Increases in microbial nitrogen production and efficiency in vitro with three inhibitors of ruminal methanogenesis.

It was hypothesized that the addition of crotonic acid or 3-butenoic acid would relieve constraints in digestibility observed when methane formation is inhibited by lumazine, propynoic acid, or ethyl 2-butynoate. In six incubations, one of the three methanogenesis inhibitors, at three different concentrations, was combined with either crotonic acid or 3-butenoic acid at two different concentrations. A mixture of buffer and ruminal fluid (4:1) was incubated with grass hay in Erlenmeyer flasks for 72 h. Initial concentrations were 0, 0.6, and 1.2 mmol/L for lumazine; 0, 2, and 4 mmol/L for propynoic acid; and 0, 4, and 8 mmol/L for ethyl 2-butynoate. 15Nitrogen (N) incorporation was used as a microbial marker. All three methanogenesis inhibitors decreased proteolysis. Propynoic acid and ethyl 2-butynoate at 8 mmol/L also decreased the digestibility of organic matter and neutral detergent fibre. However, all three inhibitors of methanogenesis increased the production of microbial N through an improvement of synthetic efficiency. Crotonic acid and 3-butenoic acid were generally ineffective in compensating digestibility decreases caused by the inhibitors of methanogenesis. It is of interest to elucidate the mechanisms by which these compounds increased the efficiency of microbial N production. Lumazine and the addition of low levels of ethyl 2-butynoate could potentially benefit animal production by lowering methane emissions, decreasing ruminal proteolysis, and increasing microbial N production without affecting organic matter digestibility.