CASE NOTES

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Phalaris aquatica Sudden Death

Andrew Biddle, District Veterinarian, Northern New England RLPB

Posted Flock & Herd February 2011

Preface

I have worked as a veterinarian on Northern Tablelands in and around Glen Innes for the past 14 years during which time I have never definitively diagnosed any of the phalaris toxicity presentations.

Phalaris is extensively grown, many of the soils are cobalt deficient and plants are often stressed by lack of moisture or frosting.

I do not question that toxicity does not occur but has been limited by my abilities as a diagnostician or an equally plausible alternative diagnosis. As you read my brief literature search on the subject consider the likely alternative differential diagnoses you would consider. The list is as long as the time you have to compile it.

Plant Data

Phalaris aquatica
Affects sheep and cattle (also mention of horses in literature)

Toxin

Sudden Death
Literature gives varied accounts on the causative agent
Possibly N-methyl tyramine
Some discussion also that the toxin is nitrate
Possibly Cyanogenic

PE Like form of Staggers
If animals aren’t seen prior to death this presentation may seem to be sudden death.
Indol alkaloid methyl tyramine and ?-carboline.

Pathogenesis

- This is unrelated to the nervous syndrome (Carrigan 1990)
- Generally occurs within 24 hours of depasturing hungry sheep on a previously spelled paddock
- Toxic pastures are usually actively growing following a period of moisture stress or stunting
- Normally at the end of Summer
- More common in rotational grazing systems

Presentation

- Sheep are either found dead or suddenly collapse and die when disturbed
- Sheep have cardiac arrhythmia, respiratory distress and cyanotic mucous membranes
- If they don’t die some recover after a few minutes
- Those that survive may further succumb

Pathology

Rule out other causes of sudden death
- Nitrate/nitrite
- Blue green algae
- Cestrum
- Lupinosis
- Copper poisoning
- PK
- PEM
- Rock Fern

Management

Grazing management
- Hungry animals
- Stressed pasture

Cobalt supplementation (Windsor 2004)