1. Digestive Anatomy & Physiology
EQS 125

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Your notes from EQS 110 – Basic Equine Physiology will be very helpful for this lecture – much of this information will be a review
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
Digestive Principles & Terminology
Oral Cavity
Foregut
Hindgut
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3. Digestive Principles & Terminology

4. Horses are non-ruminants, 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-ruminants, 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
Ruminant animals, such as cows, sheep, goats, have a stomach with four compartments

5. Horses have a small stomach for its 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 its size!
Remember the original intent of the horse!
The horse’s gastrointestinal anatomy is designed to be eating small amounts often

6. 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

7. 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 fermentation
The Cecum

8. Digestive Terminology
There are key digestive terms that we will be using throughout this course
Remember that the flake of hay or scoop of grain you give contains various nutrients – these nutrients need to be extracted from the feed
Digestion
The breakdown of feed into basic/usable nutrients
Can be done mechanically (teeth & tongue, chemically (acids), enzymatically (pancreas secretions), or microbially (bugs in the hindgut)
Remember, the digestive system converts food to fuel for energy and performance!

9. Digestive Terminology
There are key digestive terms that we will be using throughout this course
Absorption
The removal of nutrients from the digestive tract
Metabolism
The utilization of nutrients for body needs

10. Digestive Terminology
There are key digestive terms that we will be using throughout this course
Fermentation
Chemical breakdown of a substance by bacteria, yeasts, or other microorganisms
Occurs in a horse’s hindgut

11. Foregut vs. hindgut
In the foregut there is chemical and enzymatic digestion
In the hindgut there is microbial digestion, also called fermentation
The hindgut consists of the cecum, large colon, small colon, and rectum
The foregut consists of the esophagus, stomach, and small intestine

12. _____ is the removal of nutrients from the digestive tract.
SELF KNOWLEDGE CHECK
_____ is the removal of nutrients from the digestive tract.
Digestion
Fermentation
Absorption
Microbial
Correct!
Incorrect, Try Again
Incorrect, Try Again
Incorrect, Try Again

13. 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!

14. Oral Cavity

15. The Oral cavity The oral cavity of the horse consists of the: Teeth!
Lips
Mucous Membranes
Soft Palate
Hard Palate
Tongue
Cheeks
Teeth!
The oral cavity also contains salivary glands that produce salvia – this salvia moistens feedstuffs to make it easier to chew

16. The teeth
A horse has a wider upper jaw that allows for thorough chewing
Many say horse’s teeth are constantly growing, but they are actually constantly erupting
Permanent teeth are fully formed in the first few years of life, but most of the tooth is below the gum line
As the horse eats, the chewing surface of the tooth gets worn away and more tooth emerges or erupts from below the gum line
The tooth will erupt until there is no more, which is around 20 – 25 years of age
This is why older horses can have difficulty chewing

17. The teeth
Like humans, young horses start off with baby teeth (deciduous) or milk teeth
As the horse ages, the baby teeth will be pushed out and permanent teeth will take their place
An average adult horse will have anywhere from 36 – 44 teeth
Why a range?
Certain types of teeth may not appear in certain sexes or have been removed

18. Types of teeth Incisors Found in the front of the mouth
Used for cutting and nipping at grass, hay or grain
Horses have 6 on the top and bottom

19. Types of teeth Premolars & Molars Wolf Teeth
Also known as “cheek teeth”
Used for grinding
Will have 12 – 16 premolars, and 12 molars
Premolar
Wolf Tooth
Wolf Teeth
Also called the 1st premolar
Normally removed because of interference with the bit

20. Types of teeth
Canines
Used for fighting and serve no purpose in eating
Commonly seen in colts or geldings (due to more aggressive tendencies)
Mares may have them present
A horse may have 0 or as many as 4

21. Teeth Concerns
Dental health is extremely important when it comes to nutrition because a horse that cannot chew will not be able to breakdown its food as effectively, which can decrease nutrient absorption
Floating is a procedure that helps even out dental wear
Due to a horse having a wider upper jaw than the lower, the teeth wear unevenly
Performed by an equine dentist, the unevenness is filed, similar to filing your nails
This leads to points
These points can result in discomfort, lacerations, and inefficient chewing due to pain
A horse should have this done 1 – 2 times per year depending on age

22. Dental Anatomy

23. Self knowledge check
The horse has a wider lower jaw to allow for thorough chewing
True
False
Incorrect
The horse has a wider upper jaw that allows for thorough chewing
Correct!

24. The incisors are used for grinding feed material
Self knowledge check
The incisors are used for grinding feed material
True
False
Incorrect
The incisors are used to cut and nip grass, hay or grain. The premolars and molars are used for grinding.
Correct!

25. Foregut

26. 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

27. Empties into the small intestine when 2/3 full
Stomach
The stomach assists with digestion by secreting fluids that result in the chemical breakdown of feed into nutrients
Empties into the small intestine when 2/3 full
By emptying 2/3 full, rapid intake of feed can cause the stomach to empty quickly before digestion occurs
This interferes with digestion and decreases nutrient absorption, which decreases the energy the horse would have received from the feed

28. Major site of nutrient absorption except for fiber
Small Intestine
Major site of nutrient absorption except for fiber
Secretions from itself, as well as the liver and pancreas, also help breakdown feed further
The liver and pancreas are considered secondary organs of digestion since feed does not pass through them

29. Which is the major nutrient absorption site except for fiber?
Self knowledge check
Which is the major nutrient absorption site except for fiber?
Stomach
Esophagus
Pancreas
Small Intestine
Correct!
Incorrect, Try Again
Incorrect, Try Again
Incorrect, Try Again

30. 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!

31. Hindgut

32. 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 for absorption

33. Cecum
The cecum contains a microbial population that feeds on partially digested food – primarily fiber from forage
Fiber is very tough and dense, which is why chemicals and enzymes cannot break it down fully
As the microbes breakdown fiber they release a byproduct that creates energy
Bacteria also produce essential fat- soluble vitamins that are absorbed by the horse
These byproducts are called volatile fatty acids

34. Large Colon The large colon continues microbial breakdown of feed
Contains 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!

35. Hindgut Health
The hindgut and its microbial population need a specific environment to survive
Sudden changes to a horse’s diet can change the environment, causing the microbes to die
The hindgut is designed to digest fiber, not sugar and starches found in grains
A high grain diet can be detrimental to hindgut health if not properly rationed

36. 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 the small colon it has become solid and molded into fecal balls

37. 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

38. Which structure’s role is to absorb water?
Self knowledge check
Which structure’s role is to absorb water?
Rectum
Small Colon
Cecum
Large Colon
Correct!
Incorrect, Try Again
Incorrect, Try Again
Incorrect, Try Again

39. Finish

40. End of Lecture
You have finished Lecture 2 – Digestive Anatomy & Physiology. Complete Homework #2 prior to taking your Homework quiz in Blackboard.