Equine GIT

Question 1

What is the horses digestive system like?

Answer 1

• Horses are non-ruminant herbivores
• Evolved to digest a high fibre, low starch diet
• 65% of their digestive tract is devoted solely to the digestion of fibre.
• :-Diets low in fibre can cause digestive problems
• Small intestine is ~70 feet/21m long
• Hindgut (caecum, small colon, large colon, and rectum) is ~26 feet/~8m
• = ~100 feet/30m

Question 2

What are the two sections of the GIT?

Answer 2

1.similar to pre-caecaldigestive system of a monogastric
2.similar to the rumen in a cow
•Hind gut fermentation is a mode of digestion similar to rumination
–Populations of bacteria ferment fibre

Question 3

What is the foregut made up of?

Answer 3

• Mouth/Teeth
• Oesophagus
• Stomach
• Small Intestine

Question 4

What is the hind gut made up of?

Answer 4

• Caecum
• Large Intestine
• Rectum
• Anus

Question 5

What is the purpose of the GIT?

Answer 5

–mechanically and chemically digestfood
–allow the absorptionof food
–assist the eliminationof solid waste

Question 6

What are the functions of the mouth?

Answer 6

to chew and wet food with saliva

Question 7

What is prehension?

Answer 7

Lips, tongue and teeth grasp the food. Incisors cut off the grass
The food is moved to the back of the mouth by the tongue
The molars grind the food , and mix with saliva in preparation for swallowing

Question 8

What is mastication?

Answer 8

Mastication = lateral and vertical movement of the jaw

The chewed up food then is formed into a ball by the tongue and is ready for swallowing.
The tongue manoeuvres the food to the back of the mouth to the pharynx where it enters the oesophagus

Question 9

What is chewing?

Answer 9

•Chewing time reflects food type
•For fibrous roughages ~ 4,000 chews per kg
–1KG Hay –40 mins
–1KG Oats –10 mins

73-90 chews per min on a fibre diet
chewing is important as chewing creates saliva and this is a buffer for stomach acid

Question 10

What is saliva and what is its purpose?

Answer 10

•Produced in response to chewing
•Purpose
–Lubricant
–Buffer
–No digestive enzyme activity
•Where does it come from?
-saliva glands
•How much is produced?
-30-40litres a day on a high forage diet
-amount of saliva produced is influenced by the amount of water in their diet

Question 11

What is the role of the oesophagus?

Answer 11

•Role: To transport food from the mouth to the stomach
•A muscular tube that transports the food into the stomach
•120-150cm long
A series of muscular contractions and relaxations squeezes the food along in a process called peristalsis

Where the oesophagus joins the stomach, there is a one-way valve called the cardiac sphincter- purpose to prevent regurgitation

Question 12

What is the stomach and what is its role?

Answer 12

• Located against the diaphragm
• Size and shape of a rugby ball
• Inelastic properties of stomach wall- once full it empties
• Functions most efficiently when it is only ¾ full
• Produces acid continuously
• Transit time 20 minutes to 2-3 hours
• Is the stomach ever empty?

Question 13

What are the regions of the stomach?

Answer 13

non-glandular region - top - holding area

glandular region - bottom - food mixes with gastric juices, HCl and pepsin in funds region

Question 14

How much digestion occurs in the stomach?

Answer 14

•Little digestion occurs here
–10% of the digestive capacity of the horse
•While in the stomach:
–Food is mixed with pepsin (an enzyme utilized in the digestion of protein) and hydrochloric acid (which helps to break down solid particles).
Stomach Digestion

Question 15

What region of the stomach is more likely to suffer from gastric ulcers?

Answer 15

Most likely to get ulcers in the lower part of the top half (Non- glandular region)

Question 16

What is the small intestine and what are its three parts?

Answer 16

• Approx15-22m long, narrow diameter 7-10cm.
• Capacity ~50L ~30% of GIT digestive capacity
• Three parts: duodenum, jejunum and ileum.

Question 17

What is the role of the small intestine?

Answer 17

•Digests starches, sugars, protein and fat/oils
•Enables the food to come into contact with the gut wall for absorption.
•Absorbs most of the sugars, amino acids, fatty acids, minerals, trace elements and vitamin A, D and E.
•Transit time 45 minutes –2 hours
•No gall bladder –bile is trickled in continuously from the liver via bile ducts
•Bile salts
–emulsify fats
–neutralise the effect of the acid secretions from the stomach
–Stimulate lipase secretion from pancreas
•pH 7.4 in duodenum
–Site for mixing digestaand secretions
–Brunner’s glands produce alkaline secretions
•Jejunum –main site of absorption

Question 18

How does the small intestine absorb food?

Answer 18

•Mucosal wall of SI folded
•Villi (sites of absorption)
–~ 50% of carbohydrate absorption
–almost all amino acid absorption
•Amino acids, glucose, minerals and vitamins pass into the blood stream
•Fatty acids and glycerol pass into the lymphatic system
•Structural carbohydrates pass undigested into the LI for microbial degradation
Small Intestine Absorption
↑ surface area

Question 19

What is the role of the pancreas?

Answer 19

•Controls glucose metabolism (insulin)
•Pancreatic juice neutralises highly acidic material flowing from duodenum
•Up to 20 litres in 24 hrs
•Quadruples (X4) the volume of food already in the SI
•Enzymatic degradation of proteins, fats, starches and sugars
–Lipases
–Proteases
–Amylases

Question 20

What is the role of the large intestine?

Answer 20

•Responsible for fibre digestion (and any excess starch and sugar not broken down in the small intestine)
•7.5-8 metres in length
•Capacity > 100 litres
•Transit time 5 -48 hours.
•Absorbs water, minerals, Volatile Fatty Acids and B vitamins.
•Consists of:
–Caecum
•Large, blind comma-shaped sac almost 1 metre long which has a capacity of some 30 litres.
–Colon
–Rectum
•Digestion and absorption relies on end products of microbial fermentation

Question 21

What is the caecum and what is its role?

Answer 21

•Approximately 1m in length.
•Holds 25-30 litres.
•Main function is to break down plant material.
–Will digest soluble carbohydrate (i.e. starch from cereals) that has escaped digestion in the small intestine
•After 5 hours the digestais transported to the large intestine.

Question 22

What is the process the caecum undergoes?

Answer 22

Material passes through the small intestine in ~45 mins-2hrs

Material then passes into the caecum. This acts as a holding chamber and fermentation vat where fibrous parts of food are mixed with micro-organisms

Insoluble carbohydrates (digestible fibre) are converted to volatile fatty acids: acetic, propionic and butyric acids

Digestathen passes into the colon where the presence of bends slows passage. Then to the small colon where fecalballs are formed. Then out through the rectum.

Question 23

What is the colon and what is its function?

Answer 23

•Colon is 3-4 metres long
•Large 3-3 ½ m in length and 20-25cm in diameter.
•Small colon –3m in length and 8-10cm in diameter.
•Water and electrolytes absorbed here
•Food held up to 36-48 hours
•Presence of bends and flexures which narrow
–Slows rate of passage of digesta
–Narrow diameter –70-100mm
–Likely site of impaction colic

Question 24

What is the role of the small colon?

Answer 24

•In the small colon (anterior to the rectum), digestais rounded into soft round faeces within the sacculations

Question 25

What is the rectum?

Answer 25

•Rectum ~ 1 foot (30cm) long

Question 26

What is fermentation and where does it occur?

Answer 26

Enlarged chambers housing active populations of microbes and bacteria that breakdown food via fermentation

Question 27

What are VFA’s

Answer 27

• Acetic, Propionic & Butyric
• Absorbed through the wall of the hind-gut
• Used as an aerobic energy source (slow release)
• Hind-gut microflora require an optimum pH of 6.5
• Sodium and chloride always absorbed with VFAs –results in water absorption

Question 28

How does bacterial population effect the GIT?

Answer 28

•Numbers and types dependant on the type of feed
–Bacteria usually only ferment one type of food
–Bacteria in grain fed horses are less efficient than hay fed.
Practical Implications?
–Feed type and ratio changes

Question 29

What occurs in the digestion of the large intestine?

Answer 29

Digestion via fermentation process:
–30% of protein digestion
–15-30% soluble carbohydrates
–75-85% cell wall carbohydrates
•Protein digestion is greater in the SI
•Microorganisms utilise protein for growth
–When they die and breakdown, protein is released for use by the horse
•Micro-organisms also produce water soluble vitamins (B vitamin complex and VitC) and the fat soluble vitamin K.

Question 30

What are indicators of the digestive function?

Answer 30

•Know what’s normal for your horse
•Regular gut sounds
•Awareness of what decreases motility
•Droppings
–Form?
–Number?