2: Digestive physiology of horses

Question 1

What kind of digestion to horses do

Answer 1

Monogastric, hind-gut fermenters

Question 2

What is the most significant part of the horse GI tract? Why?

Answer 2

The large intestine is 50% of the length of the small intestine (much larger than the ratio in dogs or cats)

They need to get sufficient energy from the diet that they eat

Question 3

Fiber fermentation creates what?

Answer 3

SCFA (acetate, butyrate, propionate)

Question 4

What type of fermenters are horses

Answer 4

Obligate hindgut fermenters
Large caecum for fermentation

Question 5

What is colic? Six reasons

Answer 5

Horses are fed a lot of rapidly fermentable material = a lot of gas production in the colon = colon expands and rises in the body cavity and parts of the GI tract get blocked

Reasons: gas, simple obstruction, strangulation, impaction, inflammation, ulceration

Question 6

Saliva in the oral cavity of the horse

Answer 6

Saliva secretion stimulated by mastication (intense chewing compared to dogs and cats)

Saliva contains a small concentration of bicarbonate (provides buffer against stomach acids, allows some microbial fermentation in stomach)

Horse saliva contains amylase

Question 7

How many teeth do horses have?

Answer 7

Approximately 36 total
- 12 incisors, 12 premolars, 12 molars
- May have canines and wolf teeth

Question 8

Three sections of the horse stomach, their epithelium and role

Answer 8

1. Oesophageal region: squamous epithelium
2. Fundic region: glandular epithelium
   - parietal cells secrete HCl
   - Zymogen cells secrete pepsin
3. Pyloric region: glandular epithelium
   - secretes gastrin (incretin, stimulates release of HCl and pepsinogen)

Question 9

Where does microbial fermentation occur in the stomach

Answer 9

Oesophageal and fundic regions

Question 10

Describe digesta transport through the stomach

Answer 10

Stomach is a small organ in adult horses
Most digesta passes quickly into the SI
Relative emptying time of 120 mins (fast)

Question 11

Segments of the small intestine

Answer 11

Duodenum (3m)
Jejunum (20m)
Ileum (45m)

Question 12

Small intestine is the primary site of digestion and absorption of…

Answer 12

protein, starch and fat

Question 13

Exocrine action of the pancreas

Answer 13

• secretes enzymes and bicarbonate salts into the gut
• enzymes: inactive proteases, lipases and amylases

Question 14

Endocrine action of the pancreas

Answer 14

• secretes hormones into the blood
• hormones: insulin, glucagon

Question 15

Role of the liver

Answer 15

Produce bile that continuously drains into the SI which emulsifies dietary fat and activates enzymes to aid in fat digestion

Question 16

Why is there no gall bladder in horses?

Answer 16

Don’t need to break down large amounts of fat
Continuous flow of small amount of digesta, bile does not need to accumulate in large amounts for one large meal
Gradual release of bile

Question 17

What is the caecum? Contains what? Is responsible for…

Answer 17

Start of the large intestine (very large)
Contains microbial population similar to rumen (protozoa, bacteria, other microorgs breakdown fiber)
Responsible for microbial synthesis of SCFA and protein

Question 18

Name the four large compartments and three major flexures of the large colon

Answer 18

1. Right ventral colon: sternal flexure
2. Left ventral colon: pelvic flexure
3. Left dorsal colon: diaphragmatic flexure
4. Right dorsal colon

Question 19

What is the small colon?

Answer 19

4-5m small traverse colon & distal dorsal colon that ends into the rectum

Question 20

Intestinal histology of the SI vs LI

Answer 20

SI: villus, crypt
LI: no villi, crypts are deeper

Question 21

What are the ways the intestine increases capacity?

Answer 21

Coils, folds, villi, microvilli

Question 22

Look at slides 17, 18, 19

Answer 22

DO It

Question 23

What is a peptide? consists of…

Answer 23

Chain of amino acids
N terminus, polypeptide chain, C terminus

Question 24

Name two protein digesting enzymes, their location and primary action

Answer 24

Pepsin: stomach, cleaves bonds of aromatic AA at the N-terminus
Trypsin: pancreas, cleaves peptide bonds joining basic AA

Question 25

What might be reasons for AA absorption to happen as single AA and small peptides

Answer 25

• small peptide absorption costs the same amount of energy as single AA
• transporters can only absorb certain aa; peptides are backups

Question 26

Slide 21,22

Answer 26

LOOK

Question 27

Why is brush border transport of proteins not limited in some young mammals

Answer 27

Antibodies are proteins found in colostrum that need to cross the brush border if there are no antibodies transferred via the placenta

Question 28

Most AA transport is…

Answer 28

active transport

Question 29

Slide 24-27

Answer 29

know

Question 30

Enzyme involved in fat dig/abs? Location of origin? Primary action?

Answer 30

Lipase
Pancreas
Break down triglycerides into free f.a. and monoglycerides

Question 31

How do fats get absorbed? Where do absorbed fats drain into firt?

Answer 31

Bile, emulsification breaks down triglycerides into f.a.
Lymph

Question 32

Major site of SCFA production/abs? How much energy do horses get from SCFA

Answer 32

Large intestine
50-70% of energy from SCFA

Question 33

Slides 31, 32

Answer 33

SCFA uptake*

Question 34

Three methods of SCFA uptake

Answer 34

1. Passive
2. Facilitated
3. Symporter

Question 35

What are some physiological adaptations of horses?

Answer 35

No gall bladder, LI digestion, no vomiting, colic, molars/oral cavity