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Questions and Answers
Why are cecal fermenters, like rabbits, able to subsist on a low-quality, high fiber diet?
Why are cecal fermenters, like rabbits, able to subsist on a low-quality, high fiber diet?
What is the main difference between the digestive system of cecal fermenters and ruminants?
What is the main difference between the digestive system of cecal fermenters and ruminants?
What is the purpose of coprophagy in cecal fermenters?
What is the purpose of coprophagy in cecal fermenters?
What is the main characteristic of hard feces, or fecal pellets, in cecal fermenters?
What is the main characteristic of hard feces, or fecal pellets, in cecal fermenters?
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What is the function of the cecum in cecal fermenters?
What is the function of the cecum in cecal fermenters?
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Why do cecal fermenters have a low digestibility of fiber?
Why do cecal fermenters have a low digestibility of fiber?
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What is the main difference between soft feces, or cecotropes, and hard feces, or fecal pellets?
What is the main difference between soft feces, or cecotropes, and hard feces, or fecal pellets?
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What is the advantage of having a cecum in cecal fermenters?
What is the advantage of having a cecum in cecal fermenters?
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Why do cecal fermenters produce two types of feces?
Why do cecal fermenters produce two types of feces?
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What is the main characteristic of cecal fermenters?
What is the main characteristic of cecal fermenters?
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Study Notes
Digestive Tract Physiology
- Digestion is the breaking down of large, insoluble molecules of food into simpler compounds that can pass through the mucous membrane of the alimentary canal into the blood and lymph.
- Absorption is the passage of digested nutrients through the mucous membrane.
Mechanical, Chemical, and Microbial Activities
- Mechanical activities: mastication and muscular contractions of the alimentary canal
- Chemical activities: enzymes secreted by the animal in digestive juices
- Microbial activities: bacteria, protozoa, and fungi that break down food enzymatically, especially in ruminant digestion
Nutritional Requirements and Digestive Tract Anatomy
- Nutritional requirements of animals are greatly dependent on their digestive tract anatomy and physiology.
- Livestock can be divided into three groups according to their digestive tracts: simple non-ruminants, ruminants, and non-ruminant herbivores.
Simple Non-Ruminants
- Include swine, poultry, dogs, cats, rats, and humans
- Often referred to as monogastric animals
- Have a pouch-like, non-compartmentalized stomach
- Rely on chemical digestion of food through secretion of digestive enzymes in the gut
- Little microbial digestion in any part of the gut
Functions of Each Major Segment in Simple Non-Ruminants
Oral Cavity
- Physical digestion occurs through mastication of food to smaller particles to increase surface area for exposure to digestive enzymes
- Starch is hydrolyzed to maltose by salivary amylase
Stomach
- Stores ingested feed and meters it into the small intestine in amounts that intestinal digestion can accommodate
- HCl secreted into the stomach kills most bacteria ingested with feed, hydrolyzes proteins due to its acidic pH, and activates pepsin
- Rennin is secreted in nursing animals to coagulate casein (a milk protein) to prevent rapid passage of milk out of the stomach, promoting proteolytic digestion of milk
Small Intestines
- Major site of digestion and absorption in simple non-ruminants
- Consists of three segments: duodenum, jejunum (major site of nutrient absorption), and ileum
- Pancreas serves as a major source of digestive enzymes that degrade carbohydrates, fats, and proteins
- Also secretes buffers (bicarbonates) that neutralize stomach acid
Primary Enzymes of the Digestive Tract
Carbohydrates
- Amylase (saliva and pancreas) breaks down starch, glycogen, and dextrin into maltose and glucose
- Maltase (small intestine) breaks down maltose into glucose
- Lactase (small intestine) breaks down lactose into glucose and galactose
- Sucrase (small intestine) breaks down sucrose into glucose and fructose
Fats and Oils
- Lipase (gastric mucosa and pancreas) breaks down lipids into monoglycerides, glycerol, and fatty acids
Proteins
- Rennin (gastric mucosa) coagulates milk proteins
- Pepsin (gastric mucosa) breaks down proteins into polypeptides
- Trypsin, chymotrypsin, and carboxypeptidase (pancreas) break down protein breakdown products into peptides and amino acids
- Aminopeptidase and dipeptidase (small intestine) break down peptides into amino acids
- Nucleotidase and nucleosidase (small intestine) break down nucleotides into nucleosides and phosphoric acid
Ruminants
- Have a large, compartmentalized stomach
- Microbes that inhabit the large stomach accomplish digestion, rather than enzymes produced by the animal itself
- Rumen is a fermentation vat that contains a large microbial population that ferments ingested feeds, producing energy from fermentation end products (VFAs)
Functions of Each Segment in Ruminants
Mouth and Teeth
- Absence of upper incisors, instead dental pads are present
- Large gap between incisors and molars allow cattle to harvest and chew large amounts of fibrous feeds
- Teeth are primarily for grinding, and tongue is used to gather and grasp grasses
- Saliva contains sodium bicarbonate to keep rumen at a proper neutral pH for good bacterial growth
Stomach
- Rumen is a fermentation vat that contains a large microbial population that ferments ingested feeds
- Major source of energy is fermentation end products (VFAs)
- Also produces large quantities of gases, mainly carbon dioxide and methane, which are removed by eructation
- Failure to eructate normally causes bloat
Cecal Fermenters
- Examples are rabbits
- Have low digestibility of fiber, so they adapt by selectively separating and excreting indigestible fiber and retaining more digestible non-fiber contents for fermentation in the cecum
- Produce two types of feces: hard and soft
- Hard feces consist of indigestible fiber that is rapidly eliminated
- Soft feces, or cecotropes, are cecal contents that are fermented in the cecum
- The animal utilizes cecotropes because of their nutritional value, in a process called coprophagy, which provides bacterial proteins and vitamins synthesized in the cecum
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Description
Learn about the digestive systems, breakdown of food into simpler compounds, and the process of digestion in the alimentary canal.
