Digestive Anatomy & Physiology EQS 110

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!

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

Digestive Principles

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

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

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 a process called fermentation The Cecum

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!

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!

Digestive Functions

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)

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

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

Oral Cavity

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

Foregut

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

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!

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

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

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

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

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

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!

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

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

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!

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

Finish

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