Equine GI Flashcards
1
Q
Broadly describe differences in ascending, transverse and descending colon between species
A
- Ascending smallest section = modified
2. T and D = largely similar
2
Q
Describe the functional anatomy of the equine GI
A
- Ascending colon vastly modified into a fermentation chamber
- 3 compartments which are separated by physiological valves
- different types of fermentation occurs in each compartment
- compartments: Caecum, ventral colon, dorsal colon
- relatively short transverse colon narrows to meet descending colon
- Longitudinal muscle not continuous strand but arranged into taeial bands - diff number in each part
3
Q
Name the valves and where they are in the equine large intestine
A
Ileum 1. ileo-caecal valve Caecum 2. caeco-colic valve Ventral colon 3. narrow pelvic flexure dorsal colon 4. Narrowing transverse colon
4
Q
In horse what is unique about the caecum?
A
- ileum f SI goes INTO caecum in other species caecum is plopped on the side
5
Q
Fermentation of non hydrolysable CHO in horse
- What does it depend on?
- How different to cow
- microbial products
- positioning of LI means what?
A
- degree/ type depends on material reaching large intestine (like cow)
- But SI before fermentation in H, cow = other way around
- vast majority/all of non-hydrolysable CHO reaches large intestine so fermentation extensive
- Microbial products of fermentation are VFAs / CH4 / CO2
• Large intestinal mucosa can absorb these VFAs
• Gases passed to rectum by peristalsis and expelled (flatulence) - Microbial balance easily upset, just as in ruminants – diarrhea and acidosis
- As large intestine is terminal part of GI tract some VFAs AND ALL microbial protein egested / wasted
• Rabbits / rats practice coprophagy to avoid this waste (some sick horses can do)
6
Q
What about fermentation in carnivores?
A
- Most digestion/ absorption has already occurred prior to large intestine therefore fermentation is minimal
7
Q
Equine colic
A
- Colic is not a disease but a clinical sign of abdominal pain
- True colic relates to gastro-intestinal pain
- False colic relates to other abdominal organ pain (e.g. bladder, kidney, uterus, foal etc)
- Colic results in the highest levels of equine morbidity & mortality therefore an accurate diagnosis is essential in order to treat successfully
- The most useful procedure in diagnosis of colic is rectal examination
8
Q
Metabolism of VFA in equine GI
A
- similar to ruminants = used as an energy source
9
Q
What are the main VFAs
Improtance of one?
A
acetate, propionate and Butyrate. Can only generate glucose from propionate!
10
Q
How is Acetate used?
A
- used in liver
- oxidised in most other cells to generate ATP
- Major source of acetly CoA for lipid synthesis
11
Q
How is Propionate used?
A
- Substrate for gluconeogenesis
12
Q
How is Butyrate used?
A
- Energy production
2. Cellular homeostasis
13
Q
Absorption of VFAs
A
- (acetate, propioante, butyrate) absorbed by short chain fatty acids/ in exchange for HCO3- - this helps control pH
- VFAs absorbed intact rather than metabolised as they’re absorbed like with R
- propionate = gluconeogenesis to produce glucose
14
Q
What is another name for VFA
A
short chain fatty acid
15
Q
Absorption of Na
A
- Absorbed by sodium channels & Na+/H+ exchanger (NHE transporter)
- Sodium absorption enhanced by aldosterone
16
Q
Absorption of Cl-
A
• Absorbed by bicarbonate / hydroxyl exchange
17
Q
Absorption of water
A
- Most of rest of water passing from SI absorbed in large intestine
- Osmotic pressure
- Hydrostatic pressure
- Solvent drag
- Extensive re-absorption in horses – 100s of litres
18
Q
Water absorption in horse vs most animals
A
- SI is where main water re absorption occurs (70-80%)
- Horse LI still absorbs some but most water is secreted into SI so most occurs here
- by same process
19
Q
COMPARATIVE PHYSIOLOGY
A
- Large intestine physiology similar in most domestic species EXCEPT horse
- In feral horse on diet of grass 75% energy derived from VFAs produced by microbial fermentation in the hind-gut
- Fermentation similar process to that occurring in ruminant fore-stomach
- EXCEPT small intestine occurs before fermentation vessel
- In ruminants any hCHO immediately fermented so none passes into SI
- However in horse potentially lots of hCHO can pass into LI if overload of SI capacity to digest / absorb it can upset microbial populations
20
Q
CARBOHYDRATE FERMENTATION
A
- Fibre (containing β-glycosidic bonds) requires microbial fermentation
- Products of fermentation are principally VFAs
- VFAs cause a decline in pH of luminal contents - acidic
• Neutralised by copious pancreatic secretion containing HCO3-
• Goblet cells in large intestine secrete mucous & HCO3-
• Ileum also secretes HCO3- - If production of VFAs excessive H+ ions too numerous to be neutralised by HCO3- secretions
• pH of luminal contents declines
• Favours multiplication of acid resistant microbes (amylolytic bacteria / lactate producers)
• Lactic acid poorly absorbed cf VFAs causing further pH decline
21
Q
PROTEIN FERMENTATION
A
- Probably similar to ruminants
- HOWEVER
• Equine hind-gut (LI) more capable of absorbing amino acids / peptides
• Hence less amino acids / peptides taken up by microbes, more being absorbed by the host
• This is a good thing as (all) microbial protein is lost in faeces in hind-gut fermenters
• Microbial nitrogen requirements satisfied by urea secreted by ileum / large intestine
Broken down by microbial urease into NH3 to be used as NPN source for microbial protein synthesis
22
Q
WATER ABSORPTION
A
- Compared to other species more water reabsorption occurs in large intestine
- At luminal pH (6.5) most VFAs in ionic form which are poorly absorbed
- Local mechanism of secretion of H+ in exchange for Na+ converts ions to their respective acids thus enhancing their absorption
- When VFAs absorbed there is also a net absorption of NaCl which enhance water reabsorption via osmotic pressure & solvent drag – inc efficiency
- HCO3- secreted in exchange for Cl- maintain pH at level suitable for fermentation
23
Q
FOREGUT VS HINDGUT FERMENTATION efficiency
A
- Hind-gut fermentation 70% as efficient as fore-gut fermentation. Ruminant = 90%
- Microbes less efficient lower prop of amyloytic fermenters
- Hind-gut fermenters lose microbial protein in faeces
- Coprophagy - rabbits / rodents eat certain component of their faeces high in microbial protein
24
Q
Gut transit time fore gut vs hind
A
- gut-transit time in fore-gut fermenters dependent on rate of fermentation and can’t be reduced whatever the nutrient quality of the fibre
• Horses on poor quality forage can decrease gut transit time and therefore consume more
• Ruminants more efficient on good quality forage
• Horses more efficient on poor quality forage as long as it’s in abundance
25
What is the main neutralised of VFAs decreasing pH in foregut vs hind gut
1. foregut = mainly saliva
| 2. hind = copious pancreatic secretion containing HCO3-
26
Acidosis in horses
1. Too high level of hydrolysable CHO
2. Amylolytic poliferate at expense of cellylolytic
3. A = rapid fermentors = inc VFA
4. also favours lactate producers
5. both lactate p and amylolytic bacteria are acid resistant
6. LActic acid poorly absorbed = further pH decline
27
Where does most water reabsorption occur?
1. Caecum
2. ventral colon
in particular
28
Microbiology:
| Bacteria
Similar categories to ruminants
1. horses tend to have less amylolytic (rapid fermenter) and more celluloytic (slow fermenter) = overall F = slwoer process
29
Microbiology: Protozoa
1. contribution unknown as if removed v little difference
| 2. Protozoa lost in faeces therefore can’t be digested as in ruminant
30
Microbiology: Fungi
* Probably similar to ruminants
| * Split apart lignin thereby rendering it susceptible to digestion by celluloytic bacteria
31
Motility - why slow?
| Different in hind and fore gut time
* Large intestinal transit time must be slow enough to allow fermentation to occur
* Hind-gut fermenters - several days
* Fore-gut fermenters - 24 hours
32
Caecum adn colon, most species vs horse
* In most species caecum & colon form continuous compartment – pelvic flexures slows
* In horses caecum separated from colon by caeco-colic valve
* Separate fermentation compartment with no retrograde flow of material from colon to caecum
33
Point of caecum
Reserve capacity to allow food to pass back into it
1. main reason to slow down rate of fermentation, must have peristalsis occurring
2. food moving backwards = slows down
3. In most animals it can't go back into illeum due to physiological valve
4. If caecum didn't exist it would cause distension of gut = pain = not contribute to normal digestive process of animal
34
Horse caecum contractions
| What is the point
MAss movement occur ev 3-5 mins extra as well as peristalsis, antiperistalsis, segmental contractions
1. empty all contents into ventral colon
35
How to tell if healthy
should hear toilet flushing sound every 3-5 mins on RHS = caecal contraction
36
Colonic contractions in most species:
1. Main = segmental, peristaltic and anti p
2. Anti p contractions are more prominant in proximal colon
3. Retrograde movement of chyme from colon into caecum NOT into ileum
37
Colonic contractions in horse
1. NO retrograde movement from colon into caecum - once emptied caeco-colic valve SHUT
2. reverse P in distal ventral colon not proximal like in other species
3. Slow movement of passage fo chyme from ventral to dorsal colon via pelvic flexure
4. Only small particles/ well fermented material can pass via pelvic flexure into dorsal colon
5. Ensures slow enough transit time to allow efficient fermentation
38
How to diagnose Equine colic
1. REctal examination
| 2. Abdomincal Auscultation
39
How many ribs in horse
18 pairs
40
Normal sound of horse gut on LHS
1. Left dorsal = SI and small colon (descending)
Fluidy in nature, higher pitch
2. Left ventral = pelvic felxure
41
Normal gut sounds on RHS
```
1. R dorsal/ ventral = caecum
Loud sound, like toilet flushing = emptying via caeco-colic valve
3-5 per 5 min
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42
Abnormal sounds
1. Inc frequency = enteritis, spasmodic colon
2. Tympanitic = gut distension with gas, obstruction
3. Decreased frequency = ileus, obstruction
