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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