NET PORTAL FLUX OF METABOLITES FOLLOWING A MEAL IN CALVES FED A GRAIN-RICH DIET SUPPLEMENTED WITH UREA OR MEAT MEAL

The present experiment was carried out to evaluate the effect of prote in supplementation of grain-rich diets on the net absorption of some m etabolites following a meal by calves, estimated from their net portal flux. The study was conducted on eight Holstein male calves with an a verage liveweight of 141 +/- 1.4 kg, fitted with permanent catheters i n a mesenteric vein and in the portal vein and with a temporary cathet er in an auricular artery. The animals were assigned random to two tre atments: T1, hay + concentrate containing urea and T2, hay + concentra te containing meat meal. Portal blood flow (PBF) was estimated by an i ndicator dilution and net metabolites flux was calculated as the diffe rence between venous and arterial concentrations times portal blood fl ow. Feed was offered for 50 min and, immediately after, infusion of th e indicator started and blood samples were taken at 30 min intervals d uring 4 h. Net portal flux of glucose and urea N was negative and simi lar for the two treatments (P > 0.10). Ammonia N, beta-hydroxybutyrate and acetoacetate flux was positive and higher in calves fed diet cont aining urea (P < 0.01, P < 0.07, P < 0.07, respectively). The urea N p ortal flux was quadratically (P < 0.08, r(2) = 0.64) and ammonia N por tal flux cubically (P < 0.06, r(2) = 0.81) related to time after the m eal.