1. Digestive Anatomy & Physiology
EQS 110

2. The digestive system converts food to fuel for energy and performance!
Introduction
Understanding the horse’s digestive anatomy and physiology is not only essential to overall health, but performance
The digestive system converts food to fuel for energy and performance!

3. icon located on the bottom right hand side of the slide
Lecture Menu
Digestive Principles
Digestive Functions
Oral Cavity
Foregut
Esophagus
Stomach
Small Intestine
You may use the menu to the left to jump to main topics in the lecture or resume clicking your mouse or spacebar to progress through the lecture
Hindgut
Large Intestine
Cecum
Large Colon
Small Colon
Rectum & Anus
If you wish to come back to this menu at anytime during the lecture click the
icon located on the bottom right hand side of the slide

4. Digestive Principles

5. Horses are non-ruminant, herbivores!
Digestive Principles
Compared to other livestock, the horse has a unique anatomical digestive design that promotes their evolution as a roaming forage grazer
Horses are non-ruminant, herbivores!
Horses are considered monogastric, meaning a single- chambered stomach
Herbivores are plant eaters – a horse is designed to be eating forage, which can come from hay or pasture – this contains fiber, a source of energy
Ruminant animals, such as cows, sheep, goats, have a stomach with four compartments

6. Horses have a small stomach for their size!
Digestive Principles
Compared to other livestock, the horse has a unique anatomical digestive design that promotes their evolution as a roaming forage grazer
Horses have a small stomach for their size!
Remember the original intent of the horse!
The horse’s gastrointestinal anatomy is designed to be eating small amounts often

7. Water is essential for digestion!
Digestive Principles
Compared to other livestock, the horse has a unique anatomical digestive design that promotes their evolution as a roaming forage grazer
Water is essential for digestion!
Salvia, digestive juices, transportation and absorption of digestive material relies on adequate water intake
A dehydrated horse is at risk for not only decreased nutrient absorption, but gastrointestinal issues such as colic

8. Horses are hindgut fermenters!
Digestive Principles
Compared to other livestock, the horse has a unique anatomical digestive design that promotes their evolution as a roaming forage grazer
Horses are hindgut fermenters!
The horse’s hindgut contains a large microbial (bacterial) population that helps breakdown forage matter
These good bugs in the hindgut breakdown forage matter through a process called fermentation
The Cecum

9. Horses have a multi-chambered stomach
Self knowledge check
Horses have a multi-chambered stomach
True
False
Incorrect
Horses are non-ruminant because they are monogastric (single chambered stomach)
Correct!

10. Horses break down forage in the hindgut
Self knowledge check
Horses break down forage in the hindgut
True
False
Incorrect
Horses are hindgut fermenters – a population of good bugs help breakdown the tough, fibrous forage material
Correct!

11. Digestive Functions

12. Digestive Functions
The main functions of the digestive system are…
Ingest & digest food
Absorb nutrients
Facilitate defection
Food is broken down (digested)…
Breaking down food creates the energy needed for all life processes and performance!
Mechanically (ex. mouth & teeth)
Chemically (ex. stomach acid)
Enzymatically (ex. pancreas secretions)
Microbially (ex. bugs in the hindgut)

13. 95% of feed appears in feces 72 hours after digestion
Flow of Digestion
95% of feed appears in feces 72 hours after digestion
Ingested food must go through each digestive structure until elimination occurs
Oral Cavity
Esophagus
Stomach
Small Intestine
Rectum
Small Colon
Large Colon
Cecum
A horse’s digestive system can be classified into two sections – foregut & hindgut
Anus

14. Flow of Digestion
The hindgut of the horse consists of the cecum, large colon, small colon, and rectum. In the hindgut, food is primarily broken down through microbial (bacterial) digestion
The foregut of the horse consists of the esophagus, stomach and small intestine. In the foregut, food is broken down chemically and enzymatically

15. Oral Cavity

16. Mainly mechanical digestion occurs
Oral Cavity
The oral cavity of the horse includes…
Lips
Mucous membranes
Soft palate
Hard palate
Tongue
Teeth
Mainly mechanical digestion occurs
A horse’s saliva (salivary glands shown on the bottom right photo) contains only a little amount enzymes – saliva’s main role is to moisten feedstuffs to make it easier to chew

17. Foregut

18. Foregut The foregut of the horse includes:
Esophagus
Stomach
Small Intestine
These structures enable the transportation and breakdown of food as well as areas of nutrient absorption

19. Esophagus The esophagus is a soft walled, elastic muscular tube
It allows the food to move from the mouth to the stomach
The anatomy of the esophagus makes the horse unable to vomit
Distal end has a one-way valve!

20. Stomach The stomach begins chemical digestion
Provides only 10% of digestive capacity and holds 1 – 3 gallons
Empties into the small intestine when 2/3 full
This interferes with digestion and decreases nutrient absorption, which decreases the energy the horse would have received from the feed
By emptying 2/3 full, rapid intake of feed can cause the stomach to empty quickly before digestion occurs

21. Major site of nutrient absorption except for fiber
Small Intestine
Major site of nutrient absorption except for fiber
At 70 feet long, its holds 12 gallons of digestive material
The liver and pancreas assist the small intestine in secreting enzymes to breakdown nutrients
The liver and pancreas are considered secondary organs of digestion since feed does not pass through them

22. Which of the following structures are secondary organs of digestion?
Self knowledge check
Which of the following structures are secondary organs of digestion?
Stomach
Esophagus
Small Intestine
Liver
Correct!
Incorrect, Try Again
Incorrect, Try Again
Incorrect, Try Again

23. The stomach empties when 2/3 full
Self knowledge check
The stomach empties when 2/3 full
True
False
Incorrect
The horse’s stomach is very small for its size and it empties when 2/3 full. Due to this design, providing too much feed material at one time could overload the stomach and decrease nutrient digestion and absorption
Correct!

24. Hindgut

25. Collectively referred to as the large intestine
Hindgut
The hindgut of the horse includes:
Cecum
Large Colon
Small Colon
Rectum
Collectively referred to as the large intestine
The hindgut of the horse consists of microbial (bacterial) digestion to breakdown components of forage

26. cECUM
The cecum contains a microbial population that feeds on partially digested food – primarily fiber from forage
As the microbes breakdown fiber they release a byproduct that creates energy
These microbes need a specific type of environment to survive
A diet high in starches and sugars can be detrimental to hindgut health if not properly rationed
The cecum (and large intestine in general) is designed to digest fiber, not sugar and starches found in grain
Sudden changes to a horse’s diet can change the environment, causing the microbes to die

27. Large Colon The large colon continues microbial breakdown of feed
It is where food stays the longest – 36 to 48 hours
The large colon has a series of regions and flexures (turns)
Because some of these flexures are at acute angles and go upward, the horse is at great risk for an impaction (blockage) colic in the large colon, especially if dehydrated!

28. The small colon is responsible for extracting water from waste
Once feed material has reached the small colon, most of the nutrients have been absorbed
What is left the horse cannot digest and is waste
By the time the food leaves it has become solid and molded into fecal balls

29. Rectum & Anus The rectum is the last part of the large intestine
It ends at the anus and allows for fecal matter to be eliminated
A rectal palpation (seen on the left) is a helpful diagnostic tool for not only digestive issues, but to check reproductive health in a mare

30. The hindgut consists of microbial digestion
Self knowledge check
The hindgut consists of microbial digestion
True
False
Incorrect
The horse is a hindgut fermenter – this means there is a large population of microbes in the hindgut that helps breakdown forage material
Correct!

31. Self knowledge check
Which of the following structures is at a great risk for an impaction colic due to a series of flexures?
Cecum
Small Colon
Large Colon
Rectum
Correct!
Incorrect, Try Again
Incorrect, Try Again
Incorrect, Try Again

32. Finish

33. Finish
You have finished the lecture – Digestive System. Be aware that there is a second lecture on this topic – Common Gastrointestinal Ailments.