Cypress poisoning

What to look for

  • Abortions in the last third of pregnancy or birth of stillborn or very weak calves
  • Cows affected by cypress poisoning very often have retained foetal membranes

Cause – a toxin in cypress tree fronds (usually Cupressus macrocarpa)

If cows in late pregnancy eat branches of cypress trees, the fronds may contain a toxic substance that reduces blood flow in the uterus and causes abortion or limits growth and viability of the unborn calf. Wilted branches are more toxic than fresh material. Pine needles from some varieties of pine trees can also have the same effect.

Animals likely to be affected

Cows in the last third of pregnancy.

Other diseases with similar signs

Other causes of late abortion in cattle.

Confirming the diagnosis

Diagnosis is usually confirmed by observing cows eating cypress fronds. There are no routine laboratory tests to confirm cypress poisoning but there are tests for other causes of late abortions. If there is no obvious history of animals eating cypress fronds, consult your vet to arrange for laboratory testing of aborted material.

Spread of the disease

The disease is caused by eating cypress branches and does not spread from animal to animal.


There are no specific treatments to reverse the effect of the toxin. Losses may continue for several weeks after the cows have ceased eating cypress fronds.

Risk factors

Allowing cows in late pregnancy, to have access to cypress trees (and pine trees). 


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