Non-ruminant Digestion

Non-ruminant Digestion AS 223 Study Notes

Learning Objectives

  • 1. Understand the main functions of the non-ruminant and avian gastrointestinal tract (GIT)

  • 2. Understand and describe the major digestive enzymes

  • 3. Understand the role of the liver and pancreas in digestion

  • 4. Understand the role of forage/roughage in hindgut fermenters

Comparative Digestive Anatomy

  • Quote: "The body is nothing more than a hollow dirty tube."

  • Adaptation: The GIT is an adaptation to the animal’s food environment.

What is Digestion?

  • Definition: The process of mechanical, chemical, and enzymatic breakdown of food/feed into substances for absorption into the bloodstream.

Main Types of Non-ruminant G.I. Tracts

  1. “Simple” stomach (e.g., pigs)

  2. Hindgut fermenter (e.g., horses)

  3. Avian (e.g., chickens)

  • Additional examples include rhinoceros, elephant, guinea pig, rat, human, rodent, dog, and cat.

Comparative Anatomy of G.I. Tracts

  • Example: Pony

    • Pony (Equus caballus)

    • Body Length: 164 cm

  • Example: Dog

    • Begante family

    • Body Length: 90 cm

  • Example: Sheep

    • Body Length: 110 cm

Basic Anatomy of the Simple Stomach G.I.T.

  • Components Include:

    • Mouth

    • Esophagus

    • Stomach

    • Duodenum

    • Large intestine

    • Ileum

    • Jejunum

    • Cecum

    • Anus

Relationships of Different Body Systems

  • Digestive System:

    • Food, water intake

    • Nutrients, water, salt

  • Respiratory System:

    • Oxygen intake

    • Elimination of CO₂

  • Circulatory System:

    • Transport to and from cells

  • Urinary System:

    • Elimination of excess water, salts, and wastes

Three Forces Acting on Food in the G.I.T. to Facilitate Digestion

  1. Mechanical: Chewing

  2. Chemical: Hydrochloric acid (HCl)

  3. Enzymatic: Pepsin

Mouth Functions

  1. Prehension: Bring food into mouth

  2. Mastication: Chewing food

  3. Insalivation: Mixing saliva with food (first stage of chemical digestion)

    • Salivary Amylase: Initiates carbohydrate digestion

    • Lingual Lipase: Initiates lipid digestion

Importance of Lingual Lipase in Neonates

  • Function: Enzyme secreted by glands on the tongue present at birth; helps with fat digestion in neonates and nutrient absorption.

Esophagus

  • Description: A tube that connects the mouth to the stomach.

  • Peristalsis: Involuntary muscle contractions and relaxations that move food to the stomach.

Stomach

  • Structure: Contains many sac-like structures that help store food.

  • Regions of the Stomach:

    • Cardiac

    • Fundic

    • Pyloric

  • Components: Mucus, HCl, Zymogens, Gastrin (stimulates contractions and aids in gastric motility).

Role of Zymogens and Gastrin

  • Zymogen Granules:

    • Inactive enzyme precursors

    • Require hydrolysis of an amino acid residue to become active

    • Examples:

      • Pepsinogen

      • Rennin (coagulates milk)

  • Gastrin: Hormone controlling the flow of gastric juice:

    • Components: Pepsin, Rennin, Gastric lipase, HCl, and Mucus.

Small Intestine Functions

  • Functions:

    • Enzymatic digestion (proteins, carbohydrates, lipid)

    • Absorption: uptake of end products of digestion

Sections of the Small Intestine

  1. Duodenum: Primary site for digestion

  2. Jejunum: Main area for absorption

  3. Ileum: Final segment

Duodenum Anatomy in Humans

  • Contains villi, intestinal glands, muscularis mucosae, and duodenal glands in the submucosa.

  • Entry point: Pancreatic and bile secretions.

Role of Villi

  • Function: Increase surface area allowing for more contact with digested food/feed.

Malnutrition and Intestinal Mucosa

  • Consequences: Malnourishment can lead to mild to severe villus atrophy affecting the efficiency of absorption.

Enzymes in the Small Intestine

  • Act on Four Substrates:

    1. Carbohydrates (monosaccharides)

    2. Proteins (amino acids)

    3. Lipids (fatty acids & glycerol)

    4. Nucleic acids (nucleotides)

Pancreas Overview

  • Structure: Comprises hepatic artery, portal vein, and common bile duct.{

  • Function: Secretes digestive enzymes and bicarbonate to neutralize gastric juice.

Enzymes from the Pancreas

  • Proteases:

    • Trypsinogen, Chymotrypsinogen, Carboxypeptidase

  • Lipase: Breaks down fat

  • Amylase: Breaks down complex carbohydrates

Enteropeptidase Function

  • Converts trypsinogen to trypsin, essential for activating other enzymes in the digestive process.

Absorption of Nutrients

  • Lipids: Long-chain fatty acids and triglycerides enter lymph ducts.

  • Carbohydrates and Proteins: Monosaccharides and amino acids enter portal vein.

Bile Overview

  • Production: Made in the liver, stored in the gall bladder

  • Function: Contains bile salts that emulsify lipids and increase lipid absorption

Bile Action on Lipids

- Emulsification process:

extFatglobule+extBilesalt<br>ightarrowextEmulsiondropletext{Fat globule} + ext{Bile salt} <br>ightarrow ext{Emulsion droplet}

Absorption Mechanisms

  1. Simple Diffusion

  2. Active Transport: Requires ATP, important for absorbing glucose and some amino acids.

  3. Protein-mediated Transport

Roles of Large Intestine

  • Functions include:

    • Water absorption

    • Waste storage

    • Fiber digestion

    • Sodium chloride absorption

Hindgut Fermenters G.I.T.

  • Describes the anatomy of hindgut fermenters, including:

    • Mouth, esophagus, stomach, small intestine, cecum, large colon, rectum

Cecum Overview

  • Importance: Blind pouch where fermentation occurs with a large microbial population to help digests undigested carbohydrates and fiber.

Cecum and Large Colon Production

  • Outputs: Short-chain fatty acids or Volatile Fatty Acids (VFA), water-soluble vitamins, and proteins are synthesized by bacteria; only VFAs and water-soluble vitamins are absorbed.

  • Energy Contribution: VFA can provide over 30% of the horse’s energy requirements.

Ceca in Avian G.I.T.

  • Comprised of two blind pouches aiding in microbial fermentation and fiber digestion.

Avian G.I.T. Anatomy

  • Components Include:

    • Beak, esophagus, crop, proventriculus, gizzard, cloaca, small intestine, and vent.

Mouth/Beak Functions in Avian G.I.T.

  • Functions: Gathers and breaks down feed; lacks teeth or lips, contains few salivary glands, and does not have a swallowing reflex.

Crop Functions

  • Role: Storage and moistening of feed; can become "impacted" causing digestive disorders.

Proventriculus Overview

  • Function: Equivalent of a glandular stomach; secretes hydrochloric acid and pepsinogen to aid in digestion.

Gizzard Function

  • Description: Muscular stomach that mechanically breaks down food with grit (sand and small stones) but does not separate the duodenum.

Small Intestine in Avian G.I.T.

  • Characteristics: Short compared to body size with enzymatic digestion and absorption.

  • Particle Size Importance: Ideal size is 1-3 mm; enzyme additions can enhance nutrient availability.

Phytate-phosphorous Binding and Digestion

  • Mechanism: Phytate can bind minerals, protein, and starch, decreasing digestibility.

  • Adding phytase to diet can aid nutrient breakdown, releasing nutrients otherwise unabsorbed.

Large Intestine in Avian G.I.T.

  • Overview: Very short compared to mammalian counterparts, primarily involved in bacterial activity, water absorption, and waste storage.

Cloaca Overview

  • Description: A common chamber for the G.I. tract, urinary tract, and reproductive system eggs laying.

In non-ruminant animals, the large intestine and ceca serve critical roles in water absorption and fermentation. Below is the specific information regarding their parts and functions:

Parts of the Large Intestine

The large intestine is generally divided into three main segments:

  1. Cecum: A blind-ended pouch located at the junction of the small and large intestines. It contains a large microbial population responsible for the fermentation of undigested carbohydrates and fiber. In hindgut fermenters like horses, the cecum is significantly enlarged to maximize energy extraction.

  2. Colon: This is the longest part of the large intestine. It is primarily responsible for the absorption of water and electrolytes (such as sodium and chloride).

    • In horses, it is subdivided into the large colon (primary fermentation site) and the small colon (fecal ball formation).

    • In most mammals, it is divided into the ascending, transverse, and descending colon.

  3. Rectum: The terminal portion of the gastrointestinal tract used for the storage of waste material before it is expelled through the anus.

The Ceca in Avian Species

Unlike most mammals, birds (avian species) typically possess two ceca:

  • Structure: These are two blind-ended pouches located at the junction where the small intestine meets the large intestine.

  • Function: They are the primary sites for microbial fermentation of fiber and the synthesis of certain water-soluble vitamins. They also aid in water absorption and the breakdown of remaining nutrients that were not captured in the small intestine.