Ruminal Degradation and Outflow of Amino Acids in Cows

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Two rumen- and duodenum-cannulated cows were used to study the disappearance rate, degradation in, and outflow from the rumen of four amino acids administered individually into the rumen at the following dose levels (mmol): lysine 273-547-820, tyrosine 276-496-828, isoleucine 381-762-1143 methionine 335. Calculations were based on the use of PEG (polyethylene glycol, 4000) as liquid marker for determination of the volume and dilution rate of rumen fluid. At the same dry matter intake a comparison was made between the influence of a high-forage and a low-forage diet. At the lowest dose level, the initial rates of disappearance (mmol/l per h) were 0.52 for lysine, 0.48 for tyrosine, 0.55 for isoleucine and 0.58 for methionine. The rates increased with increasing dose levels. The fractions of administered amino acids flowing out of the rumen and the fractions degraded in the rumen were studied over an 11 h period. At the lowest dose level, outflow (mmol/11 h) amounted to 42 and 54 for lysine, 36 and 29 for tyrosine, 93 and 48 for isoleucine, 104 and 75 for methionine on the high and low forage diet, respectively. The corresponding figures for degradation were 232 and 209, 239 and 247, 287 and 333, 226 and 259 mmol/11 h. The fractions of an administered amino acid flowing intact out of the rumen increased, and the fractions degraded in the rumen decreased, with increasing doses.