Effectiveness of Rumen-Protected Methionine for Delivering Methionine Postruminally in Dairy Cows

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Abstract
A methionine preparation encapsulated for protection from degradation in the rumen was studied in vitro and in vivo to determine: its effectiveness in delivering methionine postruminally; and its effect on the concentration of blood-plasma methionine and other amino acids and on production by dairy cows. Rumen-protected methionine was 94% stable in pH 5.4 buffer, which simulated ruminal pH, and it released 94% of methionine in pH 2.9 buffer, wihch simulated abomasal pH. Holstein cows (25) in early lactation were used to evaluate this preparation in vivo. Cows were assigned randomly to receive 1 of the following 5 concentrations of rumen-protected methionine: 0, 157, 315, 472 and 630 mg/kg feed as fed. This trial consisted of a 3-wk base period (no rumen-protected methionine fed) followed by a 3-wk dose period (treatment diets fed). Methionine concentrations in blood plasma for the 5 dietary rumen-protected methionine concentrations were (.mu.g/ml): 3.4, 4.0, 4.8, 5.1 and 5.3. Corresponding concentrations for the base period were (.mu.g/ml): 3.2, 3.4, 3.5, 3.4 and 3.4. The linear increase of methionine in plasma indicates this preparation delivered methionine postruminally. There was no effect on concentration of other plasma amino acids. The cows receiving rumen-protected methionine consumed more feed and gained more weight than did the control cows. Other production measures were unaffected.