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Methionine as a Precursor of Methyl Sulfide in Cows' Milk¹

Department of Dairy and Poultry Science, Kansas State University, Manhattan

ABSTRACT

Lactating cows were fed methionine and sulfur to determine their effect on methyl sulfide (Me₂S) level in milk. Methyl sulfide production from separate in vitro fermentations of methionine, methionine sulfoxide, and methionine sulfone was determined in an attempt to account for decreased Me₂S production following alfalfa hay storage.

Gas chromatographic analysis for Me₂S was performed on milk from six cows fed alfalfa hay alone, alfalfa hay plus 26 g 90% DL-methionine, and alfalfa hay plus 5 g sulfur daily. Methionine yielded more (P < .005) Me₂S in milk than sulfur or hay alone, which were not significantly different from each other.

In vitro fermentation of methionine, methionine sulfoxide, and methionine sulfone each with ground alfalfa and rumen fluid inoculum resulted in more (P < .01) Me₂S from methionine and methionine sulfoxide during the first five hours, with the level of Me₂S from methionine sulfone approaching that from the other amino acids only after six hours of fermentation. Methionine and its derivatives all produced more (P < .01) Me₂S than did the control treatment, ground alfalfa hay with inoculum.

¹ Contribution no. 685, Department of Dairy and Poultry Science, Kansas Agricultural Experiment Station, Manhattan.