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Estimation of Methionine Synthesis in Intact Cows after Administering Sulfide-³⁵S^{1, 2,}

Department of Dairy Science, Ohio Agricultural Research and Development Center, Wooster, Ohio

A study was made to determine the amount of methionine synthesized in the rumen. Sodium or barium sulfide-³⁵S was given orally as a source of sulfur for ruminal methionine synthesis in cows adjusted to controlled levels of constant feed intake. The 24-hour turnover of methionine was determined by adding to the daily rations increments of fish meal, a protein source found to be 91% undegraded in passing through the rumen. The logarithm of the decline in specific activity of methionine in milk protein closely fitted a linear regression indicating that methionine was behaving as a single pool undergoing simple dilution. It was therefore possible to estimate the pool size of the net methionine available for use in milk synthesis. Net methionine available was resolved into synthesized and food methionine by regression procedures. Daily methionine synthesis in cows eating alfalfa varied between 31 and 59 mg/kg of body weight.

² This investigation was supported in part by Public Health Service Research Grant no. EF 302 from the Division of Environmental Engineering and Food Protection.

Manuscript received 22 September 1966.