Carbohydrates in Animal Nutrition PDF

Carbohydrates in the nutrition of food- producing animals. Prof Dr Hamada Elshafii Carbohydrates are biochemical compounds composed only of the elements carbon, hydrogen and oxygen, and are the main source of energy for animals. Animals get the majority of their required energy from the carb...

Carbohydrates in the nutrition of food- producing animals. Prof Dr Hamada Elshafii Carbohydrates are biochemical compounds composed only of the elements carbon, hydrogen and oxygen, and are the main source of energy for animals. Animals get the majority of their required energy from the carbohydrates in feeds. Carbohydrates make up 75 % of the dry weight of the plant world, upon which animal life primarily depends.  The two major classes of carbohydrates in plants are known as non-structural and structural. Those that serve as storage and energy reserves and that are available for more rapid metabolism to supply energy (e.g., sugars, starch, and pectin) are referred to as non-structural carbohydrates (Nitrogen free extract).  Those CHO fractions that are not used for energy storage and provide fiber and anatomical features for rigidity and even water transport are known as structural carbohydrates (e.g., fibrous cellulose and hemi-cellulose). (crude fiber)  Non-structural CHO are more available for energy metabolism than the structural carbohydrates.  In this way, plants store the energy of the sun in products that can be used by animals as a source of energy for their life processes. Thus all animal life is dependent upon the process of photosynthesis.  The carbohydrates in plants are produced by means of photosynthesis. Radiant energy from the sun is captured by chlorophyll and changed to chemical energy, which in turn supports the formation of glucose from carbon dioxide and water. the overall process may be represented as follow:  6 CO2 + 6H2O + 673 Kcal ‑‑‑‑‑‑ C6H12O6 + 6O2 photosynthesis  Functions served by carbohydrates:  Carbohydrates are the major source of dietary metabolizable energy for poultry production.  Glycans are universally distributed and found in the cells and inter cellular space. These transmits biochemical signals into the cell and amongst the cells.  Blood glucose level should be maintained for normal body functions. The source may be glucogenesis from food or gluconeogenesis from fat and/or protein.  Participates in cell functions for protein and vitamins synthesis.  Indigestible fibrous carbohydrates are hygroscopic and facilitate defaecationThey help in peristaltic movement of food.  Carbohydrates are helpful in absorption of calcium and phosphorus in younger animals.  They provide suitable environment for the growth of rumen bacteria and protozoa.  They are also component of several important bio-chemical compounds such as nucleic acids, coenzymes and blood group substances.  Glycogen maltose  glycogen is stored glucose glucose is immediate energy glycogen is reserve energy  C. Oligosaccharide are made by bonding together three or more (3 to 15) monosaccharides bonded together.
Raffinose (glucose + fructose + galactose; 3 sugars) Stachyose (glucose + fructose + 2 galactose; 4 sugars) In animal diets, oligosaccharides are commonly found in beans and legumes. Some oligosaccharides are used as substances to enhance the growth of good microbes (prebiotics). Recently, there has been an increased interest in the use of different oligosaccharides as feed additives to enhance hindgut health (e.g., fructooligosaccharides, mannan oligosaccharides).  D. Polysaccharides, as their name implies, are made by joining together large polymers of simple sugars. Polysaccharides can be homopolysaccharides or heteropolysaccharides. a. Homopolysaccharide b. Heteropolysaccharide a. Homopolysaccharide: Contains only one type of saccharide unit. Examples of homopolysaccharides that are important in animal nutrition include starch (nonstructural form), glycogen (animal form ), and cellulose (plant structural form). Starch: Principal sugar form of carbohydrate in cereal grains (seed energy storage). The basic unit is α-D-Glucose. Forms of starch in cereal grains include ○ Amylose-α 1,4 linkage-straight chain, nonbranching, helical structure ○ Amylopectin-α 1,4 linkage with alpha 1,6 linkage at branch  Amylose is the simplest of the polysaccharides, being comprised solely of glucose units joined in an alpha 1,4 linkage (Figure 3.4). Amylose is water soluble and constitutes 15% to 30% of total starch in most plants. Amylopectin differs in how the glucose units are joined together. Alpha 1,4 linkages predominate, but a “branch” arises from an alpha 1,6 linkage. Such branches make the structure of amylopectin more complex than that of amylose. Amylopectin is not water soluble and constitutes 70% to 85% of total starch in plant cells. Starch is the chief carbohydrate source in the diet of monogastric animals. Amylopectin is the major form of starch in plant cells. Starch Major storage carbohydrate in higher plants Amylose – long straight glucose chains (α1-4) Amylopectin – branched every 24-30 glc residues (α 1 -6) Provides 80% of dietary calories in humans worldwide  Glycogen Major storage carbohydrate in G animals G G G G G Long straight glucose chains (α 1-4) G G G G G Branched every 4-8 glc residues (α G GG  1-6 link 1-6) GG  1-4 link G More branched than starch G Less osmotic pressure G Easily mobilized Carbohydrate 15  non-starch polysaccharides. NSP are mainly present in the cell walls of the endosperm but also in the bran. They include cellulose, hemi- cellulose (arabinoxylans and beta-glucans) and pectin, and can also be divided according to their nutritional value into water-soluble (beta -glucans and pectins) and water-insoluble (cellulose) fractions. Cereals contain between 7 and 19% of NSP.
 The main difference between NSPs and starch is that, starch is composed entirely of glucose monomers, which are linked by α-glycosidic bonds while NSPs are composed of different kinds of monomers, which are linked predominantly by β-glycosidic bond. The difference in bonding structure has profound effects on digestibility, as different classes of enzymes are required for the hydrolysis of α- and β-glycosidic bond. The predominant starch digestive enzymes are α-amylase, α-glucosidase and oligo-1-6-glucosidase. In combination, these enzymes specifically hydrolyse the α-glycoside bonds of starch to yield glucose. 17  NSPs can be broadly classified into:
Insoluble fibers include cellulose, hemicellulose and pentosans like xylans and arabinoxylans, and Soluble fibers include mixed linked b-glucans, galactomannan (guar-gum) and pectins. Higher concentration of soluble non starch polysaccharides is not desirable in the diets of poultry due to following reasons: 1. Soluble non starch polysaccharides like pentosans increase viscosity of digesta resulting in higher rate of passage and lowering of digestion of nutrients and duration of absorption of nutrients. 2. These are indigestible in poultry and occupy the space of digestible constituents of the feedstuffs. 3. The performances of birds decrease due to reduced availability of nutrients These are, therefore, considered anti nutritional factors. 18 Fiber in animal nutrition
Crude Fiber (CF): Crude fiber is a traditional measure of fiber content in feeds. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) are more useful measures of feeding value, and should be used to evaluate forages and formulate rations. Neutral Detergent Fiber (NDF): Structural components of the plant, specifically cell wall. NDF is a predictor of voluntary intake because it provides bulk or fill. In general, low NDF values are desired because NDF increases as forages mature. Acid Detergent Fiber (ADF): The least digestible plant components, including cellulose and lignin. ADF values are inversely related to digestibility, so forages with low ADF concentrations are ususally higher in energy. Digestion, absorption, and metabolism of carbohydrates by non‑ ruminants:
There are three basic actions of the body which effect these changes: 1‑ Digestion or the preparation of food for entrance into the blood stream. 2‑ Absorption into the blood stream of the molecules derived from digestion, 3‑ Metabolism of the absorbed nutrients for use by the body and/or subsequent excretion.  Non-Ruminant Carbohydrate Digestion Mouth  Salivary amylase  Breaks starches down to maltose  Plays only a small role in breakdown because of the short time food is in the mouth  Ruminants do not have this enzyme  Not all monogastrics secrete it in saliva  Digestion Pre-stomach – Salivary amylase :  1-4 endoglycosidase G G G G G G G  Limit dextrins GGG GG G GG GG G amylase G G G  1-6 link GGG GG maltotriose  1-4 link GG GG GG maltose G G isomaltose  Carbohydrate Digestion Pancreas  Pancreatic amylase  Hydrolyzes alpha 1-4 linkages  Produces monosaccharides, disaccharides, and polysaccharides  Major importance in hydrolyzing starch and glycogen to maltose Polysaccharides Amylase Disaccharides Small Intestine Pancreatic enzymes -amylase maltotriose maltose G G G G G G G G + G G amylose  amylase G G G G G G G G GG GG G G GG G amylopectin  Limit dextrins Digestion in Small Intestine Sucrase Sucrose Glucose + Fructose * Ruminants do not have sucrase Maltase Maltose Glucose + Glucose Lactase Lactose Glucose + Galactose * Poultry do not have lactase  Overview Monogastric Carbohydrate Digestion Location Enzymes Form of Dietary CHO Mouth Salivary Amylase Starch Maltose Sucrose Lactose Stomach (amylase from saliva) → Dextrin Maltose Small Intestine Pancreatic Amylase Maltose Brush Border Enzymes Glucose Fructose Galactose + + + Glucose Glucose Glucose Large Intestine None Bacterial Microflora Ferment Cellulose Digestion in Large Intestine Carnivores and omnivores  very low anaerobic fermentation  Bacteria produce small quantities of cellulase  Volatile fatty acid (VFA) produced by microbial digestion of fibers  Propionate  Butyrate  Acetate  Digestion in Large Intestine Caudal fermentors, aka cecal digestors - e.g., Horses & rabbits Have Limited anaerobic fermentation, Bacteria (in cecum and colon) produce small quantities of cellulase (Can utilize large quantities of cellulose), Volatile fatty acid (VFA) produced by microbial digestion of fibers.  Can utilize large quantities of cellulose  Cecum and colon contain bacteria which produce cellulase Carbohydrate absorption Hexose transporter apical basolateral  Monogastric animals do not secrete enzymes that digest the complex carbohydrates (β 1,4 linkages; e.g., nonstarch polysaccharides [NSP], glucans, cellulose) that are components of plant fiber (e.g., wheat, barley) and are acted upon by hindgut microbes to yield volatile fatty acids (VFAs). High levels of NSP and glucans in a monogastric diet can cause viscous digesta and can interfere with digestion processes leading to malabsorption. In poultry, high-NSP-containing diets (e.g., barley, rye) can produce wet litter, dirty eggs, and diarrhea. The absorption of glucose, galactose, and fructose is an active process utilizing a specific carrier protein that translocates the molecules across the brush border membrane. Fructose is transported less rapidly than the others suggesting a somewhat different mechanism. Energy is required and Na and K ions are involved. + + - Absorbed carbohydrate in the form of glucose, galactose and fructose are metabolized The fate of glucose; 1‑ As an immediate source of energy. 2‑ As a precursor of liver and muscle glycogen, and, 3‑ As a precursor of tissue triglyceride  How Cells Derive Energy from Glucose: Metabolic Pathways Two major pathways of glucose catabolism are glycolysis and the TCA cycle One mole of glucose, if burned in a flame, liberates 674 kcal of heat. oxidation of glucose in an animal’s body allows for the recovery of the chemical bond energy of glucose in a useable form. Energy is needed for life processes including heart work, protein synthesis, fat synthesis, milk synthesis, or meat and egg production. Different metabolic pathways such as glycolysis, tricarboxylic acid (TCA), and the electron transport system, plus one enzyme, pyruvate dehydrogenase (PDH), allow efficient conversion of glucose chemical bond energy into useable energetic intermediates such as ATP. Glycolysis yield two net ATP / glucose molecule plus two NADH. Because NADH can be metabolized to ATP and because we get two NADH from each glucose molecule, the net ATP yield per glucose in glycolysis is eight. Glycolysis: Net Gain of ATP
Input = 2 ATP Produces = 4 ATP and 2 NADH Net gain = 8 ATP (aerobic) Small Intestine Carbohydrates Monosaccharides Portal Vein Active Transport Distributed to Liver tissue through circulation Digestion, absorption and metabolism of carbohydrates by ruminants

Carbohydrate digestion in ruminant animals is through microbial fermentation in the rumen. Dietary carbohydrates are degraded (fermented) by rumen microbes (bacteria, fungi, protozoa). The purpose of rumen fermentation is to produce energy as ATP for the bacteria to use for protein synthesis and their own growth The foods of ruminants, forages and fibrous roughages, consist mainly of β-linked polysaccharides such as cellulose, which cannot be broken down by mammalian digestive enzymes. Ruminants have therefore evolved a special system of digestion that involves microbial fermentation of food before its exposure to their own digestive enzymes.  The end products of rumen fermentation are microbial cell masses, or microbial protein-synthesized VFA, and gases such as carbon dioxide, methane, hydrogen, and hydrogen sulfide. The products of fermentation will vary with the relative composition of the rumen microflora. The microbial population also depends on the diet, since this changes the substrates for fermentation and subsequently the products of fermentation. For example, starch is the major dietary constituent in concentrate-fed ruminants (e.g., feedlot cattle). The rumen of such animals will have higher amylolytic bacteria than cellulolytic bacteria present in the rumen of roughage- and pasture-fed animals.  Factors such as the forage:concentrate ratio, the physical form of the diet (ground vs. pelleted), feed additives, and animal species can affect the rumen fermentation process and VFA production.
Molar ratios of VFAs are dependent on the forage:concentrate ratio of the diet. Cellulolytic bacteria tend to produce more acetate, while amylolytic bacteria produce more propionic acid. Typically three major VFA molar ratios are 65:25:10 with a roughage diet and 50:40:10 with a concentrate-rich diet. Changes in VFA concentration can lead to several disorders of carbohydrate digestion in ruminants. Rumen acidosis occurs when animals are fed high-grain-rich diets or when animals are suddenly changed from pasture- or range-fed to feedlot conditions. 40  Grouping of rumen bacterial species according to the type of substrates fermented. Carbohydrate Digestion
in Ruminants Ingested carbohydrates are exposed to extensive pregastric fermentation  Most carbohydrates fermented by microbes before they can be exposed to typical gastric and small intestinal enzymes Rumen fermentation is highly efficient considering the feedstuffs ingested Bacterial Digestion of Carbohydrates Rumen: Microbes attach 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 particles prior to digesting them  The simple sugars produced in the first stage of carbohydrate digestion in the rumen are rarely detectable in the rumen liquor because they are immediately taken up and metabolised intra‑ cellular by the micro‑organisms. The main end products of the metabolism of carbohydrates by rumen micro‑organisms are acetic, propionic and butyric acids, and carbon dioxide and methane. Rumen Fermentation Gases (carbon dioxide and methane) are primary byproducts of rumen fermentation Usually these gases are eructated or belched out - if not, bloat occurs Bloat results in a severe distension of the rumen typically on the left side of the ruminant and can result in death  Ruminant Carbohydrate Digestion  Small Intestine  Secretion of digestive enzymes  Digestive secretions from pancreas and liver  Further digestion of carbohydrates  Absorption of H2O, minerals, amino acids, glucose, fatty acids Cecum and Large Intestine Bacterial population ferments the unabsorbed products of digestion  Absorption of H2O, VFA and formation of feces The animal uses the volatile fatty acids as follows: ‑ Acetic and butyric acids are used as sources of energy. ‑ Acetic and butyric acids also serve in synthesis of milk fat. - Propionic acid is converted to glucose (glucogenic). The typical composition of rumen gas is: Co2 40% Methane 30‑40% Hydrogen 5% Oxygen trace amount Nitrogen trace amount Most of the gas produced is lost by eructation; if gas accumulates it causes the condition known as bloat.  Volatile Fatty Acids Carbohydrates VFA’s Microbial Fermentation Glucose  Short-chain fatty acids produced by - Rumen, cecum, colon microbes O O O CH C CH CH C CH CH CH C  3 basic types: 3 3 2 3 2 2 O O O Acetic acid (2c) Propionic acid (3c) Butyric acid (4c)  VFA Formation 2 acetate + CO2 + CH4 + heat 1 Glucose 2 propionate + water 1 butyrate + CO2 + CH4 VFAs absorbed passively from rumen to portal blood Provide 70-80% of ruminant’s energy needs The three major VFAs (acetic, propionic, butyric) absorbed from the rumen have somewhat distinctive metabolic fates: 1- Acetic acid is utilized minimally in the liver and is oxidized throughout most of the body to generate ATP. Another important use of acetate is as the major source of acetyl CoA, and it enters the TCA cycle. Acetic acid is used for the synthesis of lipids (e.g., milk or body fat). 2- Propionic acid is almost completely removed from portal blood by the liver. Propionate is converted to succinyl CoA, and it enters the TCA cycle. Within the liver, propionate serves as a major substrate for gluconeogenesis, in a dairy cow, all the glucose in the milk lactose was synthesized in the liver and most of that synthesis was from propionic acid. Absorption of VFAs all simple passive diffusion VFA metabolism in the rumen wall ○ Cells use most of the butyrate for their own energy needs ○ Acetate and propionate are ‘exported’ to blood VFA Production – Molar Ratios Forage:Grain Acetate Propionate Butyrate 100:0 71.4 16.0 7.9 75:25 68.2 18.1 8.0 50:50 65.3 18.4 10.4 40:60 59.8 25.9 10.2 20:80 53.6 30.6 10.7 Rumen VFA Profiles Microbial Populations Cellulolytic bacteria (fiber digesters) →  Produce cellulase - cleaves β1 4 linkages  Primary substrates are cellulose and hemicellulose  Prefer pH 6-7  Produce acetate, propionate, little butyrate, CO2  Predominate in animals fed roughage diets Microbial Populations Amylolytic bacteria (starch, sugar digesters)  Digest starches and sugars  Prefer pH 5-6  Produce propionate, butyrate and sometimes lactate  Predominate in animals fed grain diets  Rapid change to grain diet causes lactic acidosis (rapidly decreases pH) Streptococcus bovis  Microbial Metabolism Sugars ADP Biosynthesis Catabolism ATP in rumen: VFA NADP+ CO2 Growth CH4 NADPH Maintenance Heat Replication