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Vetdle Archive

Archive Case #218: Ovine Ryegrass Staggers

Sheep veterinary case - Easy - October 7, 2026

Clinical Clues

  1. On a late-summer farm visit, several sheep in one mob begin stumbling as they are moved towards the yards.
  2. Mustering brings on head tremors and marked incoordination; a few fall when startled.
  3. Left quietly at rest, affected sheep regain their footing and appear almost normal between episodes.
  4. Only the mob grazing a perennial ryegrass-dominant paddock is affected; sheep on another pasture remain well.
  5. Pasture examination identifies endophyte-infected ryegrass, and samples are sent for toxin analysis.
  6. Analysis finds lolitrem B at a concentration associated with toxicity, supporting perennial ryegrass staggers in this affected mob.

Diagnosis

Ovine Ryegrass Staggers

Ovine Ryegrass Staggers fits the stimulus-triggered tremors, recovery between episodes and toxic pasture result. Hypomagnesaemia and other neurological disorders remain early alternatives; a quiet examination alone cannot exclude them. Remember: Some pasture toxins cause episodic signs: ask what happens when the animals move, not only how they look at rest.

Learning review

Review the case evidence

Use the paired clues to explain how the evidence in this sheep case supports the provided diagnosis, Ovine Ryegrass Staggers, then compare your reasoning with the case explanation.

Evidence checkpoints

Clues 1-2

  1. Clue 1: On a late-summer farm visit, several sheep in one mob begin stumbling as they are moved towards the yards.
  2. Clue 2: Mustering brings on head tremors and marked incoordination; a few fall when startled.

Clues 3-4

  1. Clue 3: Left quietly at rest, affected sheep regain their footing and appear almost normal between episodes.
  2. Clue 4: Only the mob grazing a perennial ryegrass-dominant paddock is affected; sheep on another pasture remain well.

Clues 5-6

  1. Clue 5: Pasture examination identifies endophyte-infected ryegrass, and samples are sent for toxin analysis.
  2. Clue 6: Analysis finds lolitrem B at a concentration associated with toxicity, supporting perennial ryegrass staggers in this affected mob.

Self-review prompts

  1. After clues 1-2, what evidence from this sheep case shaped your initial interpretation?
  2. When you compare clues 3-4 with clues 1-2, what changed in your reasoning about Ovine Ryegrass Staggers?
  3. How do clues 5-6 align with the case explanation for Ovine Ryegrass Staggers?

Educational Use

Vetdle archive cases are educational veterinary games for diagnostic reasoning practice. They do not provide veterinary advice, diagnosis, treatment, or professional medical guidance.