Digestive Anatomy & Physiology EQS 125

icon located on the bottom right hand side of the slide Lecture Menu 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 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

Digestive Principles & Terminology

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

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

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

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

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!

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

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

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

_____ 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

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!

Oral Cavity

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

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

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

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

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

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

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

Dental Anatomy

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!

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!

Foregut

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

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

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

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

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!

Hindgut

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

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

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!

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

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

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

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

Finish

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