Equine Grass Sickness Flashcards
Which country has the highest incidence of Grass Sickness in the world?
Great Britain
True or False?
Grass sickness can affect horses and ponies but not donkeys
False - affects all equidae
Which age group of horses are most likely to suffer from Grass Sickness?
2-7 year olds
Can occur in all horses from 4 months to over 20 years
One of your clients is concerned about the risk of Grass Sickness to her horses. Which season is the greatest risk period seen in?
April to July with a peak in May
Some years have a second, smaller peak in the autumn or winter
What is the causal agent of Grass Sickness?
Unknown
Likely associated with a toxin
Name 4 risk factors for Grass Sickness
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
What is Equine Grass Sickness?
Generalised dysautonomia affecting mainly the enteric nervous system
Decrease in GI motility from mouth to anus, with a decrease in GI secretions
Which nervous system is affected by Grass Sickness the most - sympathetic, parasympathetic or autonomic?
Parasympathetic - decrease in GIT motility and secretions
What are the 3 presentations of Grass Sickness?
Acute = die rapidly
Sub-acute = survive 2-7 days
Chronic = survive >7 days
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?
Equine Grass Sickness
Give 4 clinical signs of acute Grass Sickness?
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
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?
Sub-acute Grass Sickness
Very weak horses with a low head carriage and holding legs underneath them
What clinical signs might make you suspect a case of chronic Grass Sickness?
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
Name the best diagnostic test to look for Equine Grass Sickness
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
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?
Equine Grass Sickness
True or False?
Diagnosis of Grass Sickness on rectal biopsy has 100% sensitivity and 71% specificity
False - 71% sensitivity and 100% specificity
Describe how to do a phenylephrine test and what a positive test result looks like
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)
Name one positive and one negative about the Phenylephrine Test for Grass Sickness
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
What might you see on oesophageal endoscopy which suggests gastro-oesophageal reflux?
Linear oesophageal ulcers
What might suggest lower oesophageal sphincter dysfunction when doing an oesophageal endoscopy?
Linear oesophageal ulcers without severe ileus or extensive gastric distention
Why would you give a horse with Grass Sickness analgesia?
Promotes voluntary feeding as reduces pain due to dysphagia and abdominal pain from slow GIT transit
Reduces pain from oesophageal/gastric ulceration
What medication can you give to treat oesophageal/gastric ulcers?
Omeprazole - proton pump inhibitor
Sucralfate - barrier
What feeding advice will you give to owners of horses with Grass Sickness?
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
Why might diazepam be given to horses with Grass Sickness?
Appetite stimulation - doesn’t work well
