Bacterial D-alanine concentrations as a marker of bacterial nitrogen in the gastrointestinal tract of pigs and cows

Abstract

D-alanine (DAL) has been successfully used as a marker of bacterial nitrogen (N) in the small intestine of cows. This study compares DAL contents of intestinal bacteria in digesta of cows and pigs with respect to diet and sampling site. In isolated ileal bacteria of pigs a DAL/N ratio (41.72 ± 3.19 mg/g, <I>n</I> = 18) was found, which was not different from that in rumen bacteria (40.11 ± 1.95 mg/g, <I>n</I> = 18) but higher than in duodenal bacteria of cows (38.09 ± 2.09 mg/g, <I>n</I> = 18, <I>P</I> < 0.001). The DAL/N ratio in ileal bacteria of pigs was independent of the diet (<I>P</I> = 0.38) but it tended to be affected by the animal (<I>P</I> = 0.095). In bacterial preparations derived from cows, the DAL/N ratio depended on the diet (<I>P</I> = 0.04) and the site of sampling (<I>P</I> = 0.004). Our findings indicate that a general value for DAL/N ratio in pig or cow intestinal contents to calculate bacterial N should not be used.