Studies on methionine derivatives as possible sources of protected methionine in ruminant rations

Metabolism of DL-methionine and methionine analogs by rumen microorganisms

Rates of degradation of DL-methionine and a number of methionine derivatives by rumen microorganisms were studied in vitro. Methionine hydroxy analog, the ammonium salt, and the amide derivative of methionine hydroxy analog were degraded more slowly than was methionine. Methyl and ethyl esters of methionine hydroxy analog were rapidly converted to methionine hydroxy analog, which was then degraded. Whole rumen contents were separated into protozoal and bacterial fractions, and rates of disappearance of [14C]carboxyl-labeled methionine and methionine hydroxy analog were determined. Disappearance of the label tended to be slower in the bacterial fraction; however, incorporation into cellular material tended to be higher for the bacterial than for the protozoal fraction. Disappearance of labeled methionine hydroxy analog was slower than labeled methionine in all fractions. Addition of unlabeled methionine inhibited disappearance of labeled methionine hydroxy analog, but unlabeled methionine hydroxy analog did not affect disappearance of labeled methionine. The effect of either Na2SO4, methionine, or methionine hydroxy analog on neutral detergent fiber digestion was related to amount of sulfur in the medium and not source of sulfur.

Plasma amino acids and milk protein production by cows fed rumen-protected methionine and lysine

Eighteen Holstein cows in midlactation were used to study the effectiveness of encapsulated rumen-protected methionine and rumen-protected lysine to deliver methionine and lysine postruminally. The experimental design was a 2 X 2 factorial, a center point, and a control treatment run in a partially balanced, incomplete block design. Treatments were administered over three periods of 3 wk. Cows were fed a blended diet consisting of corn silage, corn, and soybean meal supplemented with five different amounts of rumen-protected methionine and lysine. The amounts of DL-methionine and L-lysine (g/d), respectively, supplied from the encapsulated rumen-protected preparations for the six treatments were 1) 0, 0; 2) 10.40, 18.00; 3) 4.52, 7.82; 4) 16.28, 7.82; 5) 16.28, 28.18; and 6) 4.52, 28.18. In vitro results indicate that amino acids in both of the encapsulated preparations were 94% stable at a pH (5.4), which simulated the rumen, and 94% released at a pH (2.9), which simulated the abomasal environment. A linear increase of plasma methionine and lysine was observed as the amount of methionine and lysine supplied postruminally increased. The concentrations (microgram/ml) of methionine and lysine in plasma for the six treatments were 1) 2.47, 9.05; 2) 3.73, 11.59; 3) 3.60, 11.86; 4) 6.09, 10.45; 5) 5.28, 13.43; and 6) 3.33, 13.27. Rumen-protected lysine increased feed intake, milk yield, and 4% fat-corrected milk production within the surface treatments but had no effect when compared with the unsupplemented control treatment. Rumen-protected methionine and lysine increased production of milk protein. Lysine appeared to improve the utilization of methionine.