Reading Assignments. James B. Russell and J.L. Rychlik. 2001. Factors that alter rumen microbial ecology. Science 292:1119 J. Miron, D. Ben-Ghedalia and M. Morrison. 2001. Invited review: Adhesion mechanisms of rumen cellulolytic bacteria. J. Dairy Sci. 84:1294
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James B. Russell and J.L. Rychlik. 2001. Factors that alter rumen microbial ecology.
J. Miron, D. Ben-Ghedalia and M. Morrison. 2001. Invited review: Adhesion
mechanisms of rumen cellulolytic bacteria. J. Dairy Sci. 84:1294
Bryan A. White. 1991. Bichemistry and genetics of microbial degradation of the
plant cell wall. Rec. Adv. on the Nutr. Herbivores. pp 217-225
J.L. Rychlik and J.B. Russell. 2002. Bacteriocin-like activity of Butyrivibrio fibrisolvens
JL5 and its effect on other ruminal bacteria and ammonia production. Appl. And Environ.
H. Krajcaraski-Hunt, J.C. Plaizier, J.-P. Walton, R. Spratt and B.W. McBride. 2002.
Short communication: Effect of subacute ruminal acidosis on in situ fiber digestion
in lactating dairy cows. J. Dairy Sci. 85:570
A.L. Oliver, R.J. Grant, J.F. Pedersen and J.O. O’Rear. 2004. Comparison of brown
midrib-6 and -18 forage sorghum with conventional sorghum and corn silage in diets of
lactating dairy cows. J. Dairy Sci. 87:637
Cell ContentCell Wall
Organic acids Pectins
Mammalian enzymes will digest starch and
sucrose (limited in ruminants)
Microbes digest the plant polysaccharides
Many plant cells have a primary cell wall, which accommodates the cell as it grows, and a secondary cell wall that develops inside the primary wall after the cell has stopped growing. The primary cell wall is thinner and more pliant than the secondary cell wall.
A specialized region of the cell walls of plants is the middle lamella. Rich in pectins, the middle lamella is shared by neighboring cells and cements them firmly together.
Secondary cell wall would develop
The main chemical components of the primary cell wall include cellulose and two groups of branched polysaccharides, the pectins and cross-linking glycans (hemicellulose). The secondary plant cell wall, which is often deposited inside the primary cell wall as a cell matures, contains lignin in addition to cellulose, but less hemicellulose and pectin.
3. Polysaccharides - polymers of sugar molecules
- Starch - polymer of glucose (plants)
- Glycogen - polymer of glucose (animals)
- Cellulose - polymer of glucose (plants)
Cellulose: A polymer of glucose units in β – 1,4 linkages. Cellulose is a linear molecule consisting of 1,000 to 10,000 β-D-glucose residues with no branching. Neighboring cellulose chains may form hydrogen bonds leading to the formation of microfibrils with partially crystalline parts. Hydrogen bonding among microfibrils can form microfibers and microfibers react to form cellulose fibers. Cellulose fibers usually consist of over 500,000 cellulose molecules.
Starch: A polymer of α-D-glucose in α-1, 4 linkages. Starch consists of two types of molecules, amylose and amylopectin. Amylose is a single chain of glucose units whereas in amylopectin at about every twenty glucose units there is a branch with an α-1, 6 linkage. The relative proportions of amylose to amylopectin depend on the source of the starch, e.g. normal corn contains over 50% amylose whereas 'waxy' corn has almost none (~3%). Amylose has lower molecular
weight with a relatively extended shape, whereas amylopectin has large but compact molecules.
Partial structure of amylose Partial structure of amylopectin
Amylose molecules consist of single mostly-unbranched chains with 500-20,000 α-(1, 4)-D-glucose units with a few α-1, 6 branches. Amylose can form an extended shape. Hydrogen bonding occurs between aligned chains. The aligned chains may form double stranded crystallites that are resistant to amylases.
Amylopectin is formed by non-random α-1, 6 branching of the amylose-type α-(1, 4)-D-glucose structure. This branching is determined by branching enzymes that leave each chain with up to 30 glucose residues. Each amylopectin molecule contains one to two million residues, about 5% of which form the branch points, in a compact structure forming granules. The molecules are oriented radially in the starch granule and as the radius increases so does the number of branches required to fill the space, resulting in concentric regions of alternating amorphous and crystalline structure.
- Pentosans - polymers of 5-carbon sugars
- Fructans – Water soluble chains of fructose
β-2-6 with β-2-1 branching
Found in temperate grasses
β-2-1 Found in Jerusalem artichokes
- β-Glucans – Soluble chains of glucose
β-1-3 and β-1-4 chains not linear like cellulose
Found in oats & barley
Pectins less in grass than legumes.
Hemicellulose greater in grass than legumes.
Hemicellulose and cellulose increase with maturity.
Non core lignin
Volatile components will be lost
Overheating causes reactions of carbohydrates with
proteins and changes solubility of carbohydrates
Starch & Sugars + Other
NFE = 100 - (moisture + ash + crude fiber + protein + ether extract)
Acid and sodium hydroxide used for crude fiber dissolve some cellulose, hemicellulose and lignin in cell walls which then are included in NFE.
(Neutral detergent solution)
Cell contents Cell walls (NDF)
Starch & Sugars Hemicellulose
(Pectin, β-glucans Cellulose
& fructans) Lignin
Soluble proteins Insoluble proteins
Lipids Insoluble minerals (dirt)
Fiber analysis - Detergent solutions (Van Soest)
NDF (Insoluble residue)
(Acid detergent solution)
Insoluble minerals (soil)
Acid detergent insol N (ADIN)
ADIN is unavailable protein - not digested in rumen
Klason Procedure (wood)
Feed (72% H2SO4) Lignin
Residue contains more than lignin
Protein, smaller molecular weight phenolics, cutin
Acid Detergent (proteins removed)
ADF (KMnO4) Lignin measured as
weight loss (Includes tannins
complexed with protein)
Cellulose, Cutin, minerals as residue
ADF (72% H2SO4) Cellulose measured as
Lignin, cutin, minerals as residue
NDF and ADF should be done sequentially on the same sample. Not done this way in most commercial labs. Pectin solubilized in ND soln, but not soluble in the AD soln.
Should report NDF and ADF on an organic basis. Minerals, especially soil, are not solubilized in the detergent solns.
Detergent system developed to measure fiber fractions in plant materials, not animal derived feeds.
Keratin proteins insoluble in ND soln. Add Na sulfite to dissolve
keratinized proteins but also attacks lignin.
Lipids interfere with NDF determination in feeds containing more than 10% lipids. ND is lipid soluble, so results in high NDF values.
Starch and cellulose both contain glucose.
1. Extract free sugars from the feed
2. Use enzymes specific for -linkage to digest
starch. (Amylase and Amyloglucosidase)
3. Measure glucose released
4. Starch = glucose x .9
Release of glucose following treatment of grain with amyloglucosidase provides an indication of availability starch in the rumen.
Open for inoculation from feed and water
Feed intake and feed retained in rumen and reticulum
Oxidation reduction potential –150 to –350 mv
Saliva NaHCO3, VFA, less from HPO4= at rumen pH
Eructation of gases and absorption of end products
Habitats in the Rumen
bacteria to plant material.
Protuberances from cells
probably are binding factors.
1. Transport of bacteria to fibrous substrate
Low numbers of free bacteria & poor mixing
2. Initial nonspecific adhesion
Electrostatic, hydrophobic, ionic
On cut or macerated surfaces
3. Specific adhesion to digestible tissue
Ligands or adhesins on bacterial cell surface
4.Proliferation of attached bacteria
Allows for colonization of available surfaces
Adherent cell Nonadherent cell
Glycocalyx (on outer membrane of cell)
Cellulose Cell Cell
Digested and fermented
Cellodextrins by adherent and
Gram+ cocci, usually in chains
Ferments cellulose, cellobiose & glucose
Produces acetic, formic, succinic, some lactic & H2
Ferments cellulose, cellobiose & glucose
Produces acetic, formic & succinic
Ferments cellulose, cellobiose, usually not sugars
Produces acetic, formic, lactic, ethanol & H2
Tolerate narrow pH range (pH 6 to 7)
Attach to feed particles
Added sugar was a source of readily available energy
from 0 to 24 h. Subsequent drop in pH after 24 h
limited the rate of cellulose digestion after 36 h.
Low pH (6.0)decreased rate
of cellulose digestion, but
had little effect on subsequent
ability to digest cellulose.
Similar results observed
ADP + Pi
Two methods to handle
Use energy to pump H+
out of the cell. Anion of
acid accumulates – toxic.
Let intracellular pH decline
to maintain a pH gradient.
Enzymes have to tolerate
low pH. S bovis produces
50% of microbial mass
proteins and fats.
Fungi can degrade cellulose, starch, xylan, hemicellulose & pectin
Some evidence of esterases that free CHOH from lignin
Ferments cellobiose, maltose, sucrose, glucose, fructose & xylose
Role of the fungi not clearly established in mixed cultures with
bacteria. Bacteria seem to inhibit the fungi.
Microbial cells 10%
Digestible unfermented feed 20%
Concentration of VFA in the rumen =
50 to 125 uM/ml
Protein in microbial mass 65%
Undegraded feed proteins 30%
Recycled endogenous proteins 5%
Amino acid balance of microbial mass is
superior to that from undegraded feed
proteins when corn-based diets are fed.