DISTRIBUTION:
• Originally from the Mediterranean regions, it is an introduced species to South Africa, where it has escaped from cultivated pastures.
• Grows in disturbed places, seldom in the veld.
BOTANICAL DESCRIPTION:
General: A sparse annual tufted grass.
Leaves: The hairless leaf blade is flat and firm.
Inflorescence: A dense light green to almost white spike-like panicle. 3-Flowered flat awnless spikelets are papery and striped. Conspicuous white membranous ligule. Flowers from September - January.
TOXIC PRINCIPLE:
• Serotonin-like tryptamine alkaloids
• Structurally similar to serotonin
• Functions similarly to serotonin and catecholamines in nervous systems.
SYNDROMES:
Phalaris staggers.
SYSTEMS AFFECTED:
Central nervous system.
CLINICAL SIGNS:
Cardiac syndrome:
• Sudden collapse when excited
• Respiratory distress and cyanosis
• Arrhythmia, tachycardia, ventricular fibrillation and cardiac arrest
Nervous syndrome (Phalaris staggers in sheep):
Acute poisoning:
• Transient signs (functional problem)
Chronic poisoning:
• Slow, progressive, irreversible, fatal neurological condition
• Nervous excitation - precipitated by exercise (typical)
• Hyperexcitability
• Generalised tremors
• Incoordination, limb movement stiff, inability to bend hocks - dragging of hind legs.
• Even tetanic convulsions.
• May die or recover and walk away apparently unaffected
• If left on pasture condition worsens
• Animal becomes recumbent and show repeated clonic convulsion until death occurs
• Mortalities may even occur up to 1 week after removal
• Clinical signs may persist for 2 months (elicited by exercise).
Cattle:
Usually mild signs: Stiffness of hocks and dragging of toes.
NECROPSY:
Acute cardiac syndrome:
Signs of cardiac failure.
Chronically affected animals:
• Green-grey to blue discoloration of brain, spinal cord,
renal medulla and liver.
• Leaches into formalin after few weeks.
• Intracytoplasmic yellow brown granular pigmentation in neurons of
brain and spinal cord.
• Degeneration and necrosis of affected neurons.
TREATMENT:
• No preventative measures for cardiac form.
• Nervous form (Phalaris staggers) prevented by cobalt per os.
• Dosing weekly (28 mg/sheep).
• Heavy Co-bolusses. Co on pasture.
(Parenteral Co or Vit. B12 ineffective).
