Changes in plasma methionine concentrations after administration of two different doses of rumen protected methionine

Abstract Text: Feeding rumen-protected limiting amino-acids, such as methionine (MET), to dairy cows may allow feeding of diets with lower amounts of crude protein while increasing milk protein and feed efficiency. Information on the changes of circulating MET concentrations after feeding may provide valuable information on both its usage and its metabolism, which could then be used by field nutritionists. The objective of the present experiment was to determine changes in plasma MET concentrations after administration of a single bolus of rumen-protected methionine (RPM). Non-lactating, non-pregnant dairy cows (n=16) weighing 694±16 kg were randomly assigned to three treatments: 1) untreated control (n=4); 2) bolus containing 10g of RPM (Smartamine; 6g of metabolizable MET; n=6); and 3) bolus containing 20g of RPM (Smartamine; 12g of metabolizable MET; n=6). Blood samples were collected at 12h before treatment, immediately before treatment, and at 6, 12, 18, 24, 36 and 48h after treatment. Plasma was assayed for free amino acid by gas chromatography using a commercial kit (EZ:faast™GC-FID Physiological, Phenomenex). Data were analyzed by repeated measures using the MIXED procedure of SAS. Plasma MET concentrations tended to differ among treatments (P=0.08) and were greater for cows receiving the 20g bolus, intermediate for cows receiving the 10g bolus, and least for control cows (peak average 57.5±0.8µM, 26.9±0.2µM, and 20.3±0.2µM, respectively). Before treatment, all cows had low MET concentrations (21.4±0.5µM), and MET concentrations remained low throughout the experimental period in controls. At 12 and 18h, MET concentrations increased (P=0.09)  by 30% in cows receiving the 10g bolus (26.5±0.2µM) compared to control cows (20.3±0.1µM); however, cows receiving the 20g bolus increased more than 100% (50.4±4.1µM) and were greater than either controls (P<0.01) or cows treated with the 10g bolus (P<0.01). By 24 h after treatment, MET concentrations differed among treatments (P<0.001) and were least for controls (22.7±0.1µM), intermediate for cows receiving the 10 g bolus (23.7±0.1µM), and greater for cows receiving the 20 g bolus (29.6±0.1µM). Methionine concentrations did not differ among treatments (P=0.85) at 36 and 48 h. Lysine concentrations did not differ among treatments (P=0.52) and were 143.3±5.2µM, 133.3±5.4µM, and 139.6±6.8µM for controls, cows receiving 10g of RPM, and cows receiving 20g of RPM, respectively. In conclusion, plasma MET concentrations were affected by treatment dose and time after treatment. Time after treatment should be considered when evaluating effectiveness of MET supplementation. Supported by: Hatch project WIS01240 and Adisseo USA, Inc.

Keywords: Methionine, dairy cow, amino-acids