Direct microscopic examination of the rumen and its contents shows microbial populations largely attached to feed particles in the digesta. Most feeds contain a surface layer that is resistant to attachment and therefore to digestion. Infiltration of these recalcitrant epidermal layers through damage sites or through focused enzymatic attack is essential for initiation of the digestive process. Proliferation of primary colonizing cells produces glycocalyx-enclosed microcolonies. Secondary colonizers from the ruminal fluid associate with microcolonies, resulting in the formation of multispecies microbial biofilms. These metabolically related organisms associate with their preferred substrates and produce the myriad of enzymes necessary for the digestion of chemically and structurally complex plant tissues. Upon accessing the internal, enzyme-susceptible tissues, microbial "digestive consortia" attach to a variety of nutrients, including protein, cellulose, and starch and digest insoluble feed materials from the inside out. Substances that prevent microbial attachment or promote detachment (e.g., condensed tannins, methylcellulose) can completely inhibit cellulose digestion. As the microbial consortium matures and adapts to a particular type of feed, it becomes inherently stable and its participant microorganisms are notoriously difficult to manipulate due to the impenetrable nature of biofilms. Properties of feed that place constraints on microbial attachment and biofilm formation can have a profound effect on both the rate and extent of feed digestion in the rumen. Developments in feed processing (i.e., chemical and physical), plant breeding, and genetic engineering (both of ruminal microorganisms and plants) that overcome these constraints through the promotion of microbial attachment and biofilm formation could substantially benefit ruminant production.
Sainfoin leaf condensed tannins inhibited growth and protease activity in Butyrivibriofibrisolvens A38 and Streptococcus bovis 45S1 but had little effect on Prevotella ruminicola B14 or Ruminobacter amylophilus WP225. Tannins bound to cell coat polymers in all strains. implicated the cell wall as a target of tannin toxicity. Morphological changes in B. fibrisolvens and S. bovis Condensed tannins (CTs) are generally regarded as antinutritional for ruminants because of depression of feed intake and dry matter digestibility (13, 24), but their capacity to precipitate proteins reversibly at rumen pH may be nutritionally beneficial (14, 15, 20). When CT-containing herbage is masticated, insoluble CT-protein complexes are formed; these are stable over the pH range 3.5 to 7.0 but dissociate in the abomasum and anterior duodenum (11, 16). This protects the protein from microbial hydrolysis and deamination in the rumen and increases the proportion of plant amino acids available for postruminal absorption. Furthermore, the "bloatsafe" property of pasture legumes such as sainfoin (Onobrychis viciifolia Scop.) and birdsfoot trefoil (Lotus corniculatus L.) is correlated with CT content (14, 15). Most of the proteolytic activity of rumen contents resides with the bacterial fraction (3, 8, 17). Soluble plant proteins typically adsorb to the surface of proteolytic bacteria (21) and are hydrolyzed by constitutively expressed cell coat proteases (12, 22). Our objective was to determine some effects of CTs on growth and proteolysis by four strains of ruminal bacteria representing functionally important proteolytic species (23). The CTs used were purified (2) from leaves of sainfoin (cv. Melrose) and had a high protein-precipitating capacity compared with those of CTs from eight other forage legume sources (9). A single batch of sainfoin leaf CTs was used for all experiments. Effects of CTs on bacterial growth. Butyrivibrio fibrisolvens A38, Prevotella ruminicola B14, Ruminobacter amylophilus WP225, and Streptococcus bovis 45S1 were grown anaerobically (4) in a basal medium, which was the medium of Scott and
. 1999. Effect of sainfoin on in vitro digestion of fresh alfalfa and bloat in steers. Can. J. Anim. Sci. 79: 203-212. The effects of sainfoin (Onobrychis viciifolia) on digestion of alfalfa (Medicago sativa) were investigated in vitro and in vivo. Fresh alfalfa and sainfoin were incubated in an artificial rumen (Rusitec) in ratios of 100:0, 75:25, 50:50, 25:75 and 0:100 (as-fed). Disappearances of dry matter and N from sainfoin were 77 and 65% of those from alfalfa, respectively. Protease and endoglucanase activities, NH 3 -N and methane production declined (P < 0.05) as sainfoin increased. Bacterial numbers and microbial outputs were unchanged (P > 0.05), but cells incorporated more 15 NH 3 N as sainfoin in the diet increased. Chopped leaves (100:0, 95:5 and 90:10 alfalfa:sainfoin) were incubated for 48 h with diluted ruminal fluid containing 0 or 50 mg polyethylene glycol, which binds tannins. Gas and volatile fatty acid productions were similar (P > 0.05) across treatments, but including 10% sainfoin (without polyethylene glycol) reduced (P < 0.05) NH 3 concentrations between 8 and 24 h. Sainfoin tannins reduced degradation of forage protein without affecting the digestibility of the nonprotein fraction. Alfalfa herbage was fed alone or with early-to full-bloom sainfoin herbage (at 10 or 20% of ad libitum alfalfa dry matter intake) or with sainfoin hay or pellets, to eight Jersey steers in crossover trials conducted over 4 yr. Including sainfoin in the diet reduced (P < 0.001) the incidence of bloat by 45 to 93% in 3 of 4 yr, irrespective of the form in which it was supplied. Co-feeding sainfoin can markedly reduce the incidence of bloat in ruminants consuming fresh alfalfa. De l'herbage de sainfoin et de luzerne étaient mis à incuber dans un rumen artificiel (Rusitec) dans les proportions, en l'état, de 100:0, 75:25, 50:50, 25:75 et 0:100. La digestibilité apparente de la m.s. et du N du sainfoin correspondait, respectivement, à 77 % et 65 % des valeurs obtenues pour la luzerne. Les activités de la protéase et de l'endoglucanase de même que la production de N ammoniacal et de méthane diminuaient (P < 0,05) à mesure qu'augmentait la proportion de sainfoin. Par ailleurs, les numérations bactériennes et les apports microbiens restaient inchangés (P > 0,05), mais les cellules microbiennes incorporaient plus de 15 NH 3 -N. Des feuilles hachées (100:0, 95:0 et 90:10 luzerne:sainfoin) étaient mises à incuber pendant 48 h en présence de liquide ruminal dilué contenant 0 ou 50 mg de polyéthylène glycol (PEG), substance qui a pour effet de lier les tanins. Les productions de gaz et d'AGL étaient du même ordre (P > 0,05) d'un traitement à l'autre, mais l'inclusion de 10 % de sainfoin, sans PEG avait pour effet de réduire (P < 0,05) les concentrations de NH 3 entre 8 et 24 h. Les tanins du sainfoin diminuaient la dégradation des protéines du fourrage, sans toutefois altérer la digestibilité de la fraction non protéique. Nous avons aussi servi pendant 4 ans à 8 bouvillons de la luzerne, seule ou combinée, soit à du sain...
To identify simple screening tools for selecting condensed tannin (CT)-containing forages as candidate sources for further study, CT were isolated from nine legumes, and their molecular weights (MW), chromophore production, capacity to precipitate bovine serum albumin (BSA) and Fraction 1 protein (Rubisco) isolated from alfalfa, and inhibition of filter paper digestion were compared. Sources were as follows: leaves of sericea lespedeza (Lespedeza cuneata Dum.-Cours.), crown vetch (Coronilla varia L.), and sainfoin (Onobrychis viciifolia Scop.); stems of hedysarum (Hedysarum alpinum L.); seeds of alfalfa (Medicago sativa L.); and whole plants of birdsfoot trefoil (Lotus corniculatus var. corniculatus L.) and three varieties of big trefoil (Lotus pedunculatus Cav.), viz., Lotus uliginosus Schkuhr, L. uliginosus var. glabriusculus, and L. uliginosus var. villosus. Molecular weights and sizes (degrees of polymerization) of the CT varied considerably within and among plant species. Average MW ranged from 3036 Da (crown vetch) to 7143 Da (lespedeza). All CT exhibited greater capacity (w/w basis) to bind alfalfa Rubisco than BSA. Relative astringencies (microg CT required to precipitate 1 mg protein) against BSA ranged from 262.5 for CT from lespedeza to 435.5 for CT from L. corniculatus, and against Rubisco, from 49.6 (sainfoin) to 108.2 (alfalfa seed). Including CT at 300 microg/ml in cultures of Fibrobacter succinogenes reduced digestion of cellulose filter paper by 19.8% (sainfoin) to 92.4% (crown vetch) and increased the specific activity of cell-associated endoglucanase. There were no correlations between inhibitory effects of CT on filter paper digestion and (1) chromophore formation during CT assay by butanol-HCl, vanillin-HCl, or H2SO4; (2) precipitation of BSA or alfalfa Rubisco; and (3) MW of CT. The most inhibitory CT for cellulose digestion included those with broad and with narrow MW distributions. Sainfoin was the most desirable source of CT, as it had the highest capacity to bind alfalfa protein and was least inhibitory to cellulose digestion by F. succinogenes. This study suggests that these properties are not easily defined via chemical means, and that biological assays using rumen bacteria may help identify those CT with properties of nutritional interest.
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