TY - JOUR
T1 - Influence of peptides and amino acids on fermentation rate and de novo synthesis of amino acids by mixed micro-organisms from the sheep rumen
AU - Atasoglu, Cengiz
AU - Valdés, Carmen
AU - Newbold, C. J.
AU - Wallace, R. John
N1 - Atasoglu, C., Valdés, C., Newbold, C. J., Wallace, R. J. (1999). Influence of peptides and amino acids on fermentation rate and de novo synthesis of amino acids by mixed micro-organisms from the sheep rumen. British Journal of Nutrition, 81 (4), 307-314.
PY - 1999/4
Y1 - 1999/4
N2 - The influence of different N sources on fermentation rate and de nova amino acid synthesis by rumen micro-organisms was investigated in vitro using rumen fluid taken from four sheep receiving a mixed diet comprising (g/kg DM): grass hay 500, barley 299.5, molasses 100, fish meal 91, minerals and vitamins 9.5. Pancreatic casein hydrolysate (P; comprising mainly peptides with some free amino acids; 10 g/l), free amino acids (AA; casein acid hydrolysate + added cysteine and tryptophan; 10 g/l), or a mixture of L-proline, glycine, L-valine and L-threonine (M; 0.83 g/l each) were added to diluted(1:3, v/v), strained rumen fluid along with (NH4Cl)-N-15(A; 1.33 g/l) and 6.7 g/l of a mixture of starch, cellobiose and xylose (1 : 1 : 1, by weight). P and AA, but not M, stimulated net gas production after 4 and 8 h incubation (P <0.05) in comparison with A alone. P increased microbial-protein synthesis (P <0.05) compared with the other treatments. All of the microbial-N formed after 10 h was synthesized de nova from (NH3)-N-15 in treatment A, and the addition of pre-formed amino acids decreased the proportion to 0.37, 0.55, and 0.86 for P, AA, and M respectively. De novo synthesis of amino acids (0.29, 0.42 and 0.69 respectively) was lower than cell-N. Enrichment of alanine, glutamate and aspartate was slightly higher than that of other amino acids, while enrichment in proline was much lower, such that 0.83-0.95 of all proline incorporated into particulate matter was derived from pre-formed proline. Glycine, methionine, lysine, valine and threonine tended to be less enriched than other amino acids. The form in which the amino acids were supplied, as P or AA, had little influence on the pattern of denovo synthesis. When the concentration of peptides was decreased, the proportion of microbial-N formed from NH3 increased, so that at an initial concentration of 1 g peptides/l, similar to the highest reported ruminal peptide concentrations, 0.68 of cell-N was formed from NH3. Decreasing the NH3 concentration at 1.0 g peptides/l caused proportionate decreases in the fraction of cell-N derived from NH3, from 0.81 at 0.53 g NH3-N/l to 0.40 at 0.19 g NH3-N/l. It was concluded that different individual amino acids are synthesized de novo to different extents by mixed rumen micro-organisms when pre-formed amino acids are present, and that the source of N used for synthesis of cell-N and amino acids depends on the respective concentrations of the different N sources available; however, supplementing only with amino acids whose synthesis is lowest when pre-formed amino acids are present does not stimulate fermentation or microbial growth.
AB - The influence of different N sources on fermentation rate and de nova amino acid synthesis by rumen micro-organisms was investigated in vitro using rumen fluid taken from four sheep receiving a mixed diet comprising (g/kg DM): grass hay 500, barley 299.5, molasses 100, fish meal 91, minerals and vitamins 9.5. Pancreatic casein hydrolysate (P; comprising mainly peptides with some free amino acids; 10 g/l), free amino acids (AA; casein acid hydrolysate + added cysteine and tryptophan; 10 g/l), or a mixture of L-proline, glycine, L-valine and L-threonine (M; 0.83 g/l each) were added to diluted(1:3, v/v), strained rumen fluid along with (NH4Cl)-N-15(A; 1.33 g/l) and 6.7 g/l of a mixture of starch, cellobiose and xylose (1 : 1 : 1, by weight). P and AA, but not M, stimulated net gas production after 4 and 8 h incubation (P <0.05) in comparison with A alone. P increased microbial-protein synthesis (P <0.05) compared with the other treatments. All of the microbial-N formed after 10 h was synthesized de nova from (NH3)-N-15 in treatment A, and the addition of pre-formed amino acids decreased the proportion to 0.37, 0.55, and 0.86 for P, AA, and M respectively. De novo synthesis of amino acids (0.29, 0.42 and 0.69 respectively) was lower than cell-N. Enrichment of alanine, glutamate and aspartate was slightly higher than that of other amino acids, while enrichment in proline was much lower, such that 0.83-0.95 of all proline incorporated into particulate matter was derived from pre-formed proline. Glycine, methionine, lysine, valine and threonine tended to be less enriched than other amino acids. The form in which the amino acids were supplied, as P or AA, had little influence on the pattern of denovo synthesis. When the concentration of peptides was decreased, the proportion of microbial-N formed from NH3 increased, so that at an initial concentration of 1 g peptides/l, similar to the highest reported ruminal peptide concentrations, 0.68 of cell-N was formed from NH3. Decreasing the NH3 concentration at 1.0 g peptides/l caused proportionate decreases in the fraction of cell-N derived from NH3, from 0.81 at 0.53 g NH3-N/l to 0.40 at 0.19 g NH3-N/l. It was concluded that different individual amino acids are synthesized de novo to different extents by mixed rumen micro-organisms when pre-formed amino acids are present, and that the source of N used for synthesis of cell-N and amino acids depends on the respective concentrations of the different N sources available; however, supplementing only with amino acids whose synthesis is lowest when pre-formed amino acids are present does not stimulate fermentation or microbial growth.
KW - YIELDS
KW - BACTERIA
KW - PROTEIN
KW - rumen
KW - ammonia
KW - UREA-CONTAINING DIETS
KW - GROWTH RATES
KW - AMMONIA
KW - protein synthesis
KW - IN-VITRO
KW - amino acid
KW - NITROGEN-METABOLISM
KW - PURIFIED DIET
KW - STEERS
KW - sheep
UR - http://hdl.handle.net/2160/9384
U2 - 10.1017/S0007114599000550
DO - 10.1017/S0007114599000550
M3 - Article
SN - 0007-1145
VL - 81
SP - 307
EP - 314
JO - British Journal of Nutrition
JF - British Journal of Nutrition
IS - 4
ER -