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

Abstract

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 liver) metabolism was evaluated in six multicatheterized beef steers (398 +/- 27 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 arterial, portal, and hepatic vessels. Due to catheter patency, PDV fluxes were 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 digested N for 1.0 and 1.6 x M, respectively. At 1.0 and 1.6 x M, the liver removed 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 for all EAA except histidine, lysine, and methionine. This suggests that these 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, except for aspartate and especially glutamate, which were released. Ammonia release 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 removed by the PDV, unaffected by intake, represented 32, 33, and 21% of the digested 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% of net glucose hepatic release at 1.6 x M. Intake elevated (P < .10) both insulin and glucagon arterial concentrations, resulting from a larger increment of portal release (P < .01) than hepatic removal (P < .05). Intake-based variations in IGF-I and NEFA arterial concentrations (P < .05) were not related to changes in splanchnic metabolism. These results clearly show the crucial role of the splanchnic tissues in regulating the profile and quantity of AA and concentrations of glucose and pancreatic hormones reaching peripheral tissues.

Effect of intake on whole body plasma amino acid kinetics in sheep

“…These are also sensitive to intake [12,48,49] and these values can increase by approximately 40% when intake is raised from 1 to 2 M [49]. Interestingly, these increases in absolute protein synthesis are associated with greater tissue mass, since the fractional rates of protein synthesis for the splanchnic tissues tend to be insensitive to intake [42,50].…”

“…Non-linear responses in whole body ILR may be due to the impact of other tissues, particularly since the contribution of the hind-quarters (≈ 20%) is less important than that of the splanchnic tissues, for example (30-60% [8,[45][46][47]). These are also sensitive to intake [12,48,49] and these values can increase by approximately 40% when intake is raised from 1 to 2 M [49].…”

“…The advantages include limited surgical invasion, use of longitudinal studies and lower tracer costs compared with the large dose procedure [8,9]. This technique is, however, subject to some limitations [10], especially when a single AA is monitored (such as leucine or phenylalanine [11][12][13]), which may, or may not, be distributed similarly between the different metabolic routes (protein synthesis, oxidation or synthesis of metabolites: [5,9,14]). To date, there have been relatively few comparisons between kinetic data obtained with a number of different AA (e.g.…”

Reviewing the low efficiency of protein utilization in heavy preruminant calves – a reductionist approach

“…This is presumably affected by the relatively high feeding level in the calf study. In pigs and beef steers, increasing the feeding level does not proportionally increase the irreversible loss rate over the portal drained viscera, which implies that portal amino acid recoveries increase with feed intake [78,79]. Secondly, the absence of one poorly recovered indispensable amino acid in milk-fed calves indicates that the amino acid balance is not drastically disturbed by passing the portal drained viscera.…”

Propionate supplementation did not increase whole body glucose turnover in growing lambs fed rye grass

“…The influence of raising the supply of glucose precursors on glucose turnover probably depends on the basal ME level. Lapierre et al [46] showed a curvilinear relationship between net hepatic glucose release and the level of feed intake. Indeed, Seal and Parker [7] and Peiris et al [47] measured only slight increases in the turnover of glucose (+13 and +15%) in steers fed approximately at 920 kJ MEl·d -1 ·kg -0.75 and supplemented with propionate (7.8 and 2.9 mmol·d -1 ·kg BW -1 , respectively).…”