Influence of duodenal infusion of L-methionine and L-methionine-dl-sulfoxide on amino acid concentration and duodenal electrical activity in Friesian calves

Four, 28-day-old Friesian calves (50 ± 3 kg) fitted with duodenal, jugular catheters and duodenal electrodes were used to study absorption of duodenally infused L-methionine (Met) and L-methionine sulfoxide (MSO) and their effect on duodenal motor migrating complexes (MMC). Animals were fed milk replacer at 5% BW twice daily, but were starved overnight prior to experimental procedure. Animals received saline infusion for 2 h at 1 ml min^-1 prior to a 1-h infusion of 3.6 mmol of either Met or MSO. Infusion of saline was continued for another 2 h after cessation of amino acid infusion. Duodenal MMC were measured with the computer-based data acquisition system (MacLab, ADI, Australia). Initial plasma concentrations of Met were similar for both Met or MSO (19 μM) infusion. Plasma Met concentrations increased 20 min after initiating Met infusion. The highest plasma Met concentration (62 μM) occurred 15 min after Met infusion was ceased. Plasma MSO concentrations increased 40 min after the start of MSO infusion. The highest plasma MSO concentration occurred 45 min after cessation of MSO infusion (25 μM). No change in plasma Met concentration (P > 0.1) occurred with MSO infusion. Absorption of MSO was 52% that of Met. Met did not change the duration of MMC but reduced the number of spikes during the phase of irregular spiking activity (305.5 vs 660.3 spikes min^-1 MSO; P < 0.05). MSO prolonged the duration of irregular spiking activity (30.2 vs 22.3 min Met; P < 0.05). The velocity of migration of regular spiking activity increased as a result of Met infusion (39.3 vs 21.2 cm min^-1 MSO; P < 0.001). Lack of change in Met concentration during MSO infusion indicates very little, if any, reduction of MSO in calves. Met at high concentrations may limit the absorption of nutrients through increased passage rate and decreased electrical activity during the absorption phase of MMC.