Carbohydrates in Animal Sciences 223

Carbohydrates in Animal Sciences 223

Learning Objectives

  • List various carbohydrates (CHO) and their chemical properties

  • Describe why and where CHO exist in plants

  • Understand why some CHO are not tolerated by animals at different life-stages

  • Describe how CHO are digested and absorbed

  • Classify polysaccharides based on how they are used by animals

  • Explain the process of dietary fiber fermentation

  • Consider how energy is derived from CHO

Plant Carbohydrates and Cell Contents

Structure of Plant Carbohydrates

  • Components:
      - Cell Wall
        - Primary wall
        - Secondary wall
        - Middle lamella
        - Plasma membrane
      - Cell Contents:
        - Endosperm
        - Germ
        - Tip Cap

Types of Carbohydrates in Plants

  • Carbohydrates include:
      - Starch
      - Disaccharides
      - Oligosaccharides
        - Including fructooligosaccharides
      - Fructan polysaccharides
      - β-Glucans
      - Pectins and Gums
      - Hemicelluloses
      - Cellulose
      - Lignin/Phenolics

  • Total dietary fiber breakdown:
      - CHO-H (Hydrolytically digestible carbohydrates)
      - CHO-FR (Rapidly fermentable carbohydrates)
      - CHO-FS (Slowly fermentable carbohydrates)

Energy from Carbohydrates vs. Fat

  • Energy Density Comparison:
      - CHO: 4 kcal/g
      - Fat: 9 kcal/g

  • Dietary Inclusion (% of diet):
      - CHO: 70%
      - Fat: 7%

  • Amount in 1000 g of diet:
      - CHO: 700 g
      - Fat: 70 g

  • Total energy provided by nutrient:
      - CHO: 2800 kcal
      - Fat: 630 kcal

  • Proportion of total energy:
      - CHO: 82%
      - Fat: 18%

Overview of Carbohydrates

  • Carbohydrates constitute a significant portion of diets for various animal types:
      - Companion animals (pet food)
      - Monogastric animals (swine, poultry)
      - Hindgut fermenters (horse)
      - Ruminants (sheep and cattle)

  • General Notes:
      - No absolute dietary requirement for carbohydrates; glucose can be synthesized from amino acids (protein) via gluconeogenesis.
      - Carbohydrates are major energy sources for plants and represent 60% to 90% of dry matter weight.

Classification of Carbohydrates

  • Categories:
      - Monosaccharides (simple sugars)
      - Disaccharides (2 units)
      - Oligosaccharides (3-10 units)
      - Polysaccharides (>10 units)

Important Monosaccharides

  1. Glucose
       - Chemical formula: C₆H₁₂O₆
       - Major product of carbohydrate digestion in monogastric animals.

  2. Galactose
       - Part of lactose; less sweet and less soluble than glucose.

  3. Fructose
       - The sweetest sugar; part of sucrose.

Additional Monosaccharides

  • Mannose: Benefits from non-nutritive effects.

  • Ribose: Part of nucleic acids.

  • Xylose and Arabinose: Aldopentoses, contribute to arabinoxylan.

Digestion and Absorption of CHO

Digestion Process

  • Monosaccharides are absorbed directly.

  • Disaccharides must be hydrolytically digested before absorption, which primarily occurs in the small intestine.

  • Undigested carbohydrates will be fermented by colonic bacteria.

Gastrointestinal Structure

  • Structure includes:
      1. Stomach
      2. Small Intestine
         - Duodenum
         - Jejunum
         - Ileum
      3. Large Intestine (Colon and Cecum)

  • Fermentation primarily occurs in the large intestine.

Small Intestinal Structure

  • Contains folds (Kerckring), villi, and microvilli that increase surface area for absorption.
      - Villi and microvilli enhance nutrient absorption significantly.

Types of Disaccharides

  • Composed of two monosaccharide units:
      1. Maltose: Glucose + Glucose (alpha(1→4) linkage)
         - Found in malt and used in beer brewing.
      2. Sucrose: Glucose + Fructose (C1 linked to C2)
         - Commonly found as table sugar (produced from sugar cane, beets).
      3. Lactose: Glucose + Galactose (beta(1→4) linkage).
         - Known as milk sugar; key energy source for suckling animals.

Importance of Lactose

  • Nutrient Content of Milk:
      - Varies significantly across species:
        - Elephant: 22.1% fat, 3.2% protein, 7.4% lactose
        - Human: 4.0% fat, 1.3% protein, 6.5% lactose
        - Cow: 3.7% fat, 3.3% protein, 4.8% lactose

  • Lactose Digestion:
       - Activity decreases with age in adult animals. Sometimes leading to diarrhea when fed milk.
       - Small quantities of dairy products can still be digested by adults.
       

Oligosaccharides in Diet

Types of Oligosaccharides

  • Alpha-galactosides: Includes raffinose, stachyose, verbascose.
      - Found in legumes; cause flatulence when consumed in significant amounts.

  • Fructooligosaccharides (FOS): Not digested by mammals; may be used as a non-nutritive sweetener.

Prebiotics and Probiotics

  • FOS promotes beneficial bacterial growth in the gut, enhancing gut health and often suppressing pathogenic bacteria.

  • Prebiotic: Non-digestible ingredient stimulating specific bacteria growth in the digestive system for health benefits.

  • Probiotic: Live microorganisms that confer health benefits when consumed in adequate amounts.

Polysaccharides Overview

Structure and Importance

  • Composed of more than 10 monosaccharide units, often containing hundreds or thousands of units.

  1. Starch: Major carbohydrate source in animal feeds; found in seeds (70%) and tubers (30%).

  2. Glycogen: Storage polysaccharide in liver/muscle, highly branched structure.

  3. Cellulose: Provides plant structure; indigestible by mammalian enzymes.

Starch and Gelatinization Process

  • Starch: Composed of amylose and amylopectin.

  • Gelatinization: Occurs when starch granules swell and bind water, forming a gel.
      - Cooking causes irreversible changes making starch soluble.

Dietary Fiber

  • Comprised of non-digestible plant carbohydrates, including:
      - Lignin: Provides rigidity, found in mature plants.
      - Cellulose: A beta(1→4) linked glucose polymer; slow to ferment.
      - Hemicelluloses: More fermentable than cellulose, composed of various sugars.
      - Pectin: Rapidly fermented, often used for health benefits.

Fermentation in Gut

  • Microbial breakdown of dietary fiber leading to short-chain fatty acids (SCFA) and gases.

  • Key SCFAs include: Acetate, propionate, and butyrate, especially important for ruminants.

Importance of Fiber in Diet

  • Promotes gastrointestinal health, normalizes stool, and influences nutrient absorption.

  • Benefits of Dietary Fiber:
      - Increases hydration of the colon and prevents constipation.
      - Improves gut health and reduces transit time through the intestines.

Fiber Sources in Pet Foods

  • Common indigestible fiber sources include:
      - Beet pulp, apple pomace, peanut hulls, bran of various grains.

  • Commercial pet food labels generally indicate crude fiber content (3-6%).

Evaluation of Pet Food and Nutrient Digestibility

  • Commercial pet foods vary significantly in digestibility and nutrient availability.

  • Importance of carbohydrate source, processing, and dietary fiber on overall nutrition.

Conclusion: Bringing it All Together

  • Carbohydrate fractions are crucial for the understanding and formulation of animal diets.

  • Variability in digestibility relates to ingredient sourcing and processing methods for optimal nutrition in both pets and livestock.

Learning Objectives

  • List various carbohydrates (CHO) and their chemical properties: Understanding the fundamental structures and classifications of carbohydrates, including their monomeric and polymeric forms.

  • Describe why and where CHO exist in plants: Carbohydrates primarily serve as energy storage and structural components in plants, found in organs such as leaves, stems, and roots.

  • Understand why some CHO are not tolerated by animals at different life-stages: Certain carbohydrates may induce gastrointestinal distress due to factors like enzyme deficiency or changes in gut microbiota composition as animals age.

  • Describe how CHO are digested and absorbed: Outlining the enzymatic breakdown of carbohydrates in the gastrointestinal tract, emphasizing the role of enzymes such as amylase.

  • Classify polysaccharides based on how they are used by animals: Differentiating between storage polysaccharides (like starch and glycogen) and structural polysaccharides (like cellulose and hemicellulose).

  • Explain the process of dietary fiber fermentation: Detailing the microbial fermentation process in the large intestine and the byproducts of fermentation, such as short-chain fatty acids (SCFAs) that play a crucial role in gut health and energy metabolism.

  • Consider how energy is derived from CHO: Discussing the metabolic pathways through which carbohydrates are converted into glucose and subsequently utilized for energy, including glycolysis and the citric acid cycle.

Plant Carbohydrates and Cell Contents
Structure of Plant Carbohydrates

  • Components:
      - Cell Wall: Provides structural support and protection, made up of cellulose, hemicellulose, and lignin.
      - Primary wall: Composed mainly of cellulose and pectin, providing flexibility.
      - Secondary wall: Thicker layer, more lignified, conferring additional strength.
      - Middle lamella: A pectin layer that cements adjacent cells together.
      - Plasma membrane: Semi-permeable barrier that regulates cell transport.
      - Cell Contents:
        - Endosperm: Nutrient storage tissue in seeds, rich in carbohydrates, particularly starch.
        - Germ: Embryo of the seed, which develops into a new plant.
        - Tip Cap: Protective covering at the tip of the seed that aids in breaking dormancy.

Types of Carbohydrates in Plants

  • Carbohydrates include:
      - Starch: Storage form of carbohydrates in plants, consisting of amylose and amylopectin.
      - Disaccharides: Two monosaccharide units; important examples include sucrose, lactose, and maltose.
      - Oligosaccharides: Chains of 3-10 monosaccharides, such as raffinose and stachyose.
      - Fructooligosaccharides: Prebiotic compounds important for gut health.
      - Fructan polysaccharides: Reserve carbohydrates in some plants, helping in stress tolerance.
      - β-Glucans: Found in cereals, known for their health benefits, including cholesterol reduction.
      - Pectins and Gums: Contribute to cell wall structure and water retention.
      - Hemicelluloses: Matrix polysaccharides that support cellulose in cell walls.
      - Cellulose: Provides rigidity and is a major component of the plant cell wall.
      - Lignin/Phenolics: Non-carbohydrate components that add strength and protection to plant tissues.

  • Total dietary fiber breakdown:
      - CHO-H (Hydrolytically digestible carbohydrates): Easily broken down by digestive enzymes.
      - CHO-FR (Rapidly fermentable carbohydrates): Fermented quickly by gut bacteria.
      - CHO-FS (Slowly fermentable carbohydrates): Fermented at a slower rate, providing a sustained energy source.

Energy from Carbohydrates vs. Fat

  • Energy Density Comparison:
      - CHO: 4 kcal/g, providing a quicker source of energy for immediate use.
      - Fat: 9 kcal/g, serves as a long-term energy reserve.

  • Dietary Inclusion (% of diet):
      - CHO: 70% in many animal diets, particularly in herbivores.
      - Fat: 7%, often limited to avoid excess caloric intake.

  • Amount in 1000 g of diet:
      - CHO: 700 g typically included in standard pet and livestock feeds.
      - Fat: 70 g, providing supplementary energy.

  • Total energy provided by nutrient:
      - CHO: 2800 kcal derived, essential for high-energy activities.
      - Fat: 630 kcal, providing sustained energy during prolonged physical activities.

  • Proportion of total energy:
      - CHO: 82%, reflecting its significance in maintaining energy levels.
      - Fat: 18%, highlighting its role as a secondary energy source.

Overview of Carbohydrates

  • Carbohydrates constitute a significant portion of diets for various animal types:
      - Companion animals (pet food): High levels of carbohydrates to ensure palatability and energy.
      - Monogastric animals (swine, poultry): Require readily digestible carbohydrates for optimal growth.
      - Hindgut fermenters (horse): Dependent on fibrous carbohydrates for digestive health and energy.
      - Ruminants (sheep and cattle): Utilize complex carbohydrates for microbial fermentation, crucial for digestion.

  • General Notes:
      - No absolute dietary requirement for carbohydrates; glucose can be synthesized from amino acids (protein) via gluconeogenesis, showcasing metabolic flexibility.
      - Carbohydrates are major energy sources for plants and represent 60% to 90% of dry matter weight, illustrating their foundational role in plant biology.