Total and individual amino acids in strained ruminal liquor from cows fed graded amounts of urea.

Total and individual amino acids were determined in samples of strained ruminal liquor from an experiment in which cows were fed a low protein, high concentrate diet supplemented with graded amounts of urea to elicit a range of ruminal ammonia concentrations. Total amino acids plateaued beyond 2% crude protein from urea and 6.5 mM ruminal ammonia. There was a negative quadratic relationship between concentrations of total amino acids and ammonia with total amino acids maximized at 16.2 mM ammonia. Individual amino acids followed trends similar to that of total amino acids, increasing with dietary urea and ruminal ammonia before plateauing or declining slightly. Contribution to the animal's amino acid requirements from passage of free amino acids in strained ruminal liquor were estimated for three essential amino acids. Based on mean concentration in strained ruminal liquor, liquid turnover rates, and requirements for gain, 7, 16, and 12% of the requirements for methonine, lysine, and threonine may be contributed from passage of ruminal free amino acids.