Influence of methionine derivatives on effluent flow of methionine from continuous culture of ruminal bacteria

Two separate studies were conducted using a continuous culture fermenter system to determine effects of supplementing D,L-methionine and various methionine derivatives on degradation of methionine by ruminal bacteria. A basal diet containing 20% alfalfa hay, 20% corn silage and 60% grain mix (DM basis) was provided at a rate of 75 g DM/d per fermenter and served as an unsupplemented control in both experiments. In Exp. 1, methionine sources included D,L-methionine, D,L-methionine hydantoic acid, D,L-methionine hydantoin, N-acetyl-D,L-methionine, methylthio-isobutyric acid, methylthio-propionic acid and D,L-methionine sulfoxide. These sources were added directly to fermenters twice daily and supplied an equivalent of 98 mg/d D,L-methionine (.13% of diet DM) and 21 mg/d S. Effluent methionine flow from fermenters was higher (P less than .05) with diets supplemented with D,L-methionine hydantoic acid (245 mg/d), D,L-methionine hydantoin (245 mg/d) and N-acetyl-D,L-methionine (270 mg/d) than with control (211 mg/d) or D,L-methionine (211 mg/d) treatments, indicating a lower ruminal bacterial degradation of these methionine derivatives. There were no major effects on bacterial fermentation due to methionine supplementation or source. In Exp. 2, methionine sources included D,L-methionine, methionine hydroxy analog and N-hydroxymethyl-D,L-methionine; these were mixed with the basal diet to provide an equivalent of 250 mg/d D,L-methionine (.33% of diet DM). Sodium sulfate was added to the control diet to attain equal S (54 mg/d) levels across treatments. Flow of methionine was not affected (P greater than .05) by methionine supplementation, indicating extensive degradation of all three methionine sources by ruminal bacteria.