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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.
2009 Project Description
Glucagon-like peptide-2 (GLP-2) is a 33-amino acid hormone secreted from the gastrointestinal tract that rapidly increases small intestinal blood flow. No experiments have been conducted evaluating the blood flow response to GLP-2 after extended administration, nor have investigations been performed in ruminants.
An experiment was conducted to investigate the role of GLP-2 in the ruminat small intestine. Eight Holstein calves with an ultrasonic flow probe around the superior mesenteric artery (SMA) and catheters in the carotid artery, mesenteric vein, portal vein, and hepatic vein were paired by age and randomly assigned to treatment: vehicle (0.5% BSA in saline; n= 4) or GLP-2 (50 micrograms/kg body weight bovine GLP-2 in vehicle; n= 4). Treatments were administered by subcutaneous injection every 12 h for 10 d. Calves were fed a 50:50 (DM basis) mixture of alfalfa cubes and calf starter at 2.75% of BW in 2 daily meals. A blood flow experiment was conducted on d 0 (Acute) and d 10 (Chronic) of administration and consisted of 3 periods: baseline saline infusion (30 min) to establish baseline blood flow, treatment infusion in which calves were infused with their assigned treatment, either BSA or GLP-2 (1000 pmol/kg/h) for 60 min, and saline infusion (60 min) to observe the recovery of blood flow after treatment infusion. Portal and hepatic blood flows were measured by p-aminohippurate dilution. Results of this experiment were shared as part of a Ph.D. dissertation and they were presented at the national American Society of Animal Science meetings.
The results of the study provided the first evidence of the role of GLP-2 in ruminants. Infusion of GLP-2 increased superior mesenteric artery blood flow to 175% of baseline on d 0 but to only 137% of baseline after 10 days of treatment. Similar trends were observed for portal and hepatic plasma flow. Our results show that GLP-2 increases splanchnic blood flow in ruminants but this response is attenuated after 10-d GLP-2 administration. These results suggest that GLP-2 could modulate nutrient absorption in ruminants through effects on splanchnic blood flow.
Harmon, D.L. 2009. Understanding starch utilization in the small intestine of cattle. Asian-Aust. J. Anim. Sci. 22:915-922.
Taylor-Edwards, C. C., G. Hibbard, S. E. Kitts, K. R. McLeod, D. E. Axe, E. S. Vanzant, N. B. Kristensen, and D. L. Harmon. 2009. Effects of slow-release urea on ruminal digesta characteristics and growth performance in beef steers. J. Anim. Sci. 87:200-208.
Taylor-Edwards, C. C., N.A. Elam, S. E. Kitts, K. R. McLeod, D. E. Axe, E. S. Vanzant, N. B. Kristensen, and D. L. Harmon. 2009. Influence of slow-release urea on nitrogen balance and portal-drained visceral nutrient flux in beef steers. J. Anim. Sci. 209-221.