Ruminal degradability, intestinal disappearance, and plasma methionine response of rumen-protected methionine in dairy cows

Bioavailability of Met from a rumen-protected Met product was evaluated in two experiments using three ruminally and duodenally cannulated lactating ( experiment 1) and nonlactating (experiment 2)dairy cows. In the first exper iment, the ruminal in situ and mobile bag technique was used to assess rumi nal degradability and intestinal disappearance of Met from the protected Me t product. Effective ruminal degradability of Met at a ruminal outflow rate of 0.11/h was 21.7%. Combining effective ruminal degradability with intest inal digestibility yielded an estimate of Met availability of 25%. In the s econd experiment, designed as a 3 x 3 Latin square, Met availability was as sessed by determining the response of plasma Met to supplementation of the protected Met product relative to that of duodenally administered Met. The periods were 1 wk with cows fed a meal containing 0, 20, or 63 g of protect ed Met on d 1 and infused intraduodenally with 10.7 g of Met on d 4. Blood was collected at various times relative to the time of oral dosing and the commencement of the duodenal infusion. Plasma Met response measured as area under the curve increased linearly with increasing protected Met. The resp onse of plasma Met increased by 33 and 65.5% of the control values for 20 a nd 63 g of protected Met, respectively. Intestinal bioavailability of Met i n the protected Met product ranged from 22 to 34%.