We have previously shown that in ruminant calves, glucagon-like peptide-2 (GLP-2) increased small intestinal mass and epithelial mass, villus height, crypt depth, and bromodeoxyuridine (BrdU) labeling in the small intestine without affecting total body mass. The gastrointestinal tract uses amino acids (AA) as an energy source and for protein synthesis. Thus, intestinal growth caused by GLP-2 would likely also alter portal drained viscera (PDV) utilization of AA.
Furthermore, previous research has demonstrated that GLP-2 increases PDV glucose utilization in parenterally-fed piglets, but no information is known in ruminants, which often differ in their regulation and utilization of glucose compared to non-ruminants. Thus, this experiment sought to examine the effects of exogenously-administered GLP-2 on blood AA concentrations and fluxes across the PDV and utilization of glucose by the PDV.
Eight weaned Holstein calves with catheters in the carotid artery, portal vein, and mesenteric vein were paired by age and randomly assigned to treatment: Control (0.5% bovine serum albumin [BSA] in saline; n = 4) or GLP-2 (50 microgram/kg BW bovine GLP-2 in BSA; n = 4). Intake was 2.75% of BW (DM-basis). Treatments were injected subcutaneously every 12 h for 10 d. On day 10, after a 12 h fast to avoid prandial effects on blood flow, calves were continuously infused with para-aminohippurate and [U-13C] glucose to measure portal blood flow and PDV utilization of glucose, respectively. Blood samples were taken every 15 min for 150 min. Plasma was analyzed for para-aminohippurate, for total free AA, and for [U-13C] glucose enrichment. Net PDV flux was calculated as portal plasma flow x (portal - arterial nutrient concentration), with positive values indicating net release and negative values indicating net uptake. Data were analyzed using the MIXED procedure of SAS with treatment as a fixed effect and block as a random effect.
Treatment with GLP-2 for 10 d reduced (P < 0.05) arterial concentrations of the essential AA Leu, Lys, Phe, and Val, and the non-essential AA Gln, Ala, Asn, and Pro. Likewise, 10-d treatment with GLP-2 reduced net PDV release of the essential AA Arg, Ile, Leu, Lys, and Phe, and the non-essential AA Ala, Asn, Asp, Gly, Pro, and Ser. Moreover, negative correlations were found between small intestinal growth measures and arterial AA concentrations and PDV flux.
These results suggest GLP-2 increased growth and resulted in greater sequestration of AA in the PDV, perhaps for protein synthesis. Glutamate and Gln are used for gut energy metabolism and growth, including synthesis of other AA such as Arg, Pro, ornithine, and citrulline. Arterial Gln concentrations were 23% lower with GLP-2 treatment and net PDV uptake of Gln was unchanged; thus, the net PDV extraction of Gln was greater after GLP-2 (0.20 vs. 0.10, P < 0.0001). Greater arterial Gln extraction and reduced PDV ornithine flux may have contributed to the increased citrulline export from the gut and likely resulted in greater renal conversion of citrulline to Arg, and thus greater Arg concentrations in GLP-2-treated calves.
Despite greater Arg concentrations, PDV Arg release was reduced, suggesting PDV retention, perhaps to support small intestinal mucosal growth. Despite changes in AA metabolism, whole body glucose irreversible loss (GIL) did not differ between treatments (117.4 mmol/h). Glucose utilization by the PDV and non-PDV tissues was 0.41 and 0.63, respectively, of GIL and was not affected by treatment. Flux of AA across the PDV is affected by GLP-2, potentially by increased small intestinal epithelial growth and thus energy and AA requirements of this tissue.
Increased PDV extraction of Gln and alterations in PDV metabolism of Arg, ornithine, and citrulline support the concept that intestine-specific AA metabolism is affected by GLP-2. However, unchanged glucose metabolism suggests GLP-2 effects on PDV glucose metabolism in ruminants are more transient or less significant than for non-ruminants.
Taylor-Edwards,C.C., D.G. Burrin, N.B. Kristensen, K.R. McLeod, and D.L. Harmon. 2010. Glucagon-like peptide-2 (GLP-2) alters amino acid fluxes across the portal-drained viscera of ruminant calves. In: Energy and protein metabolism and nutrition EAAP publ. No. 127 G. M. Crovetto (Ed.). pp. 199-200.
Taylor-Edwards,C.C., D.G. Burrin, K.R. McLeod, J.J. Holst, and D.L. Harmon. 2010. Glucagon-like peptide-2 (GLP-2) increases small intestinal blood flow and mucosal growth in ruminating calves. J. Dairy Sci. (In Press).
Taylor-Edwards,C.C., D.G. Burrin, J.C. Matthews, K.R. McLeod, J.J. Holst, and D.L. Harmon. 2010. Expression of proglucagon and glucagon-like peptide-2 (GLP-2) receptor mRNA in the ruminant gastrointestinal tract and the influence of energy intake. Dom. Anim. Endo. 29:181-193.
Riddell, J. B., D. L. Harmon, E.S. Vanzant, and K. R. McLeod. 2010. Addition of a Bacillus based probiotic to the diet of preruminant calves: Influence on growth, health, and blood parameters. Intern. J. Appl. Res. Vet. Med. 8:78-85.
Foote, A.P., J. L. Klotz, D. L. Harmon, L. P. Bush, and J. R. Strickland. 2010. Ergot alkaloids induce vasoconstriction of bovine foregut vasculature. J. Anim. Sci. 88: (E Suppl. 2) 701.
Koontz, A.F., L. P. Bush, J. L. Klotz, K. R. McLeod, F. N. Schrick, and D. L. Harmon. 2010. Development of a fescue toxicosis model using a fescue seed extract. J. Anim. Sci. 88: (E Suppl. 2) 704.
Taylor-Edwards, C., D. G. Burrin, K. R. McLeod, and D. L. Harmon. 2010. SS-ASAS Emerging Scholar Award: Distribution and role of glucagon-like peptide-2 in cattle. J. Anim. Sci. 88: (E Suppl. 2) 26.
Xu, M., M. Rinker, K.R. McLeod, D. L. Harmon. 2010. Yucca schidigera extract decreases in vitro methane production in a variety of forages and diets. Anim. Feed Sci. Technol. 159:18-26.
Koontz,A.F., S.W. El-Kadi, D.L. Harmon, E.S. Vanzant, J.C. Matthews, J.A. Boling, and K.R. McLeod. 2010. Effect of ractopamine on whole body and splanchnic energy metabolism in Holstein steers. Can. J. Anim. Sci. 90:77-85.
Liao, S. F., D. L. Harmon, E. S. Vanzant, K. R. McLeod, J. A. Boling, and J. C. Matthews. 2010. The small intestinal epithelia of beef steers differentially express sugar transporter mrna in response to abomasal vs ruminal infusion of starch hydrolysate. Journal of Animal Science 88:306-314.
Speight, S.M. and D.L. Harmon. 2010. Batch culture evaluation of carbohydrase inhibitors to moderate rumen fermentation. Anim. Feed Sci. Technol. 155:156-162.
Kristensen, N.B., M. Engbaek, M. Vestergaard and D. L. Harmon. 2010. Technical Note: Ruminal cannulation technique in young Holstein calves; Effects of cannulation on feed intake, body weight gain, and ruminal development at six weeks of age. J. Dairy Sci. 93:737-742.