Metabolism of Betaine in the Ruminant

Abstract

[1-14C] betaine, [15N] betaine and [methyl-14C] betaine were used in vitro and in vivo studies of betaine metabolism in the rumen. Labeled acetate was recovered when [1-14C] betaine was incubated with buffered rumen contents. [methyl-14C] betaine gave rise to radioactivity in trimethylamine, methane and C02. Betaine appeared to be metabolized more rapidly when incubated with rumen contents obtained from animals fed an all-roughage diet rather than a mixed roughage-grain diet; however, studies with [15 N] betaine indicated that ammonia production from betaine was greater with the mixed diet. When [1-14C] betaine was added to the rumen of a fistulated sheep, the label was found in both rumen and blood acetate and a total of 48.2% of the administered radioactivity was recovered in the expired CO2. The addition of [methyl-14C] betaine to the rumen was followed by a rapid production of 14C-labeled trimethylamine. Radioactivity in the urine amounted to 23.4% of the dose and 71% of that radioactivity could be accounted for as trimethylamine and its N-oxide. Other losses of the methyl label were: expired CO2, 16.4%; rumen methane, 9.9%; and rumen CO2 , .3%. An estimated turnover rate of 45% per hour was measured for the period of most active betaine utilization in the rumen. Possible pathways for betaine metabolism in the rumen are discussed.