Kinetics of ruminal degradation of wheat and potato starches in total mixed rations.

Wheat and potato are rich in starch but their starches differ in their rate of ruminal degradation. Kinetics of in sacco disappearance and profiles of ruminal fermentation were studied for these two concentrates in total mixed rations based on grass silage or corn silage. Wheat starch was more rapidly (34%/h) degraded by rumen microorganisms than potato starch (5%/h). The differences in starch degradation in sacco were found again in the VFA concentrations, mainly in grass silage-based diets. Overall ruminal pH, total VFA concentration, and proportions of acetate, propionate, and butyrate are more variable for wheat during the kinetic (amplitude and quickness) than for potato in grass silage-based diets. In these diets, risks of acidosis were more elevated with wheat than with potato but the VFA concentrations were also higher. These differences of fermentation profile were so reduced in corn silage-based diets that, in this case, wheat can be substituted by potato without any effect on digestion and no risk of acidosis.

Variation of proteolytic activity in ewe during in vivo digestion of two pea-based diets differing by their fermentability characteristics.

In order to study the effects of a small difference in starch and nitrogen availability on proteolysis, two different diets were supplied to four ewes fitted with rumen fistulae. They differed in the ratio of fermentable nitrogen over fermentable energy. with 144 g of fermentable nitrogen (FN) per kg of fermentable energy (FE) for diet I and 126 g FN x kg(-1) FE for diet II. The diets were constituted of 700 g hay grass, 200 g ground pea and either 100 g ground wheat (diet I) or 100 g corn starch (diet II). After two weeks of an adapting period to the diets, rumen content was sampled after feeding over time. The rate of disappearance of soluble proteins was 2.5 times higher with diet II and ammonia concentrations were significantly lower (from -28 to -43%) with diet II. Total proteolytic activity, by considering all the bacterial compartments, was significantly higher with diet II (+40 EU/mL x h(-1)): changes in the total proteolytic activity in the particulate and the liquid phases of the rumen could explain the difference observed between the two diets. Moreover, with diet II, exopeptidase activities increased more in the liquid phase, especially leucine aminopeptidase and Dipeptidyl peptidase I (DPP-I), and the diversity of endopeptidase activities increased in the particulate phase. These two facts could account for the higher total proteolytic activity in the rumen content with diet II.

Effects of ammonia and amino acids on the growth and proteolytic activity of three species of rumen bacteria: Prevotella albensis, Butyrivibrio fibrisolvens, and Streptococcus bovis.

The addition of increasing physiological concentrations of ammonia or amino acids had distinct effects on the growth and proteolytic activity of Streptococcus bovis JB1, Prevotella albensis, and Butyrivibrio fibrisolvens DSM3071. The growth of S. bovis and B. fibrisolvens was enhanced by NH(3) and AA, and that of P. albensis was reduced compared with a control with protein as the sole source of nitrogen. The proteolytic activity of S. bovis and P. albensis was reduced, but that of B. fibrisolvens was improved. NH(3) seemed to act mainly on the cell-associated fraction of the proteolytic activity, while the action of AA was not specific. In the rumen the proteolytic activity of S. bovis and P. albensis would be optimal at low concentrations of NH(3) or AA (<0.05 and <0.27 g/L respectively). In contrast, B. fibrisolvens would need higher concentrations (0.5 g/L of NH(3) or 2.7 g/L of AA). It can be assumed that these bacteria will grow in different ecological niches.

[Degradation and uptake of 14C labeled casein peptides by mixed bacteria of the rumen]. / Dégradation et prélèvement de peptides de caséines marqués au 14C par des bactéries mixtes du rumen.

This work studied the in vitro degradation by mixed rumen bacteria of various 14C-labelled fractions of casein peptides, of known molecular size, added to a total unlabelled casein hydrolysate. Size exclusion HPLC was used in order to segregate the casein peptides according to their molecular weights. Radioactivity associated with the bacteria increased over time. The way 14C was incorporated into the bacteria depended on the size of the labelled peptides initially added. Small peptides (1 to 2 kDa) were very rapidly assimilated, whereas radioactivity coming from larger peptides (5 to 10 kDa) tended to accumulate far more slowly in the bacterial pellet. The disappearance rates of the radioactivity differed between the fractions. The longest peptides disappeared more quickly than the medium-sized ones, which in turn were hydrolysed more rapidly than the smallest ones. Here, the uptake of small peptides seems to be the limiting step of the peptides utilization by bacteria.

In vitro study of molecular weight, hydrophobicity and amino acid composition of peptides during breakdown of a casein hydrolysate by two strains of Prevotella ruminicola.

The molecular weight, amino acid composition and hydrophobicity of the peptide residue produced by hydrolysis of protein by two strains of Prevotella ruminicola (23 and S17/3) were determined. These last two characteristics could play a role in the control of proteolysis. Both strains produced dipeptidyl peptidases (DAP-1) but only P. ruminicola 23 synthesised alanine aminopeptidase. The area of 3-5 kDa peptides decreased, while the peptides directly assimilable by bacteria (0.5-1 kDa and < 0.5 kDa) increased with strain S17/3, but decreased with P. ruminicola 23. The amino acid compositions showed that the proportions of these compounds changed little with time and there was proline enrichment. Similarly, reverse phase HPLC showed no evidence of enrichment of the culture medium by hydrophobic peptides during the growth phase of P. ruminicola. These experiments show that the changes in the various peptide classes resulting from the hydrolysis and uptake of peptides by P. ruminicola differed with time and depended on the strain used. The nature of the enzyme activity and the use of other nitrogen sources may explain the difference between the two strains.

Breakdown of peptides from a casein hydrolysate by rumen bacteria. Simultaneous study of enzyme activities and physicochemical parameters.

The breakdown of a pancreatic hydrolysate of casein (tryptone) by an inoculum of ruminal mixed bacteria was studied in vitro. Peptides were degradated at 33% after 5 h. The dipeptidyl aminopeptidase type 1 (DAP-1), exoaminopeptidase and leucine aminopeptidase (LAP) like activities were measured using, respectively, Gly-Arg-MNA, Ala-pNa and Leu-pNA as substrates. While the total proteolytic activity remained stable throughout peptide breakdown, the DAP-1 already present at the beginning of fermentation increased until two times its early activity. This peptidase activity is a major index for the presence of Prevotella ruminicola. A peak of exoaminopeptidase and LAP activities were observed at 3 h incubation. This latter activity, which was associated with the production of lactate after 3 h, suggested that Streptococcus bovis was present in the environment. With the use of high-performance size exclusion chromatography (HPSEC), the size of the peptides during their breakdown could be measured, showing that high molecular weight peptides (4 to 2 kDa) were apparently more rapidly broken down to the profit of small-sized peptides (< 0.5 kDa), which increased. These degradation abilities were closely linked to DAP-1 activity. Separation of tryptone peptides by reverse-phase high-performance liquid chromatography (HPLC) showed that more hydrophilic peptides disappeared than hydrophobic peptides. Moreover, a few peaks eluting for one in the hydrophilic area and for the others in the hydrophobic area resisted the bacterial breakdown. In contrast, amino acid profiles indicated that hydrophobic amino acids were not taken up significantly faster than the hydrophobic amino acids by mixed ruminal bacterial.

Interactions between proteolytic and cellulolytic rumen bacteria during hydrolysis of plant cell wall protein.

During the degradation of the plant cell wall protein of dried alfalfa, interactions may occur between hydrolytic activities of cellulolytic (Ruminococcus albus or Fibrobacter succinogenes) and proteolytic (Prevotella ruminicola or Butyrivibrio fibrisolvens) bacteria. In vitro the hydrolysis of these protein compounds begins after the depolymerization of the cell wall polysaccharides has started. Maximal degradation of cell wall protein of dried alfalfa (37.2%) was obtained with cocultures of Prevotella ruminicola and Ruminococcus albus.

[Explanation and prediction of the kinetics of degradation in a Rusitec fermentor of nitrogenous vegetable matter after cell wall fractionation]. / Explication et prévision des cinétiques de dégradation en Rusitec des matières azotées végétales à partir d'un fractionnement des parois.

The relation between nitrogen solubility in Van Soest detergents and in vitro nitrogen degradation was studied on 11 substrates with degradation process calculations in digestive trials and an artificial semi-continuous flow (Rusitec) rumen. The kinetics of plant protein degradation in Rusitec, especially the maximum degradation values, were rather similar to those calculated from literature data obtained in situ. In the exponential model used to describe the protein degradation, the maximum disappearance (a + b) was negatively correlated with the percentage of acid detergent insoluble nitrogen in the Van Soest (ADIN/Total N). In the foods tested, the non degradable fraction corresponds to a quantity which is equivalent to approximately 76% of the ADIN fraction. The instantaneously degraded nitrogen (a) was rather well explained by the percentage of neutral detergent insoluble nitrogen in the Van Soest (NDIN/Total N). The rate of disappearance (c) of the slowly degraded fraction was inversely correlated with the proportion of ADF in the NDF, which demonstrates the latter's resistance to degradation. This type of fractionation could be used in predicting nitrogenous value of feed stuffs for ruminants.

[Comparison of goats and sheep with respect to the ingestion, digestibility and nutritive value of various diets]. / Comparaison des caprins aux ovins quant á l'ingestion, la digestibilité et la valeur alimentaire de diverses rations.

The voluntary food intake, organic matter, crude protein and crude fiber digestibility and nitrogen balance of 23 diets have been measured simultaneously using 5 to 7 wethers and 5 to 7 castrated billy-goats in digestibility trials. The goats ate more than the wethers (58 vs 46 g DM/kg W0.75). The digestibilities obtained for goats were highly correlated with those obtained for wethers, and the mean values were similar in both species: Organic matter: digestion coefficient (CUD)goats = 1.22 CUDwethers -14.5 r = 0.93 Crude protein: digestion coefficient (CUD)goats = 1.07 CUDwethers -4.8 r = 0.94 Crude fiber: digestion coefficient (CUD)goats = 0.56 CUDwethers +29.6 r = 0.78 The mean nitrogen balance for goats (226 mg/kg W0.75) was significantly higher than that of wethers (152 mg/kg W0.75). Based on the regression equations for each species, the calculated efficiency of proteins digestible in the intestine (PDI) was 55 p. 100, the endogenous urinary nitrogen 160 mg/kg W0.75 and the nitrogen maintenance requirement 1.8-1.9 g of PDI/kg W0.75.