Digestive Anatomy & Physiology EQS 110

LECTURE MENU 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

LECTURE MENU 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 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 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 PrinciplesDigestive Principles  Digestive FunctionsDigestive Functions  Oral CavityOral Cavity  Foregut Foregut  Esophagus Esophagus  StomachStomach  Small IntestineSmall Intestine  HindgutHindgut  Large Intestine  Cecum Cecum  Large ColonLarge Colon  Small ColonSmall Colon  Rectum & AnusRectum & Anus

Digestive Principles

DIGESTIVE PRINCIPLES Compared to other livestock, the horse has a unique anatomical digestive design that promotes their evolution as a roaming forage grazer 1.Horses are non-ruminants, herbivores! Horses are considered monogastric, meaning a single- chambered stomach Ruminant animals, such as cows, sheep, goats, have a stomach with four compartments Herbivores are plant eaters – a horse is designed to be eating forage, which can come from hay or pasture – this contains fiber

DIGESTIVE PRINCIPLES Compared to other livestock, the horse has a unique anatomical digestive design that promotes their evolution as a roaming forage grazer 2.Horses have a small stomach for its size! Remember that the original intent of the horse! The horse’s gastrointestinal anatomy is designed to be eating small amounts often

DIGESTIVE PRINCIPLES Compared to other livestock, the horse has a unique anatomical digestive design that promotes their evolution as a roaming forage grazer 3.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

DIGESTIVE PRINCIPLES Compared to other livestock, the horse has a unique anatomical digestive design that promotes their evolution as a roaming forage grazer 4.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 the forage matter through fermentation The Cecum

SELF KNOWLEDGE CHECK Horses have a multi-chambered stomach True Correct! Incorrect Horses are non-ruminant because they are monogastric (single chambered stomach) False

SELF KNOWLEDGE CHECK Horses break down forage in the hindgut False Correct! Incorrect Horses are hindgut fermenters – a population of good bugs help breakdown the tough, fibrous forage material True

Digestive Functions

DIGESTIVE FUNCTIONS The main functions of the digestive system are…  Ingest & digest food  Absorb nutrients  Facilitate defection Food is broken down (digested)…  Mechanically (ex. mouth & teeth)  Chemically (ex. stomach acid)  Enzymatically (ex. pancreas secretions)  Microbially (ex. bugs in the hindgut) Breaking down food creates energy!

FLOW OF DIGESTION Ingested food must go through each digestive structure until elimination occurs Oral Cavity 95% of feed appears in feces 72 hours after digestion EsophagusStomachSmall Intestine CecumLarge ColonSmall ColonRectum Anus A horse’s digestive system can be classified into two sections – foregut & hindgut

FLOW OF DIGESTION

Oral Cavity

ORAL CAVITY The oral cavity of the horse includes…  Lips  Mucous membranes  Soft palate  Hard palate  Tongue  Cheeks What occurs in the oral cavity is referred to as the pregastric stage Mainly mechanical & enzymatic digestion Salvia (salivary glands shown on the bottom right photo) contain various enzymes that begin the breakdown of food

Foregut

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

ESOPHAGUS It allows the food to move from the mouth to the stomach  Distal end has a one-way valve  Enters the stomach at too acute of an angle The esophagus is a soft walled, elastic muscular tube The anatomy of the esophagus makes the horse unable to vomit

STOMACH Provides only 10% of digestive capacity and holds 1 – 3 gallons The stomach begins the gastric phage of digestion By emptying 2/3 full, rapid intake of feed can cause the stomach to empty quickly before digestion occurs 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

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

SELF KNOWLEDGE CHECK Which of the following structures are secondary organs of digestion? Esophagus Small Intestine Stomach Correct! Incorrect, Try Again Liver

SELF KNOWLEDGE CHECK The stomach empties when 2/3 full False Correct! 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 True

Hindgut

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

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

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!

SMALL COLON 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

SELF KNOWLEDGE CHECK The hindgut consists of microbial digestion False Correct! Incorrect The horse is a hindgut fermenter – this means there is a large population of microbes in the hindgut that helps breakdown forage material True

SELF KNOWLEDGE CHECK Which of the following structures is at a great risk for an impaction colic due to a series of flexures? Small Colon Rectum Cecum Correct! Incorrect, Try Again Large Colon

Lecture 14 Quiz

QUIZ PASSWORD You have finished Lecture 14 – Digestive System. The password for Lecture 14 Quiz is Cecum. This password is case-sensitive, so be sure to enter it how it appears. Click the Blackboard picture below to login and take your quiz.