Evaluation of a ruminally protected methionine product for lactating dairy cows

In Experiment 1, three ruminally and duodenally cannulated cows were used to assess the extent of ruminal protection and postruminal release of Met from ruminally protected Met using a polyester bag technique. The ruminally protected Met contained 85.1% DL-Met (wt/wt). Ruminal disappearance of Met averaged 5.8, 8.1, 21.8, 37.5, and 87.5% after 3, 6, 12, 24, and 96 h of incubation, respectively. Postruminal disappearance of Met from bags inserted in the duodenum after treatment with pepsin-HCl averaged 63.4, 62.6, 51.6, 43.6, and 8.8% for bags incubated in the rumen for 3, 6, 12, 24, and 96 h, respectively. In Experiment 2, 12 cows were fed either 0 or 20 g/d of ruminally protected Met from 7 to 10 d prepartum until 18 wk postcalving. Cows were fed the same total mixed diet. The DMI; yields of milk, CP, and SNF; and percentages of fat, CP, and SNF in milk were not affected by treatment. However, yields of fat and 3.5% FCM increased when ruminally protected Met was fed. Milk N components were not affected by treatment. Concentrations of Met increased in plasma when ruminally protected Met was fed. The mechanism for the increased production of milk fat and 3.5% FCM when ruminally protected Met was fed is unknown.