Determination of intestinal disappearance of lysine and methionine derived from ruminally protected lysine and methionine in holstein heifers

In order to estimate the availability of ruminally-protected Lys (RPLys) anti Met (RPMet), quantitative changes of free Lys and Met in the total abomasal outflow and feces were determined in three Holstein heifers with a T-shaped duodenal cannula. RPLys was prepared by coating Lys with fat and RPMet with a pH-sensitive polymer. RPLys and RPMet containing 30 g of each amino acid were supplied together to heifers, and total abomasal outflow was collected hourly from the T-shaped duodenal cannula for a 48 h period. Collected abomasal outflows were fractionated into liquid and solid phases to measure free Lys and Met concentration. At 2 wk after total abomasal outflow sampling, heifers were supplied RPLys and RPMet together again, and total feces were collected every 12 h for a 3 d period to estimate excreted RPLys and RPMet in feces. The amounts of Lys and Met recovered from the liquid fractions of abomasal outflow were estimated to be 23.9±8.3% and 68.6±3.6% (p=0.008) of RPLys and RPMet ingested, respectively. Final intestinal disappearances of Lys and Met were estimated to be 49.5±2.6% and 78.2%±6.5% (p=0.015) of ingested RPLys and RPMet, respectively.