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TRIOSES GLYCERALDEHIDE DIHYDROXYACETONE
MONOSACHARIDES TETROSES ERYTHROSE
PENTOSES ARABINOSE XYLOSE XYLULOSE RIBOSE RIBULOSE
HEXOSES GLUCOSE
SUGARS GALACTOSE MANNOSE FRUCTOSE
HEPTOSES SEDOHEPTULOSE
DISACHARIDES SUCROSE, LACT,MAL,CELLOB OLIGOSACHARIDES TRISACHARIDES RAFFINOSE, KESTOSE
TETRASACHARIDES STACHYOSE
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ARABINANS XYLANS HOMOGLYCANS GLUCANS STARCH DEXTRINS GLYCOGEN CELLULOSE CALLOSE
FRUCTANS INULIN LEVAN GALACTANS POLYSACHARIDES MANNAN GLUCOSAMINES PECTIC SUBS. HETEROGLYCANS HEMICELLULOSE
NON SUGARS EXUDATE ACIDIC HYALURONIC CHONDROITIN COMPLEX GLYCOLIPIDS CARBOHYDRATE GLYCOPROTEIN
Properties of the monosaccharides Pentoses (L-Arabinose) Hexoses
D-Glucose (grape sugar or dextrose) D-Fructose (fruit sugar or laevulose) D-Mannose D-Galactose
Heptoses (D-Sedoheptulose)
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Lignin, which is not a carbohydrate but is closely associated with this group of compounds, confers chemical and biological resistance to the cell wall, and mechanical strength to the plant. Strictly speaking the term 'lignin
is of par;cular interest in animal nutri;on because of its high resistance to chemical degrada4on.
DigesCon and AbsorpCon Non-ruminant Ruminant
CHO in feed digestive enzymes
Glucose in small intestine
Absorption into blood circulation
microbial fermentation
Volatile fatty acids in rumen
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Monosaccharides Do not need hydrolysis before absorp;on Very li>le (if any) in most feeds
Di- and poly-saccharides Rela;vely large molecules Must be hydrolyzed prior to absorp;on Hydrolyzed to monosaccharides
Only monosaccharides can be absorbed
Mouth Salivary amylase
Breaks starches down to maltose Plays only a small role in breakdown because of the short ;me food is in the mouth Ruminants do not have this enzyme Not all monogastrics secrete it in saliva
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Pancreas PancreaCc amylase
Hydrolyzes alpha 1-4 linkages Produces monosaccharides, disaccharides, and polysaccharides Major importance in hydrolyzing starch and glycogen to maltose
Polysaccharides Disaccharides Amylase
Diges;on mediated by enzymes synthesized by cells lining the small intes;ne (brush border)
Disaccharides Monosaccharides Brush Border Enzymes
* Excep;on is -1,4 bonds in cellulose
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Maltose Glucose + Glucose Maltase
Lactose Lactase Glucose + Galactose
* Poultry do not have lactase
Sucrose Glucose + Fructose Sucrase
* Ruminants do not have sucrase
Newborns have a full complement of brush-border enzymes
Miller et al. (eds.), 1991
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Carnivores and Omnivores Limited anaerobic fermenta;on Bacteria produce small quan;;es of cellulase Vola;le fa>y acid (VFA) produced by microbial diges;on of fibers
Propionate Butyrate Acetate
Post-gastric fermenters (horse and rabbit)
Can u;lize large quan;;es of cellulose Cecum and colon contain bacteria which produce cellulase Cellulase is capable of hydrolyzing the glucose-4-beta-glucoside linkage
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Location Enzymes Form of Dietary CHO Mouth Salivary Amylase Starch Maltose Sucrose Lactose Stomach (amylase from saliva) DextrinMaltose Small Intestine Pancreatic Amylase Maltose Brush Border Enzymes Glucose Fructose Galactose + + + Glucose Glucose Glucose Large Intestine None Bacterial Microflora Ferment Cellulose
With excep;on of newborn animal (first 24 hours), no di-, tri-, or polysaccharides are absorbed
Monosaccharides absorbed primarily in duodenum and jejunum
Li>le absorp;on in stomach and large intes;ne
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Carbohydrates Monosaccharides
AcCve Transport
Liver
Portal Vein
Distributed to ;ssue through circula;on
Ac4ve transport for glucose and galactose Sodium-glucose transporter 1 (SGLT1) Dependent on Na/K ATPase pump
Facilitated transport for fructose
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Consist of starches, glycogen, sucrose, lactose, glucose, fructose Polysaccharides broken down to monosaccharides Monosaccharides taken up by ac;ve transport or facilitated diffusion
and carried to liver Glucose is transported to cells requiring energy
Insulin influences rate of transport
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Ingested feed is exposed to extensive pregastric fermenta4on
Rumen fermenta4on is highly efficient considering the feedstuffs ingested
Most ingesta fermented by microbes before it is exposed to typical gastric and small intes;nal enzymes
Favorable environment for survival and ac4vity of anaerobic microbes
Almost all carbohydrate is fermented in the rumen
25 to 50 million bacteria/ml Warm, moist environment Ferment cellulose, starch, and soluble carbohydrate
Some bypass starch may escape to the small intes;ne Do not have salivary amylase, but have plenty of pancrea;c amylase to digest starch
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Celluloly4c bacteria (fiber digesters) Produce cellulase - cleaves 1 4 linkages Prefer pH 6-7 U;lize N in form of NH3 Require S for synthesis of sulfur-containing amino acids (cysteine and methionine) Produce acetate, propionate, li>le butyrate, CO2 Predominate in animals fed roughage diets
Amyloly4c bacteria (starch, sugar digesters) Digest starch Prefer pH 5-6 U;lize N as NH3 or pep;des Produce propionate, butyrate and lactate Predominate in animals fed grain diets Rapid change to grain diet causes lac;c acidosis (rapidly decreases pH) Streptococcus bovis
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ADP ATP NADP+ NADPH
Sugars
Catabolism
Biosynthesis
Growth Maintenance Replication
VFA CO2 CH4 Heat
in rumen:
Microbes aKach to (colonize) fiber components and secrete enzymes Cellulose, hemicellulose digested by cellulases and hemicellulases
Complex polysaccharides are digested to yield sugars that are fermented to produce VFA
Starches and simple sugars are more rapidly fermented to VFA
Protozoa engulf starch par4cles prior to diges4ng them
Rumen:
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Small Intes4ne
Cecum and Large Intes4ne
Secre;on of diges;ve enzymes Diges;ve secre;ons from pancreas and liver Further diges;on of carbohydrates Absorp;on of H2O, minerals, amino acids, glucose, fa>y acids
Bacterial popula;on ferments the unabsorbed products of diges;on Absorp;on of H2O, VFA and forma;on of feces
Composi4on and Diges4on of Carbohydrate Frac4ons
___________________________________________________________ Composi4on Rumen Diges4on (%/h) _____________________________________________________ Sugars 200-350 FermentaCon and Organic Acids 1-2 Starch 10-40 Soluble Available Fiber 40-60 PecCns B glucans Insoluble Available Fiber 2-10 Cellulose Hemicellulose Unavailable Fiber (lignin) 0
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a
Carbohydrates VFAs
Glucose
Microbial Fermenta;on
Short-chain fa>y acids produced by microbes
3 basic types:
- Rumen, cecum, colon
AceCc acid (2c)
CH3 CO
OCH2 C
O
OCH3 CH2 C
O
OCH2CH3
Propionic acid (3c) Butyric acid (4c)
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2 acetate + CO2 + CH4 + heat
2 propionate + water
1 butyrate + CO2 + CH4
1 Glucose
VFAs absorbed passively from rumen to portal blood Provide 70-80% of ruminants energy needs
Gases (carbon dioxide and methane) are primary byproducts of rumen fermenta;on
Usually these gases are eructated or belched out - if not, bloat occurs
Bloat results in a severe distension of the rumen on the lek side of the ruminant and can result in death
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Acetate Energy Fa>y acid synthesis
Propionate Energy Gluconeogenic glucose synthesis
Butyrate Energy Rumen epithelial cells
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