Amino acid content and profile of protozoal and bacterial fractions isolated from ruminal contents of lactating dairy cows fed diets differing in nitrogen supplementation

Four cannulated dairy cows were used in a 4 x 4 Latin square experiment to compare amino acid (AA) content and profile of liquid-associated protozoa (LAP), liquid-associated bacteria (LAB) and solid-adherent bacteria (SAB). Cows were fed grass silage supplemented with one of four concentrate mixtures: (1) barley/oats; (2) barley/oats + 1% urea; (3) barley/oats + 12% soybean meal; or (4) barley:oats + 12% soybean meal + 1% urea. The AA content (g AA-N 100 g(-1) of microbial N) in the LAP was 16% higher (P < 0.05) than in the bacteria, and their AA profile differed for 16 AA out of the 18 studied. The SAB contained 20% more (P < 0.05) AA than the LAB, and their AA profile was significantly different for 16 AA. The composition of the diet slightly affected the AA concentrations of leucine, phenylalanine, glutamate, tyrosine and lysine. Protozoal AA content and profile showed no diurnal variation.