Trimethylamine Concentration in the Rumen of Cattle and its Origins

Abstract

Trimethylamine (TMA) concentrations (concns) in the rumen were quanti-tatively determined by a GC with four rumen-fistulated steers which received daily 5kg of lucerne haycube combined with 3.5kg of formula feed (Diet 1), 8kg of lucerne haycube (Diet II) and 8kg of Italian ryegrass wafer (Diet III) each for 10 days. TMA concn in the rumen reached the peak level after 2-3h of feeding and the maximal averaged concns obtained by the feeding of Diets I, II and III were 695, 706 and 418 TMA-Nμg/100ml of rumen juice (RJ), respectively. The TMA-N: NH₃-N ratio was 1:8.6 at the maximal concn of TMA. This fact indicates that TMA is present in the RJ of cattle under con-ventional feeding conditions. When apparent precursors of TMA such as betaine, choline and trimethylamine oxide (TMAO) as well as fish meal, rapeseed meal (RSM) and soybean meal (SBM) were administrated into the rumen of a steer through a rumen fistula, TMA occurred in the rumen. The TMA formation, however, was not observed when casein and urea combined with starch were administrated. Thus, TMA in the rumen is con-cluded to occur mainly by degradation of certain substances, including the above pre-cursors, in the feedstuffs and not to be formed by methylation of ammonia.