lecture 1 - overview of animal digestive systems

What do carnivores eat?

Animals

What do omnivores eat?

Plants and animals

What do herbivores eat?

Plants

What are simple carbohydrates?

Sugars and starches

What are complex carbohydrates?

FIbers

What are the main structural carbohydrates?

Pectin, hemicellulose, and cellulose

What is lignin?

A non-carbohydrate component of plant cell walls

Why can't mammals digest most plant fiber themselves?

Their enzymes cannot break down structural carbohydrates

How do herbivores digest fiber?

Microbes ferment it

What is sacculation?

Enlarged digestive areas that house microbes and slow passage

What does microbial fermentation produce from carbohydrates?

VFAs

What are the 3 main VFAs?

Acetate, propionate, and butyrate

What are VFAs used for?

A major energy source for herbivores

Where are VFAs absorbed?

Across the rumen or intestinal wall

What is microbial protein?

Microbial biomass that can provide protein to the animal

What are the 3 major digestive strategies?

Simple monogastric, hindgut fermentation, and foregut fermentation

What is a simple monogastric digestive system?

A system with little or no microbial fermentation

Where does most nutrient absorption occur in monogastrics?

Small intestine

What does the large intestine mainly absorb?

Water

What is hindgut fermentation?

Fermentation occurring in the cecum and/or colon

What is foregut fermentation?

Fermentation occurring before the true stomach

What is the main difference between foregut and hindgut fermentation?

-Foregut occurs before the true stomach

-hindgut occurs after the small intestine

What are examples of hindgut fermenters?

Horses, elephants, pigs, and rabbits

What is a cecal fermenter?

An animal that primarily ferments feed in the cecum

What is a colonic fermenter?

An animal that primarily ferments feed in the colon

What is a ruminant?

An animal that uses foregut fermentation and rumination

What is the rumen's main function?

Microbial fermentation

What is the true stomach of a ruminant?

Abomasum

What are the 4 ruminant stomach compartments?

Rumen, reticulum, omasum, and abomasum

What is the function of the rumen?

Ferments feed using microbes

What is the function of the reticulum?

Sorts particles and helps with rumination

What is the function of the omasum?

Filters particles and absorbs water and VFAs

What is the function of the abomasum?

Digests feed and microbes using acid and enzymes

What is a true ruminant?

An animal with four stomach compartments

What is a pseudoruminant?

An animal with three stomach compartments

Why do ruminants regurgitate feed?

To rechew and reduce particle size

What is rumination?

Regurgitating, rechewing, and reswallowing feed

Why is rumination beneficial?

It reduces particle size and increases microbial access

Where are dietary and microbial amino acids absorbed in ruminants?

The small intestine

Where are most nutrients absorbed in the small intestine?

Across the intestinal wall into circulation

What happens to microbes in the ruminant digestive tract?

They pass to the abomasum and are digested

Why are microbes important as a protein source?

They provide microbial protein to the animal

What happens to microbes in hindgut fermenters?

They are mostly excreted

How can hindgut fermenters use microbial protein?

Through coprophagy

What is coprophagy?

Reingestion of feces to recover nutrients

Which digestive strategy has fermentation before the true stomach?

Ruminant/foregut fermentation

Which digestive strategy has fermentation after the small intestine?

Hindgut fermentation

Why did herbivores evolve complex digestive systems?

To obtain nutrients from fibrous plant material

What advantage does larger body size give herbivores?

Greater food intake and digestive capacity

What happens to ruminant intake when forage is difficult to digest?

Slow passage limits intake

Why can hindgut fermenters consume more low-quality forage?

Faster passage allows greater intake

What is a major advantage of ruminant fermentation?

Efficient fiber digestion and microbial protein production

What is a major disadvantage of ruminant fermentation?

Slow passage limits intake of poor-quality forage

What is a major advantage of hindgut fermentation?

Faster passage allows greater forage intake

What is a major disadvantage of hindgut fermentation?

Microbial protein is mostly unavailable without coprophagy

How does cellulose digestion compare among animals?

Ruminants digest the most; simple monogastrics digest the least

Where does microbial fermentation contribute most energy in ruminants?

In the rumen

What is the main energy source produced by herbivore fermentation?

VFAs