Equine large intestine anatomy

Why do we see the GI issues we see with horses?

• horses are trickle feeders and have evolved to continuously consume grass for most of the day

• with modern domestic horses we’ve altered their natural behaviour, e.g. feeding twice a day, affecting their GIT

what are 2 challenged of a grazin diet?

• silicates in grass which are harder than enamel - wear down teeth

• cellulose and hemicellulose require microbial fermentation

what 3 things will changing the diet affect?

• number and type of bacteria

• pH and conditions for VFA absorption

• water balance

what do infrequent feeds cause (3)

• decrease pH (due to sudden increased VFA production)

• increase lactate

• large influx of water

what can changes in bacterial flora cause (3)

1. enteritis

2. colitis

3. laminitis

what can breakdown of the mucosal barrier lead to?

• septic peritonitis and death

what can changes in the water balance of the LI lead to?

• impactions

what does the structure of the equine teeth enable?

• grinding and rotational chewing movement - consider the drastic effect of there being a missing tooth

where does the first amount of liquid come from in the GIT?

• the saliva

  • important for swallowing and lubricating food and buffering stomach acidity

why can’t horses vomit?

• their muscular cardiac sphincter prevents reflux

what is an oesophageal obstruction known as?

• choke

give 3 reasons for choke

1. dry food - sugar beet

2. inadequate chewing - dental disease

3. unsuitable food

what are the 2 regions of the equine stomach?

• glandular epithelium

• squamous epithelium

what separates the two regions in the equine stomach?

• margo plicatus

function of the equine glandular epithelium?

• secretes hydrochloric acid, pepsinogen and mucous

what are stomach ulcers?

• areas where the acid from the glandular region has caused damage to the squamous epithelium

  • this occurs in particular with horses that are only fed at set times - the stomach produces acid continuously!

does the SI have a fixed position?

• no, only attached by the long mesentery, no specific position/rotation

what carbohydrate can’t be digested in the small intestine?

• fructans

• cellulose

• hemicellulose

common diseases of the equine SI? (5)

1. parasites

2. diarrhoea

3. impactions

4. twists/strangulations

5. infiltrative bowel disease

what does infiltrative bowel disease look like on an ultrasound, what can we describe it as

• where there should be smooth mucosa, there’s bumps, due to infiltration of immune cells

• it’s a malabsorptive disease

function of the caecum?

• major for microbial digestion of cellulose

• controls entry of ingesta into the large intestine

• pacemaker for peristalsis and motility of the large intestine

describe the gross appearance of the caecum?

• has sacculations and taenia

• it’s a blind ending sac which is on the ventral abdomen of the horse - the first organ you’ll find during surgery

how much water is exchanged across the large intestine a day?

• around 100 litres

with 100 litres being exchanged between the large intestine and blood stream daily, why is it not a good idea to feed a horse only a couple of times a day?

• because this causes this huge volume of water to be exchanged in a very short period of time → problems

Describe the structure of the ventral colon

• sacculations and taenial bands

why does the ventral colon have sacculations?

• to increase surface area

why does the ventral colon have taenial bands?

• important for mixing and moving the ingesta

Which parts of the colon can we visualise?

• large part = dorsal, because this has no sacculations

  • smaller part/where you can visualise the sacculations - this is where the ventral colon is

function of small colon

• storage of faeces and absorption of remaining water

concern/potential diagnostic issue with the small intestine?

• narrow diameter → can get impactions

when palpating a horse what should we feel in terms of taenia/other structures

• 2 on the caecum

• LDC and pelvic flexure is smooth

• anti-mesenteric taenial band of small colon is palpable

what are the 2 kinds of colic

• medical

• critical - often needing surgery

what are the 3 steps to approaching a colic horse?

1. history

2. physical examination

3. diagnostic techniques

what 3 main diagnostic techniques will we choose for a colic horse?

• rectal palpation

• nasogastric intubation

• abdominal paracentesis

what information do we want to gather for the colic horse in terms of history?

• diet

• anatomical predisposition

• infection

• parasites

• ulceration

• other organs/systems giving false signs of colic

what key physical examination aspects do we want to focus our physical examination on

• overall impression of horse

• demeanour

• degree of pain

• any self trauma

• abdominal distension

• posture

What aspects will we focus on in the clinical examination

1. TPR

2. pulse and mucous membranes - focusing on quality, mucous membranes, colour, refill time + digital pulse

3. GI sounds

4. abdominal distension

5. skin turgour

what additional diagnostic tests can we do, but that are not the key ones for colic?

• ultrasonography

• blood sample - hydration, infection, biochemistry, electrolytes

• faecal examination

• endoscopy

• radiograph

what should we feel per rectum examination on the LHS

• spleen

• caudal pole of left kidney

• pelvic flexure

• small colon

what should each of these feel like on rectal palpation?

• spleen

• caudal pole of left kidney

• pelvic flexure

• small colon

1. smooth, sharp border, no palpable masses

2. smooth margins against spleen

3. variable diameter, no sacculations, no taenial bands palpable, indentable contents, move across to midline

4. small diameter, two taenial bands, faecal balls

what should we feel per rectal examination on the RHS

• caecum

what should the caecum feel like on rectal palpation?

• large diameter, gas, feed, fluid contents, saculations

• caudal and medial taenial band dorsoventrally (often caudodorsal to cranioventral)

why is nasogastric tubing an option in horses?

• if horses get an obstruction → gas/fluid build up iin stomach → expansion → rupture

  • horses can’t vomit

why may we use a nasogastric tube?

1. horse unable to vomit

2. removal of liquid reflux

3. detect gastric impaction

4. relieve choke

5. administer oral fluid/treatment

what is a peritoneal tap?

• getting fluid from the space around the intestines

• may be useful in chronic colic and critical cases to gauge how the intestines are functioning

what do we analyse with peritoneal tap?

• colour

• volume

• turbidity

• total protein

• cell number and type

Which peritoneal tap sample is normal vs abnormal?

• LHS = normal = yellow/clear, transparent

• RHS = abnormal, red indicates potential necrosis/inflammation of small intestine

when may we use ultrasonography vs rectal examination?

• small horses/ponies

• foals

what information can we obtain from an ultrasound

• provides extra information in adult animals

• key diagnostic for colic - help identify enlargement of intestines

where do we listen to the gastrointestinal sounds in horses?

• on the side of the animal

  • RHS - upper and lower parts of the caecum

  • LHS - upper and lower parts

why do we need to be careful with rectal examination?

• can easily cause damage to the rectum

how do we check if there’s damage to the rectum post exam?

• check on the back of our glove

  • especially the back of our hand - as dorsal damage to the rectum is the most common