Approach to the horse with weight loss

Question 1

Why is weight loss important?

Answer 1

▪Common clinical challenge
– Potentially involving multiple body systems
– Multiple potential causes
– Often a specific diagnosis is not reached

▪ Emotive
– Weight loss or neglect?

Question 2

Mechanisms of Weight Loss

Answer 2

Reduced intake
▪Inappropriate feeding, unable to obtain feed, competition for feed,
dental disorders, dysphagia, pain, (gastric disease - has to be quite severe to cause significant weight loss as they usually maintain a decent appetite)

Reduced digestion, absorption or assimilation of nutrients
▪Dental disorders, malabsorption syndromes
▪Liver disease

Increased losses
▪Protein losing enteropathy (or nephropathy, but kidney dz in horses is very rare) ▪Sequestration to body cavity (peritonitis or pleuritis)

Increased requirements
▪Pregnancy, lactate, sepsis, neoplasia, other systemic disease

Question 3

Reduced intake due to malnutrition

Answer 3

Malnutrition
▪Uncommon in most horses presenting to veterinary surgeons (by
owners)
▪Consider failure to match requirements to intake (pregnancy, lactation)

Question 4

Reduced intake due to dental disease

Answer 4

▪Dental pain, poor dental function

Question 5

Reduced intake - causes of anorexia

Answer 5

Pain
▪Gastric disease – post prandial pain (only if severe)
▪Intestinal pain
▪Adhesions – low grade recurrent colic
▪Visceral pain – pleural/peritoneal disease
▪Severe musculoskeletal pain (e.g. laminitis)

Dysphagia
▪Pharyngeal/laryngeal dysfunction (guttural pouch disease)
▪Chronic grass sickness
▪Toxicity - e.g. lead
▪ Botulism - uncommon as don’t tend to feed silage to horses in the UK

Question 6

Intestinal disease

Answer 6

Malabsorption and protein losing enteropathies
▪Complex range of conditions which lead to reduced energy
uptake
– Parasitic disease – cyathostominosis, (large strongyles)
– Idiopathic
– Infiltrative bowel disease -> inflammation or neoplastic infiltrates

▪May also cause chronic diarrhoea
– Primary large colon dysfunction
– Abnormal energy substrates to hind gut flora
– Requires extensive pathology

Question 7

Clinical approach

Answer 7

History
▪Rule out obvious causes
▪Diet, parasites

Clinical Examination
▪BCS – genuine weight loss
▪ Oedema
▪ Fever
▪Oral/dental examination
▪Jaundice (extremely rare clinical sign)

Rectal examination

Question 8

Laboratory Testing

Answer 8

Targeted
▪Liver, renal, inflammation (acute phase proteins)

If the first set of bloods don’t give you a diagnosis, repeating the same tests more than once more rarely will
▪Reference ranges are calculated to include 95% of the normal population – i.e. in any given horse, 1 in 20 results will be “abnormal”

Abdominocentesis

Faecal worm egg count
- good to rule it out
- Tapeworms don’t produce the same type of eggs so it’s more difficult to assess their burden

Question 9

Hematology and Biochemistry

Answer 9

▪ Often non-specific signs ▪ Increased WBC
▪ Neutrophilia
– Horses generally have neutrophilia associated with parasite infection, cf other species & eosinophilia
▪ Eosinophilia
– Sometimes seen in parasite infestation
– Generalised inflammation
▪ Anaemia
– Often ‘anaemia of chronic disease’ i.e. mild
– Breed specific reference ranges
-> Cold blooded horses e.g. cobs, ponies, will have naturally lower PCV than e.g. TBs
▪ Acute inflammatory markers
– SAA
– Fibrinogen
-> SAA much more acute
-> Lag with fibrinogen ~48h after initiation of inflammation
▪ Liver enzymes

Question 10

Interpretation of serum proteins - total protein

Answer 10

▪Decreases may be masked by concurrent hypovolaemia ▪Hyperproteinaemia usually due to hyperglobulinaemia

Question 11

Interpretation of serum proteins - Hypoalbuminaemia

Answer 11

▪ Extremely rare and assume it’s a lab error until proven otherwise
▪GI loss far more common than renal
▪Effusions – peritoneal/pleural
▪Liver disease – rarely a cause
-> End stage liver disease exception for cause of hypoalbuminaemia - cirrhosis, marked reduction in liver function
-> But in this case there would usually be many other signs (other than low protein/albumin) that there’s severe liver dz

Question 12

Interpretation of serum proteins - Hypoglobulinaemia

Answer 12

▪GI loss
▪Could also occur due to severe kidney damage/loss

Question 13

Interpretation of serum proteins - Hyperglobulinaemia

Answer 13

▪(Chronic) inflammatory disease (including cyathostominosis)
▪ Neoplasia

Question 14

Interpretation of serum proteins - Hyperfibrinogenaemia

Answer 14

▪ Infection
▪ Inflammation
▪ Neoplasia

Question 15

Interpretation of serum proteins (acute phase proteins)

Answer 15

Serum amyloid A

Serum Protein Electrophoresis ▪Sensitivity 45%, Specificity 63%

alpha
▪ infection, inflammation, neoplasia (acute phase proteins)​

beta
▪ parasitism, chronic infection, neoplasia (C reactive protein)​

▪ gamma - polyclonal
▪ chronic infection, abscesses, neoplasia​

monoclonal
▪ tumours of the reticuloendothelial system

Question 16

Oral Glucose Absorption Test

Answer 16

▪With-hold food overnight
▪1g/kg in a 10-20% solution administered by nasogastric tube
▪Keep horse calm
▪Looking for partial or complete malabsorption

Normal
– looking for the blood glucose to double, or increase by 80%, in the last 90mins-2h

Question 17

Problems with the oral glucose absorption test

Answer 17

▪Does not only assess small intestinal function
–Small amount of glucose absorbed in large intestine
– D-xylose absorption test more reliable
-> Expensive
-> Not available

▪Partial malabsorption (25-80%)

▪Delayed flat curve
– Delayed gastric emptying -> less of a dramatic upwards spike in the curve
– Poorly starved
– Food in the stomach delays glucose exit from the stomach

Question 18

What to look for on intestinal US

Answer 18

▪Wall thickness
– SI wall should be ~3mm thick
– Large colon should be ~3-4mm thick
▪Lumen diameter
– Although normally look at this for colic cases rather than weight loss cases
▪ Motility
▪ Anatomy

Question 19

GI Biopsies

Answer 19

▪ Duodenal biopsy (transendoscopic)
– only get the surface, so no deep pathology will be found
▪ Rectal mucosal biopsy

Question 20

Rectal mucosal biopsy

Answer 20

▪Uterine biopsy forceps
▪Relies on extensive pathology
▪Rectal eosinophils very common
– Eosinophiliic proctitis
▪Easy to perform
▪20 - 30 cm inside rectum​
– still recto-peritoneal i.e. not in the peritoneal cavity, therefore risk of seeding infection into the peritoneum are much lower
▪Small piece of mucosa from 10-2 o’clock position
▪Submit for histology NSAID
– Flunixin meglumine
– Give as causes irritation in the area and don’t want the horse to strain

Question 21

Surgery for biopsies

Answer 21

▪Midline exploratory celiotomy
▪Flank laparotomy
▪ Laparoscopy
▪Expensive and require significant time off

Question 22

Laparotomy

Answer 22

▪Multiple intestinal biopsies can be obtained​
▪Whole intestinal tract can be examined​
▪Segmental disease such as focal eosinophilic IBD
can be resected and removed

Question 23

Common causes of weight loss

Answer 23

• inadequate nutrition
• dental problems
• parasitic
• IBD
• liver disease​

Question 24

Less common causes of weight loss

Answer 24

• peritonitis
• chronic grass sickness
• neoplasia​

Question 25

Initial diagnostic approach

Answer 25

• PE
• haematology and biochemistry
• US exam
• peritoneal fluid analysis
• OGAT
• assessment to response to non-specific therapy​

Question 26

Further diagnostic options

Answer 26

• laparoscopy
• laparotomy
  (scintigraphy)​

Question 27

Why can IBD cause malabsorption?

Answer 27

• thickening -> increases the barrier between the intestinal lumen and the blood, so nutrients have further to travel to be absorbed into the blood.

Question 28

Most common intestinal neoplasia

Answer 28

• lymphoma

Question 29

What does oedema often follow?

Answer 29

• hypoalbuminaemia

Question 30

An example of a GI condition where the horse may be pyrexic

Answer 30

• colitis

Question 31

Why can jaundice potentially be a sign of weight loss

Answer 31

• can be an indication of liver disease or that it hasn’t eaten for several days
• No bile duct so no storage of bile, if become inappetent they can become jaundice, e.g. 3d of inappetence.

Question 32

Why do an abdominocentesis?

Answer 32

• looking for evidence of neoplastic cells, inflammation, infection, peritonitis (protein in there)