Equine Grass Sickness

Question 1

Which country has the highest incidence of Grass Sickness in the world?

Answer 1

Great Britain

Question 2

True or False?
Grass sickness can affect horses and ponies but not donkeys

Answer 2

False - affects all equidae

Question 3

Which age group of horses are most likely to suffer from Grass Sickness?

Answer 3

2-7 year olds
Can occur in all horses from 4 months to over 20 years

Question 4

One of your clients is concerned about the risk of Grass Sickness to her horses. Which season is the greatest risk period seen in?

Answer 4

April to July with a peak in May
Some years have a second, smaller peak in the autumn or winter

Question 5

What is the causal agent of Grass Sickness?

Answer 5

Unknown
Likely associated with a toxin

Question 6

Name 4 risk factors for Grass Sickness

Answer 6

Horses on pasture
Mechanical droppings removal
Presence of domesticated birds on the field
Stress
Good-fat body condition score
Cool, dry weather 7-11 degrees C
Frequent worming
History of Grass Sickness on premises

Question 7

What is Equine Grass Sickness?

Answer 7

Generalised dysautonomia affecting mainly the enteric nervous system
Decrease in GI motility from mouth to anus, with a decrease in GI secretions

Question 8

Which nervous system is affected by Grass Sickness the most - sympathetic, parasympathetic or autonomic?

Answer 8

Parasympathetic - decrease in GIT motility and secretions

Question 9

What are the 3 presentations of Grass Sickness?

Answer 9

Acute = die rapidly
Sub-acute = survive 2-7 days
Chronic = survive >7 days

Question 10

You are presented with a moribund horse which is sweating and has nasal discharge. The horse has had rapid weight loss and so has a tucked-up appearance.
What is your top differential diagnosis?

Answer 10

Equine Grass Sickness

Question 11

Give 4 clinical signs of acute Grass Sickness?

Answer 11

Severe gut paralysis - acute colic signs
Dysphagia
Hypersalivation
Nasogastric reflux - due to widespread ileus
Mucous coated, hard droppings - slow GI passage
Muscle tremors
Patchy sweating
Tachycardia
Death

Question 12

You diagnose a 5 year old gelding with Grass Sickness. His clinical signs are dysphagia, mild colic, rapid weight loss, sweating and muscle tremors. He is able to eat small amounts of food. Which presentation of Grass Sickness does this horse have?

Answer 12

Sub-acute Grass Sickness
Very weak horses with a low head carriage and holding legs underneath them

Question 13

What clinical signs might make you suspect a case of chronic Grass Sickness?

Answer 13

Mild or intermittent colic
Reduced appetite
May have some dysphagia
Rapid and severe weight loss
Salivation, gastric reflux and ileus not normally there

Some may recover

Question 14

Name the best diagnostic test to look for Equine Grass Sickness

Answer 14

Ileal biopsy
Requires a midline or flank laparotomy, which then decreases survival rates
Pathology localised to the ileum in chronic cases = more focal, which may be why they survive
Generalised intestinal pathology in acute disease

Question 15

You do an ileal biopsy on a horse with rapid, severe weight loss. On histopathology you see neuronal degeneration within ganglia, depletion of ganglia and vacuolation. What is your diagnosis?

Answer 15

Equine Grass Sickness

Question 16

True or False?
Diagnosis of Grass Sickness on rectal biopsy has 100% sensitivity and 71% specificity

Answer 16

False - 71% sensitivity and 100% specificity

Question 17

Describe how to do a phenylephrine test and what a positive test result looks like

Answer 17

Apply topical 0.5% phenylephrine to one eye
Examine the eye 5 minutes later
Positive test = reversal of the ptosis in that eye (increase in angle between the corneal surface and the eyelash)

Question 18

Name one positive and one negative about the Phenylephrine Test for Grass Sickness

Answer 18

Positive - helps support the theory that defective smooth muscle activity is an underlying cause of ptosis

Negative - some false positives seen as normal horses can show some response to this test

Question 19

What might you see on oesophageal endoscopy which suggests gastro-oesophageal reflux?

Answer 19

Linear oesophageal ulcers

Question 20

What might suggest lower oesophageal sphincter dysfunction when doing an oesophageal endoscopy?

Answer 20

Linear oesophageal ulcers without severe ileus or extensive gastric distention

Question 21

Why would you give a horse with Grass Sickness analgesia?

Answer 21

Promotes voluntary feeding as reduces pain due to dysphagia and abdominal pain from slow GIT transit
Reduces pain from oesophageal/gastric ulceration

Question 22

What medication can you give to treat oesophageal/gastric ulcers?

Answer 22

Omeprazole - proton pump inhibitor
Sucralfate - barrier

Question 23

What feeding advice will you give to owners of horses with Grass Sickness?

Answer 23

Small feeds every 30-60 minutes
Hand feeding - don’t leave the horse to eat
Hand-grazing - makes the horse move so the GIT mobilises
Varied diets

Question 24

Why might diazepam be given to horses with Grass Sickness?

Answer 24

Appetite stimulation - doesn’t work well

Question 25

What nursing actions may help a horse with Grass Sickness?

Answer 25

Grooming
Access to other horses
Rhinitis - steam and mucolytics

Question 26

What prokinetics might be beneficial for a horse with Grass Sickness?

Answer 26

Cisapride has most data but no linger available
Neostigmine

Question 27

How long does the average horse take to return to work after chronic Grass Sickness?

Answer 27

Around 11-12 months

Question 28

Which ganglia can be used to diagnose Equine Grass Sickness?

Answer 28

Cranial mesenteric ganglia
Cranial cervical ganglia

Question 29

A client is concerned about the risk of Equine Grass Sickness to her horses. What preventative measures can you advise?

Answer 29

Stable horses in spring and early summer in areas where disease is prevalent (reduces risk)
Stable horses in affected areas when dry weather 7-11 degrees C is present for 10 days
Stable new horses in affected areas
Graze affected fields by other stock in spring and summer
Move other horses out of a field if several horses affected in a group, unless this is too stressful