Effect of diet and bacterial pellet on the bacterial N and amino acid flows from single-flow continuous-culture fermenters

Six single-flow continuous-culture fermenters fed two different diets and with inoculum from goats or sheep were used in two 11-d incubation periods to investigate the effects of using different bacterial pellets on the estimation of bacterial N and amino acid (AA) flows. Diet AH consisted of 993 g of alfalfa hay and 7 g of a vitamin-mineral mixture per kg, and diet OLSUP was composed of 671 g of olive leaves, 228 g of barley grains, 94 g of faba beans and 7 g of a vitamin-mineral mixture per kg. On the last day of each run, solid(SAB) and liquid(LAB) associated bacteria were isolated from the content of each fermenter. Bacterial N and AA flows were estimated using SAB or LAB composition. Pellets isolated from AH-fed fermenters presented greater (P < 0.001) contents of purine bases (PB) either adenine or guanine, as well as greater PB:N ratios. Significant effects of the diet (P < 0.05) were found on 14 of 17 AA. LAB presented greater (P < 0.05) N and PB concentrations compared to SAB, although no differences (P = 0.266) were detected for PB:N ratio. The AA profile of SAB differed (P < 0.05) from LAB in 5 and 9 of 17 AA for diets AH and OLSUP, respectively, but the numerical differences were, in general, small. Estimates of bacterial N flow were not affected (P = 0.125) by the type of pellet used for calculations, but the flow of bacterial AA, estimated with LAB, was greater (P < 0.05) for 7 and 11 of 17 AA for AH and OLSUP diets, respectively, compared to that calculated with SAB. There were diet x bacterial pellet interactions (P < 0.05) for 6 AA, indicating that the bacterial pellet chosen to estimate the AA flow of bacterial origin could affect the interpretation of differences between diets.