Equine Toxicology Flashcards
A 7-year-old horse presents with sudden onset of dysphagia, continuous chewing movements without food, and hypertonicity of facial muscles resulting in a “smiling” appearance. The owner reports the horse has been grazing in a pasture with abundant yellow-flowered plants. What is the most likely diagnosis?
A. Tetanus
B. Botulism
C. Nigropallidal encephalomalacia
D. Equine protozoal myeloencephalitis
Answer: Nigropallidal encephalomalacia
Explanation:
Nigropallidal encephalomalacia, also known as “chewing disease,” is a neurological condition in horses resulting from prolonged ingestion of yellow star thistle (Centaurea solstitialis). Clinical signs include dysphagia, involuntary chewing motions, and hypertonicity of facial muscles, leading to a characteristic “smiling” appearance. These symptoms are indicative of damage to the substantia nigra and globus pallidus regions of the brain.
What is the primary pathophysiological mechanism underlying nigropallidal encephalomalacia in horses consuming yellow star thistle?
A. Inhibition of acetylcholine release at neuromuscular junctions
B. Degeneration of dopaminergic neurons in the substantia nigra and globus pallidus
C. Demyelination of peripheral nerves
D. Autoimmune-mediated destruction of muscle fibers
Answer: B. Degeneration of dopaminergic neurons in the substantia nigra and globus pallidus
Explanation:
Prolonged ingestion of yellow star thistle leads to selective necrosis of the substantia nigra and globus pallidus in the equine brain. This degeneration disrupts normal dopaminergic pathways, resulting in the hallmark clinical signs of involuntary chewing movements and dysphagia observed in affected horses.
Which of the following strategies is most effective in preventing nigropallidal encephalomalacia in horses?
A. Regular deworming to prevent parasitic infections
B. Vaccination against neurotoxic plant toxins
C. Ensuring pastures are free of yellow star thistle and providing adequate alternative forage
D. Administering prophylactic antibiotics during high-risk grazing periods
Answer: C. Ensuring pastures are free of yellow star thistle and providing adequate alternative forage
Explanation:
Prevention of nigropallidal encephalomalacia centers on effective pasture management to eliminate yellow star thistle and ensuring horses have access to sufficient non-toxic forage. Horses typically consume yellow star thistle when other feed sources are scarce; thus, maintaining well-managed pastures and providing supplemental feed during forage shortages are critical preventive measures.
