Herbivore Digestion

Flashcards covering key terms related to herbivore digestion, including ruminants and hindgut fermenters.

Ruminants

Herbivores with a multi-chambered stomach, including cows, sheep, goats, deer, and moose.

Hindgut Fermenters

Herbivores that perform fermentation in their cecum and colon, such as horses, rabbits, and some rodents.

Pseudoruminants

Herbivores similar to ruminants but lacking an omasum, including camels and llamas.

Herbivore Diet

Characterized by high fiber content and lower nutrient density.

Equine Stomach

A single-chambered, simple stomach, often referred to as a 'composite stomach,' with glandular and nonglandular sections.

Margo Plicatus

A line separating the glandular and nonglandular sections within the equine stomach.

Nonglandular Stratified Squamous Epithelium (Equine)

The storage section of the equine stomach.

Ruminant Stomach

A single stomach composed of four distinct chambers.

Forestomach (Ruminant)

Comprises the first three nonglandular chambers of the ruminant stomach: the rumen, reticulum, and omasum.

True Stomach (Ruminant)

The fourth chamber, the abomasum, which is glandular and most similar to a monogastric stomach.

Rumen and Reticulum

Nonglandular forestomach chambers where microbial fermentation primarily occurs.

Omasum

A nonglandular forestomach chamber in ruminants that primarily absorbs water and salts.

Abomasum

The glandular 'true stomach' of ruminants, similar to a monogastric stomach, secreting pepsinogen, H+, and Cl-.

Rumen Function

Primarily responsible for microbial fermentation and Volatile Fatty Acid (VFA) production.

Rumen Location

Occupies the entire left side of the abdominal cavity, extending from the diaphragm to the pelvis when full.

Rumen Papillae

Numerous projections on the rumen mucosa that increase surface area for absorption.

Rumen Pillars

Muscular folds that divide the rumen into dorsal, ventral, and two caudal sacs.

Reticulum Features

Characterized by a honeycomb appearance and connects with the rumen.

Reticulorumen

A functional term referring to the combined rumen and reticulum, where contents readily pass between the two.

Omasum Features

Also known as 'manyplies' or 'book stomach' due to its numerous leaves that increase surface area.

Abomasum Features

The true glandular stomach of ruminants, but unlike monogastrics, it is not a primary storage compartment, with ingesta flowing constantly.

Reticular Groove (Esophageal Groove)

A structure in young ruminants that folds inward to form a tube, directing milk directly to the omasum and abomasum, bypassing the reticulorumen.

Rennin (Ruminant)

An enzyme in young ruminants that causes milk protein coagulation, prolonging its residence in the abomasum for longer pepsin exposure.

Milk Fermentation in Reticulorumen

Occurs if milk enters the reticulorumen of young ruminants, leading to lactic acid production, rumen acidification, and inhibited microbial development.

Mastication (Ruminant)

Involves a 'translation' rostrolateral movement during chewing, especially when chewing cud.

Ruminant Saliva

Produced in large quantities (e.g., up to 200L/day in adult cows), containing bicarbonate and phosphate for buffering, as well as salivary amylase and lipase.

Reticulorumen Contractions

Involve three phases: primary contractions for mixing, rumination for re-chewing, and secondary contractions (eructation) for gas release.

Rumination

The process where ingesta is moved from the reticulorumen back to the mouth for re-chewing, also known as 'chewing the cud'.

Secondary Contractions/Eructation

The process of releasing gases like carbon dioxide and methane, commonly known as 'burping'.

Reticulorumen Content Layers

Consist of a dorsal gas layer, a fibrous mat (raft), and liquid-like material (rumen liquor).

Regurgitation (Rumination)

The first step of rumination involving reticulum contraction, cardiac sphincter relaxation, and reverse peristalsis carrying the bolus to the mouth.

Reinsalivation

The process of adding more saliva to the bolus during rumination.

Remastication

The re-chewing of the bolus during rumination.

Bloat (Ruminant)

A dangerous condition in ruminants caused by a failure of eructation, leading to gas buildup, severe reticulorumen expansion, compromised blood flow, respiratory issues, and potentially death.

Rumen Fermentation Timing

Occurs before enzymatic digestion, with ingesta first passing through the reticulorumen.

Nutrient Utilization in Rumen

Nutrients are initially consumed by rumen microbes, whose waste products then serve as energy and nutrients for the ruminant.

Rumen Microbes

Include bacteria, protozoa, and fungi, whose balance is influenced by the animal's diet.

Rumen Environment

A low-oxygen environment favorable to facultative anaerobic bacteria and protozoa.

Amylolytic Bacteria

Rumen bacteria that metabolize starch and soluble carbohydrates into Volatile Fatty Acids (VFAs).

Cellulolytic Bacteria

Rumen bacteria that break down cellulose, hemicellulose, and pectin into Volatile Fatty Acids (VFAs).

Rumen Protozoa

Microbes in the rumen that produce VFAs, carbon dioxide, lactate, and hydrogen; they help slow digestion.

Rumen Fungi

Microbes with a crucial role in the breakdown of the plant cell wall.

Ruminant Carbohydrate Diet

Primarily consists of complex carbohydrates such as cellulose, hemicelluloses, and pectin, which are indigestible by mammalian enzymes.

Microbe Role in Ruminant Carb Digestion

Rumen microbes utilize complex carbohydrates for their own energy, and their metabolic waste products then serve as an energy source for the ruminant.

Microbes as Protein Source

Rumen microbes, after dying or washing away, become a significant protein source for the ruminant.

Starches/Grains (Ruminant)

Also known as concentrates, these carbohydrates undergo fermentation in the rumen.

Cellulase Enzymes

Enzymes found on the surface of cellulolytic bacteria that hydrolyze the bonds in complex carbohydrates.

Amylolytic Enzymes

Enzymes that break down starches and soluble sugars in the rumen.

End-Products of Rumen Carb Metabolism

Volatile Fatty Acids (VFAs), specifically acetic acid (acetate), propionic acid (propionate), and butyric acid (butyrate).

Volatile Fatty Acids (VFAs)

The primary energy source for ruminants, produced by microbial fermentation, with a high starch diet leading to more VFAs, especially propionate.

VFA Absorption

VFAs are absorbed across all parts of the ruminant stomach and then enter the bloodstream.

VFA's Analogy

Volatile Fatty Acids serve as the main energy substrate for ruminants, analogous to glucose in monogastrics.

Lipids in Ruminant Diet

A small dietary component that, in excess, can negatively impact appetite, reticulorumen motility, and cellulose fermentation.

Microbe Lipid Digestion

Rumen microbes hydrolyze lipids into glycerol and free fatty acids (FFAs); glycerol is fermented to VFAs, and FFAs are absorbed in the small intestine.

Rumen Protein Digestion by Bacteria

Rumen bacteria produce peptidase to break proteins into small peptide chains, which microbes then absorb, convert to amino acids for their own use, or deaminate into ammonium.

Ammonium Use in Rumen

Utilized to produce VFAs, and also serves as a source for microbes to synthesize their own amino acids from non-protein nitrogen.

Microbe Protein as Ruminant Nutrient

The protein contained within rumen microbes becomes available for traditional digestion and absorption by the ruminant upon microbial death or washout.

Ruminant Small Intestine Protein Digestion

Microbe-synthesized proteins transported to the small intestine are broken down by proteolytic enzymes, similar to monogastric digestion.

Amino Acid Absorption (Ruminant)

Amino acids are absorbed across the intestinal mucosa, enter the bloodstream, and are transported via the portal vein to the liver for protein synthesis.

Urea Production (Ruminant)

A byproduct of protein metabolism in the liver and also produced from ammonium absorbed from the rumen.

Urea Recycling (Ruminant)

Ruminants recycle urea, which returns to the rumen and saliva, where microbes utilize it to synthesize proteins.

Monogastric Urea Excretion

Urea is excreted via the kidneys in monogastric animals.

Ruminant Glucose Deficiency

Due to extensive fermentation in the rumen, very few carbohydrates reach the small intestine, making ruminants essentially deficient in direct monosaccharide absorption.

Gluconeogenesis (Ruminant)

The process by which almost all glucose in ruminants is synthesized in the liver from non-carbohydrate sources.

Propionate (Glucose Precursor)

The Volatile Fatty Acid (VFA) propionate is the primary non-carbohydrate source for gluconeogenesis in ruminants.

Propionate (Fate)

In ruminants, propionate is completely converted to glucose in the liver and does not enter systemic circulation.

Butyrate (Fate)

In ruminants, butyrate is converted to beta-hydroxybutyrate, a ketone body, in the liver and is used by most tissues for energy.

Acetate (Fate)

The most abundant VFA; it cannot be used to make glucose but can be utilized for fatty acid synthesis.

Ruminant Ascending Colon

Characterized by its composition of loops and spirals.

Horse 'Great Colon'

The largest and most complex colon among domestic animals, featuring an ascending colon that forms a double horseshoe loop with the dorsal colon positioned atop the ventral colon.

Hindgut Fermentation Timing

Occurs after enzymatic digestion, primarily in the cecum and colon.

Hindgut Fermentation Location

Takes place in the cecum and colon.

Substrates for Hindgut Fermentation

Includes structural carbohydrates, nonstructural carbohydrates (starches), and some proteins.

Small Intestine Starch Digestion (Hindgut)

Some starch digestion occurs in the small intestine of hindgut fermenters, though less efficiently than in carnivores, partly due to structural elements protecting nonstructural carbohydrates.

Hindgut VFAs

Volatile Fatty Acids produced by fermentation in the cecum and colon and absorbed through their walls.

Colon Bicarbonate Production

Glands in the hindgut fermenter's colon produce bicarbonate to neutralize acids generated by the fermentation process.

Protein Digestion (Hindgut Fermenters)

Most proteins are digested in the small intestine, though cecal microbes require a nitrogen source for their own protein synthesis.

Urea Recycling (Hindgut Fermenters)

Urea is transferred from the blood to the large intestine, where microbes utilize it to synthesize proteins.

Rumen Carbohydrate Digestion

Involves the fermentation of starches and fibers, resulting in the production of VFAs.

Rumen Fat Digestion

Includes the fermentation of glycerol by microbes, while free fatty acids typically pass to the small intestine.

Rumen Protein Metabolism

Microbes utilize amino acids for their own protein synthesis or deaminate them, leading to VFA production.

Ruminant Small Intestine Digestion

Digestion of nutrients that bypass ruminal fermentation occurs similarly to monogastrics.

Ruminant Cecum

An active digestive organ, though less developed compared to the equine cecum.

Equine Stomach Digestion

Primarily involves the action of pepsin for protein breakdown.

Equine Small Intestine Digestion

Involves pancreatic amylase for carbohydrates, pancreatic lipase for fats, and various proteases for protein.

Equine Cecum Digestion

Fibers are fermented into VFAs, and urea is recycled into the gut to provide a nitrogen source for microbial protein synthesis.