Poisonous plants

Poisonous plants
By Ali Cullum, Veterinarian, Anexa Vets Morrinsville

There are lots of plant poisons or toxins out there which can affect grazing stock. Sporidesmin, the facial eczema fungal toxin is a well-known summer and autumn poison. Hopefully all your animals are well protected with zinc. Other toxins & poisons we may see at this time of year include nitrates and endotoxins causing ryegrass staggers and facial eczema as well as acorns, macrocarpa and pine trees and garden trimmings such as oleander, yew, rhubarb, rhododendron.
What do we do about them and how do we know if we have a problem?

Acorn toxicity is seen at this time of year when the oak trees are dropping their leaves and acorns. In general cows do not eat enough acorns to be harmful. The common scenario is that calves are short of grass and are eating everything they come across, or some develop a taste for acorns. Sometimes people have problems with ryegrass staggers, choose a nice big tree to shelter the calves and restrict them under it with supplement. The calves then have a diet of supplement and acorns – oops! The tannin toxin causes kidney failure and the calves become depressed, anaemic, scour and have kidney failure. If intercepted early in the poisoning they will recover, but if later the kidney damage is irreversible. The anaemia and lethargy can be mistaken for zinc poisoning, facial eczema, worms, and theileria, so diagnosis usually requires blood and faeces samples to be taken unless the history of eating acorns is made obvious to the veterinarian.

Nitrate poisoning is an acute toxic syndrome generated under specific grass growth conditions. This is covered separately here.

Macrocarpa, Cupressus, leylandii, pinus radiata and cryptomeria trees all contain a toxin which is an abortiofacient (causes abortions) in cattle. These trees are generally not palatable, but when they are felled, fall over in storms or drop a lot of needles/leaves off during drought, they dry and become sweet and tasty (especially if there is little other food available!). The isocupressic acid causes abortions generally between 2 and 14 days after the animal has eaten the needles. The animals often have retained membranes and will be sick with uterine infections after aborting.
Oleander, yew and rhododendron all contain glycoside poisons that are very often lethal. While these plants do not taste good to cattle under normal circumstances, if dried they are like dried fruit snacks – sweet and tasty. Taking care to put garden trimmings well out of grazing stock eating zones is always a good idea.

If you have plants that you are not sure about whether your stock should eat them, ask your vet.


Date Added: Monday, 4th May 2020


Back...