Are there more dangers lurking in pasture and hay than we realise? Peter Green MRCVS reviews the latest in veterinary research

Ragwort is widely recognised as a serious threat to horses, yet it is not the only danger in pasture and hay.

A recent article by two Italian scientists took another look at the plants that have been proven to cause poisoning in horses across Europe. There are some surprises to those of us who worry about ragwort and little else.

In France and Belgium, for instance, it is not ragwort but yew (Taxus baccata) that poisons most horses. The leaves, twigs and bark are all toxic, and for a pony, the lethal dose may be as little as 200g.

Yew is also common in the UK and we are all aware that it is poisonous, but yew poisoning seems either rarely to occur or is perhaps not often recognised.

In France, the second most widely reported plant poison for horses is the white cedar tree (Thuja occidentalis), a common ornamental tree in the UK and often confused with the ubiquitous Lawson’s cypress which it resembles. It seems that in France there are confirmed cases of horses poisoned when white cedar trees are blown down in storms, or when horses have access to cut branches or prunings.

Another non-native but very widespread poisonous tree is the black locust or false acacia tree (Robinia pseudoacacia), which, the Italian scientists point out, is more poisonous to horses than to other grazing animals and for some reason seems even more dangerous to ponies than to larger equines. We have many of these trees in the UK.

The real surprise in the list of villains lurking in the grass was the inclusion of hound’s tongue (Cynoglossum officinale) on the most poisonous plant danger list. This common meadow plant is very widespread across Europe, including the UK, and most amateur botanists or country folk would recognise it.

Evidently, it contains the same sort of poisonous chemicals as ragwort and, like ragwort, it is a particular problem when it becomes tasteless in hay.

Those ancient permanent pastures, resplendent with wild flowers, herbs and all sorts may not, after all, be the best meadows from which to harvest your hay.

Ref: 23 April 2015