Brigitte Michalet-Doreau

Comparison of methods for predicting digestibility of feeds

Abstract Five techniques were investigated to find a laboratory method for the prediction of the in vivo digestibility of feeds and mixed feeds: two chemical techniques (Weende crude fibre and van Soest methods), one biological technique (in vitro digestibility) and two enzymatic techniques (digestion by pepsin-cellulase, normal or modified (HCl 0.1 N instead of 1 N)). The enzymatic degradability (Method B, HCl 0.1 N) allowed a more accurate prediction of the in vivo organic matter digestibility (OMD) of 24 feeds than the separate data of crude fibre, neutral detergent fibre (NDF), acid detergent fibre (ADF) and acid detergent lignin (ADL) contents or in vitro digestibility. The selected equation obtained with the cellulase method could also be used for feed mixtures.

Influence of genotype and stage of maturity of maize on rate of ruminal starch degradation

Abstract This trial was carried out to determine the influence of genotype and stage of maturity of maize on ruminal starch degradation by an in situ technique. In a first methodological trial, we measured the part of starch lost through the bag pores without being degraded, with two drying methods and four grinding sieves. Starch losses were the lowest for oven-dried at 40°C and 3-mm ground grains. In a second trial, two types of maize differing in the texture of their endosperm, dent or flint, were harvested, respectively, at four and five stages of maturity, between 22 and 78 days after silking. Each maize was characterized by its vitreousness. At maturity, ruminal starch degradability was greater for dent than flint maize (61.3 vs 40.1%) due essentially to a greater rapidly degradable fraction (25.2 vs 15.7%). Dent maize had a lower vitreousness than the flint type, 48.1 vs 72.3%. The differential association between starch granules and protein matrix in each fraction of endosperm alters the accessibility of starch granules to ruminal bacteria. Starch degradation decreased with maturity and this trend was greater for the earlier harvest dates and for flint than dent maize. This decrease came from a lower rapidly degradable starch fraction (51.0 vs 20.4%) and a lower degradation constant rate (14.2 vs 3.8% h −1 ) for the two genotypes. This decrease in starch degradation was related to the increase in the vitreousness of the endosperm with maturity ( r = 0.93). At silage stage (30% dry matter in whole plant), the difference in starch degradation between the two genotypes was high and similar to that determined at maturity of the grain. These results imply that at silage stage ruminal starch escape can be modified by genetic selection.

Predicting in situ degradability of feed proteins in the rumen by two laboratory methods (solubility and enzymatic degradation)

Abstract Two techniques were investigated to find a laboratory method for the prediction of the in situ nitrogen degradation of concentrated feeds: a method using solubility in a buffer (phosphate buffer at pH 6.9) and an enzymatic technique (hydrolysis after 1 h ( DE 1 ) and after 24 h ( DE 24 ) by a protease extracted from Streptomyces griseus in a borate-phosphate buffer at pH 8). Ninety-seven samples of concentrated feeds, representing 26 single feeds and 49 commercial feed mixtures, were studied. Both methods allowed the same precision (residual standard deviation (RSD) ∼ 0.030) if the 26 single feeds were grouped in classes. In contrast, for feed mixtures, the prediction was very precise and much better with the enzymatic method (RSD = 0.025) than with the solubility method (RSD = 0.049). In the French digestible proteins in the intestine (PDI) system, the enzymatic method is used as a laboratory method for nitrogen evaluation.

Validation of in sacco method: influence of sampling site, nylon bag or rumen contents, on fibrolytic activity of solid-associated microorganisms

Three ruminally cannulated cows, fed twice daily with a 70:30 forage:concentrate diet, were used to investigate the differences in fibrolytic activity of solid-associated microorganisms between nylon bags and rumen contents. Two different grass hays (regrowth and late harvested) were incubated in ruminal nylon bags. After 2 h or 23 h incubation time, pH was measured in bags and rumen contents, and enzymes of solid-associated microorganisms were extracted from bag residues and surrounding digesta by grinding, freezing, defrosting and sonication. Xylanase, avicelase, β-D-xylosidase and β-D-glucosidase activities were measured. Activities were lower in bag residues than in rumen digesta, and differences were greater after 2 h than after 23 h incubation time. Causes of these differences are discussed. For each incubation time and each enzyme, the differences in solid-associated microorganisms activities between rumen and bags contents were independent of the quality of hay in the bag. Thus the lower fibrolytic activity inside the bags may account for an underestimation of in vivo ruminal fiber degradation by the in sacco method, but this underestimation may be similar whatever the nature and content of forage cell walls.

Consequences of underfeeding on digestion and absorption in sheep

Abstract The negative relationship between intake and digestibility of an unchanging diet has been widely described. The review of the different processes of ruminal digestion shows that the main cause of the variation in digestibility is the retention time of particles in the rumen. However, most experiments have been carried out at levels of intake higher than maintenance. For this reason, a special attention is paid to experiments carried out at low levels of intake. In these conditions, the response of digestibility to a decrease in intake is variable: it can increase, be stable or decrease. Up till now, it has not been possible to determine the animal or nutritional factors which influence the way of variation, and especially the unexpected decrease in digestibility. However, it has been clearly shown that these decreases are not due to an insufficient retention time of particles in the rumen, or to an insufficient reduction of particle size. Differences in microbial activity have not been exhibited by in situ measurements. It is hypothesised that a reduction of bacterial growth, or of the expression of microbial degradation potential occurs at very low intakes, but mechanisms are still not elucidated. The decrease in weight and oxygen uptake by the digestive tract contributes to the adaptation of animals maintenance requirements. At short term, the proportion of metabolisable energy intake which is recovered in the portal vein remains unchanged when animals are underfed but the supply of absorbable amino acids (AAs) cannot keep up with the gut requirements. The consequences of underfeeding on nutrition and absorption do not differ between small ruminants and cattle.

Postprandial variations in the activity of polysaccharide-degrading enzymes of fluid- and particle-associated ruminal microbial populations

The distribution and specific activities of polysaccharide-degrading enzymes were monitored during the postprandial period in the liquid-associated bacteria (LAB), liquid-associated protozoa (LAP), and solid-associated microbes (SBFP) isolated from ruminal contents of cattle fed a high-cereal diet. Polysaccharide depolymerase activities were highest in the SBFP and the LAP populations. The postprandial variations in the specific activity of amylase were similar within the subpopulations. However, carboxymethylcellulase and xylanase activities increased in the first 5 h after feeding in the LAP, but were highest at the end of the postprandial period in the SBFP. Glycosidases involved in the fermentation of soluble carbohydrates increased significantly immediately after feeding in the liquid-associated microbes. β-d-Glucosidase and β-d-xylosidase were most active in the SBFP and were maximal 23 h after feeding. The activities of the plant cell wall polysaccharide-degrading enzymes and glycosidases in the SBFP were inversely related to ruminal pH; however, the activity of enzymes in the liquid-associated populations were highest in the immediate post-feed period when ruminal pH was lowest.

In situ degradation kinetics of maize hybrid stalks

Abstract An understanding in plant factors influencing digestion kinetics could help develop maize cultivars, thus improving digestibility and consequently the production of ruminants. The stalk fraction of maize hybrids was used to study the cell wall digestion of hybrids varying from the brown midrib-3 (bm3) and their isogeneic normal (N) to normal hybrids. Cell wall constituent contents (NDF, ADF, ADL), soluble carbohydrates (SC), in vitro dry matter digestibility (IVDMD) and ruminal degradation kinetics of the dry matter (DM) and the cell wall (measured as NDF) were determined on stalk samples harvested at silage stage (30–35% DM, whole plant). Six comparative studies of in situ degradability involved 3 comparisons of the bm3 and their N isogeneic hybrids (Ex223, Ex234 and Adonis) and 3 comparisons involving 2 extreme genotypes (DK265 and Stefania): each were compared to the control genotype (Adonis). A comparison of the three sets of N and bm3 hybrids demonstrated that the mutation contained a lower concentration of the cell wall constituents. Hemicellulose rather than cellulose was generally present in lower amounts in the cell walls. Higher SC content and IVDMD were also seen in the bm3 maize. Mean effective degradabilities for both DM (64.4 versus 53.2%) and NDF (36.3 versus 29.5%) were higher ( P

Occurrence of digestive interactions in tree forage-based diets for sheep

The effect of browse level in the diet on the in vivo dry matter digestibility (DMD) in sheep and the DM degradation of peanut hay in the rumen of cattle-fed tree forage-based diets were investigated in order to detect the occurrence of digestive interactions between diet components. Selected browse species Acacia albida pods, Pithecellobium dulce, Adansonia digitata and Calotropis procera leaf samples were collected in the central regions of Senegal, sundried and stored in LNERV animal barns for in vivo trials. Classical in vivo balance trials were performed for each tree forage sample. The proportion of browse in the applied diet varied between 0 and 75% of DM. Regression and difference procedures were both tested to estimate the DMD of the browse component of the diet. DMD capacity in the rumen of three young Gobra bulls fed the browse-based diets was estimated by measurement of the in sacco dry matter degradation profile of a standard sample, peanut hay. For each sample, large variations were observed when the browse DMD was calculated by difference. Both total ration DMD and rumen DM degradation capacity were significantly (p<0.001) influenced by browse level in the diet. However, non-linear response of total diet DMD to increasing levels of browse was observed only in A. digitata and P. dulce indicating occurrence of digestive interactions in those species. Rumen DM degradation capacity varied according to plant species which played a major role in the observed digestion profile. Results suggest that the digestion of tree forages-based diets may be influenced by digestive interactions but the large variations observed in plant species show their importance. Optimal DM degradation occurred at 15–30% of browse level in the diet for both A. albida and A. digitata while for P. dulce it was at 50%. Corresponding browse digestibility was of 50%, 47.1%, 51.3% and 60.7% DM for A. albida, A. digitata, P. dulce and C. procera respectively. Further work using the regression method in a wider range of browse species could help confirm between-species variations.

Effect of Barley Supplement on Microbial Fibrolytic Enzyme Activities and Cell Wall Degradation Rate in the Rumen

Three ruminally cannulated dry cows were used in a Latin square design to investigate the relationship between microbial fibrolytic enzyme activities and in sacco cell wall degradation of two gramineous hays, in which cell wall content ranged from 510 g kg -1 DM for the regrowth to 687 g kg -1 DM for the late harvested hay. Animals were fed twice daily a diet consisting of wheat straw, cocksfoot hay and ground barley in the ratios 10 :90 :0 0 (w/w), 10 : 60 : 30 (w/w) and 10 : 30 : 60 (w/w). For each diet and each hay, the in sacco degradation of cell wall polysaccharides and phenolic acids was determined. After 2 h and 23 h incubation time in the rumen, pH was measured in the bags, and fibrolytic activities (xylanase, avicelase, β-glycosidases) of the microbial population colonising hays in sacco were measured. Supplementation above 30% barley decreased the degradation rate of the cell wall polysaccharides, concomitantly with a decrease in polysaccharidase activities. The decrease in degradation rate was more marked for the regrowth than for the late harvested hay, for hemicelluloses than for cellulose and for ferulic than for p-coumaric acid. These differences did not appear to be related to microbial activities, which were similar between hays and between polysaccharidases, but rather to differences in accessibility of cell wall components to microbial enzymes, related to the composition of the forage and the cell wall architecture.

Effects of amount and availability of starch on amylolytic activity of ruminal solid-associated microorganisms

Three ruminally cannulated dry cows were used in an experiment designed as a Latin square to investigate the effects of amount and availability of starch on the amylolytic activity of ruminal solid-associated microorganisms (SAM). Animals were fed twice daily a diet (7 kg DM day-1) consisting of wheat straw, cocksfoot hay and ground barley in the ratios 10: 90: 0, 10: 60: 30 and 10: 30: 60. Nylon bags containing rapidly (barley) or slowly (maize) degradable cereal grains were incubated in the rumen. Enzymes of the SAM were extracted from rumen contents and bag residues, and amylolytic (amylase and α-D-glucosidase) activities were measured. The in situ degradation of starch was determined. Increasing the level of barley in the diet induced a linear increase in amylase activity of SAM in the rumen contents. In the bags, amylase activity and starch degradation rate were not modified by supplementation. High activity was observed more rapidly in bags containing barley, where starch is rapidly available, than in bags containing maize, where starch is protected by a resistant endosperm. These results suggest that amylolytic activity of SAM may depend on the amount of starch available to microorganisms.