INFLUENCE OF DUODENAL INFUSION OF BETAINE OR CHOLINE ON BLOOD METABOLITES AND DUODENAL ELECTRICAL-ACTIVITY IN FRIESIAN CALVES

Four, 4-week old Friesian calves (BW = 50 +/- 3 kg), fitted with duode nal, portal and jugular catheters and duodenal electrodes, were used t o study the metabolism of duodenally infused betaine (Bet) or choline (Chol) and their effects on blood sulphur amino acids and duodenal myo electrical migrating complexes (MMC). Animals were fed milk replacer a t 5 % BW twice daily, but were starved overnight prior to the experime ntal procedure. Animals received a saline infusion for 2 h at l ml/min followed by a 1 h infusion of 1.2 or 3.6 mmol of either Bet or Chol. Infusion of saline was continued for another 2 h after the cessation o f the amino acid infusion. Duodenal MMC were measured with a computer- based data acquisition system (MacLab, ADI, Australia). There were no differences in measured blood metabolites between the jugular and port al vein; therefore, only average values were presented. Plasma Met con centrations increased from 20 mu M, 20 min after initiating Bet infusi on, whereas a lower dose of Chol decreased plasma Met and a higher one had no effect. The highest plasma methionine (Met) concentration (29 mu M) occurred 45 min after the onset of the Bet infusion (1.2 mmol). Compared to the 3.6 mmol Bet infusion, the intraduodenal infusion of 1 2 mmol of Bet resulted in a greater area (P < 0.001) under the plasma Met concentration curve (281.6 v. 73.3 mmol). A similar pattern was o bserved for plasma cystine concentrations. Infusion of Bet or Chol did not change the duration of MMC but Bet increased the number of spikes during the phase of low spiking activity (37.5 v. 14.6 pre-infusion, spikes/min; P < 0.01). Chol had the same effect but only after the inf usion ceased (29.3 v. 11.5 spikes/min; P < 0.01). The velocity of migr ation of regular spiking activity (RSA; related to digesta transport) increased as a result of infusion (16.4 pre-infusion v. 31.3 Bet, 25.2 Chol cm/min; P < 0.01). Chol caused an immediate increase in the velo city of migration of RSA, whereas with the Bet infusion an increase wa s observed after cessation of infusion. Increased concentrations of su lphur amino acids during Bet infusion could indicate that labile methy l groups may be limited in calves. Postruminal Bet and Chol supplement ation may cause a decrease in nutrient absorption in the small intesti ne by increasing digesta transport.