Beware of poisonous plants for livestock

Vet's vision
with Phil Rennie
Tauranga Vets

Sporadically during most years vets are called to investigate sudden illnesses and unexpected deaths in otherwise healthy animals. While they can occur at any time of year, summer is more common for poisonings as feed supplies shrink and hungry animals becoming less discerning with their diets.

Hot, dry summer conditions are present throughout much of New Zealand as we head into this New Year, so once again we’re likely to see an increase in plant poisonings. Other factors include stress on pasture and crop species, proliferation of weed species, fruiting and seeding of trees and shrubs and dumping of garden waste in paddocks.

Often, where no obvious sign of infection or trauma has occurred to the animals, we need to look at intoxication as the cause of the symptoms. While not exhaustive, in the next two editions I’ll cover some of the main plants known to be lethal to livestock.

Acorns/Oak (Quercus spp)

Fallen acorns and branches are sources of toxin, being most poisonous when green. Cattle and sheep are vulnerable, with young stock more susceptible than adults. Affected individuals show lethargy, anorexia and wasting with frequent urination.  

Avocado (Persea americana)

All parts of the plant are toxic. A wide range of livestock are affected with goats and horses being most sensitive. Signs of intoxication include lethargy, respiratory distress, swelling, cyanosis, cough, exercise intolerance and death from heart failure. Horses may develop edema of the head, tongue, and brisket. The toxin persin also produces a sterile mastitis in lactating animals.

Bracken Fern (Pteridium esculentum)

Toxicity occurs with grazing scrubby areas and rough pasture sward. Cattle, goats and horses can be affected. Various forms of disease can develop including bladder bleeding with discoloured urine, bowel tumour growths and neurological staggers.

Foxglove (Digitalis spp)

Sporadic consumption of these colourful flowers can occur by accident in gardens, on roadsides, in pastures and bordering bush. Although very bitter in taste and therefore not being very palatable, inquisitive young horses and cattle can be affected. The toxin digoxin causes heart failure preceded by drooling, weakness, collapse and seizures.


Karaka (Corynocarpus laevigatus)

Accessed by stock near bush blocks when grazing scrubby or bush areas and transporting stock along roadsides. As well as livestock it can also affect people and dogs. The toxin karakin affects the body’s energy supply, interfering with the Krebs cycle, which results in profound lethargy and collapse with neurological and muscular distress preceding death.

If you have any questions about possible toxins on your property, contact your local vet, before running the risk of exposing stock to the source. Vets are well placed to investigate any suspicious cases and help to prevent future poisonings. Next month, I’ll detail some more plants that are a threat to poisoning livestock.


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