The effect of feed intake level on splanchnic metabolism in growing beef steers

The effect of feed intake level (.6, 1.0, and 1.6 x maintenance energy and protein requirements, M) on splanchnic (portal-drained viscera [PDV] plus l iver) metabolism was evaluated in six multicatheterized beef steers (398 +/ - 21 kg), using a double 3 x 3 Latin square design. On the last day of each 21-d experimental period, six hourly blood samples were collected from art erial, portal, and hepatic vessels. Due to catheter patency, PDV fluxes wer e measured on five steers, and liver and splanchnic fluxes on four steers. Increasing intake elevated (P < .01) splanchnic release of total (T) amino acids (AA), through increases (P < .01) in PDV release of both essential (E ) and nonessential (NE) AA, in spite of a tendency (P < .20) for increased Liver removal of NEAA. The PDV release of AA N represented 27 and 51% of di gested N for 1.0 and 1.6 x M, respectively. At 1.0 and 1.6 x M, the liver r emoved 34% of total AA released by the PDV. For individual AA, portal flux Of most EAA increased (P < .05) with feed intake, and the increase (P < .10 ) in splanchnic flux was accompanied by increased arterial concentration fo r all EAA except histidine, lysine, and methionine. This suggests that thes e might be limiting AA for this diet. On a net basis, most individual NEAA were released by the PDV except glutamate and glutamine, which were removed by the digestive tract. There was a net removal of NEAA by the liver, exce pt far aspartate and especially glutamate, which were released. Ammonia rel ease by the PDV tended (P < .20) to increase with intake and represented 69 , 53, and 45% of digested N at .6, 1.0, and 1.6 x M, respectively. Urea rem oved by the PDV, unaffected by intake, represented 32, 33, and 21% of the d igested N. Arterial glucose concentration increased linearly (P < .01) with greater intake, whereas net liver and splanchnic glucose release increased in a quadratic (P < .05) manner. Net PDV glucose release represented 26% o f net glucose hepatic release at 1.6 x M. Intake elevated (P < .10) both in sulin and glucagon arterial concentrations, resulting from a larger increme nt of portal release (P < .01) than hepatic removal (P < .05). Intake-based variations in IGF-I and NEFA arterial concentrations (P < .05) were not re lated to changes in splanchnic metabolism. These results clearly show the c rucial role of the splanchnic tissues in regulating the profile and quantit y of AA and concentrations of glucose and pancreatic hormones reaching peri pheral tissues.