Degradation and outflow of amino acids from the rumen of sheep.

1. In hay-fed, cannulated sheep the apparent degradation in and outflow from the rumen were determined for graded doses of mixtures of the amino acids lysine, threonine and methionine, administered intraruminally and using polyethylene glycol (PEG) as a liquid marker. The doses ranged between 2.5 and 15 g for each amino acid in the mixtures. 2. Relative rate of apparent degradation in the first 4 h was highest for lysine, and lowest for methionine. The apparent degradation in 24 h was highest for lysine and lowest for threonine. Conversely the fraction flowing out of the rumen in intact form in 24 h was highest for threonine and lowest for lysine. Rates of apparent degradation as well as outflow were dose-dependent. 3. The validity of the estimated outflow of amino acids from the rumen was corroborated by measurements of concentrations of the amino acids in duodenal contents and in blood plasma which were also dose-dependent. 4. It was concluded that part of the requirement for the essential amino acids threonine and methionine may be met, even when these amino acids are delivered in unprotected form, given as a feed supplement.