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

A methionine preparation encapsulated for protection from degradation in the rumen was studied in vitro and in vivo to determine: a) its effectiveness in delivering methionine postruminally; and b) its effect on the concentration of bloodplasma methionine and other amino acids and on production by dairy cows. Rumenprotected methionine was 94% stable in pH 5.4 buffer, which simulated ruminal pH, and it released 94% of methionine in pH 2.9 buffer, which simulated abomasal pH. Twenty-five Holstein cows in early lactation were used to evaluate this preparation in vivo. Cows were assigned randomly to receive one of the following five concentrations of tureen-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 five dietary rumen-protected methionine concentrations were (/lg/ml): 3.4, 4.0, 4.8, 5.1, and 5.3. Corresponding concentrations for the base period were (/lg/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 Received May 24, 1983. gained more weight than did the control cows. Other production measures were unaffected.