Grass sickness Flashcards
Most common age group for grass sickness
2 - 7 year olds
Can be any age
Most common time of year for grass sickness
April - July
Sometimes small peak autumn/winter
Risk factors for grass sickness
Causal agent unknown
- Likely associated with toxin
Horses on pasture
Mechanical dropping removal
Presence of domesticated birds on field
Stress
Animals in good to fat condition
Cool, dry weather, 7 to 11 degrees C
Frequent working
History of grass sickness cases on premises
What is equine grass sickness?
Generalised dysautonomia affected primarily enteric nervous system
Non GI signs aid in its diagnosis
Mainly parasympathetic NS
Acute – die rapidly
Sub acute survive >2 days
Chronic survive >7 days
A clinical diagnosis – decrease in GI motility from mouth to anus with decrease in GI secretions
Abdomen of greyhound – tucked up, rapid weight loss
Patchy sweating and muscle tremors
Discharge from nose – rhinitis ceca
Clinical signs of acute grass sickness
- Severe gut paralysis leads to signs of acute colic
- Difficulty swallowing
- Drooling saliva
- Nasogastric reflux
- Mucous coated, hard droppings – slow passage through GIT
- Muscle tremors and patchy sweating
- Tachycardia
- Usually die or euthanized within 2 days of clinical signs
Clinical signs of sub acute grass sickness
Similar to acute but less severe
Difficulty swallowing
Mild-moderate colic
Sweating, muscle tremors
Rapid weight loss
May eat small amounts
May die or euthanised within 1 week of clinical signs
Elephant on barrel appearance
Clinical signs of chronic grass sickness
More insidious onset
Mild or intermittent colic
Reduced appetite
May have difficulty eating, but salivation, gastric reflux, ileus – not major feature
Rapid and severe weight loss/emaciation
Some may recover
Grass sickness - diagnostic tests
Ileal biopsy
- Best diagnostic test
- Requires laparotomy – midline or flank
Laparotomy decreases survival
Neuronal degeneration within ganglia
Depletion of ganglia
Vacuolation
Pathology tends to localised to ileum in chronic EGS
Generalised intestinal pathology in acute diseases
Rectal biopsy 71% sensitivity, 100% specificity – negative result does not necessarily rule out disease
- Small scale experiment on this test
Grass sickness - test - phenylephrine
Phenylephrine test
Give increasing evidence of EGS
Topical application of 0.5% phenylephrine
These horses develop bilateral ptosis – drooping of eyelashes
Examine in 30 mins post administration
Reversal of ptosis after administration – positive test
Evidence of defective smooth muscle activity as a cause of ptosis
- False positives seen – normal horses can show some response to test
Grass sickness - oesophageal endoscopy
Lineal oesophageal ulcers
- Indicative of gastro oesophageal reflux
In absence of severe ileus and extensive gastric distension
Suggestive of lower oesophageal sphincter dysfunction
Many EGS horses do not have oesophageal ulcers
Grass sickness treatment
Nursing care is paramount for successful outcome
Symptomatic therapy for each individual problem
- Analgesia
Promotes voluntary feeding – reduces pain associated with swallowing and abdominal pain
Oesophageal/gastric ulceration – acid suppression and sucralfate to aid ulcers
Feeding
- Small feeds every 30-60 minutes
- Hand feeding – don’t leave horse to eat
Appetite stimulation
- Diazepam – 0.02mg/kg IV BID-TID
Nursing
- Grooming
- Access to other horses
- Rhinitis – steam, mucolytics
Prokinetics
- Cisapride has most data – no longer available
- Neostigmine
Prognosis of grass sickness
Hopeless unless chronic
