Essential pet advice with vet Jo Gourlay

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With spring well and truly here, many of us will be trying to make the most of our gardens which includes trimming back species such as yew. In this article we take a look at why this toxic tree can be an issue to horses when in the wild they will graze amongst plants and trees that are poisonous, carefully avoiding them with no problems, as well as discussing how to recognise yew poisoning and prevent it.

All parts of both the European yew (Taxus baccata) and the Japanese yew (Taxus cuspidata) are toxic, with the leaves even remaining so after drying and storage. For poisoning to occur often there has been a change in the horse’s circumstances such as them gaining access to churchyards or gardens where Yew is commonly found after escaping from their normal grazing. Other examples of situations where poisoning becomes more likely include; people not realising how toxic it is and carelessly putting trimmings and clippings within reach of a horse or following a storm branches falling or being blown into the field. Exhaustion can be a factor too as an individual horse may become less careful about what it eats after travelling on a long journey, especially if combined with being moved away from familiar companions and introduced to new ones. Horses that are kept on their own from a young age, or in groups only including other young inexperienced animals, are also at a higher risk, especially when moved into a new pasture. It’s thought they may have a reduced ability to avoid poisonous plants by not having experienced older animals to learn from. Another potential way for poisoning to occur is if it is inadvertently fed in forage. In isolation part of the yew may be recognised by the horse as unpalatable but if mixed up with other, more palatable, plants in hay or haylage they are less likely to notice it or be able to select round it. Any sudden reduction in forage, like after a heavy snow fall, can also force horses to consider eating plants they would normally avoid. Straight forward excessive hunger can do the same and, although this time of year the grass is growing, many horses are still lean from the winter so could be tempted by some enticing green trimmings kindly dumped under their noses.

In terms of clinical signs, very sadly, yew poisoning is often fatal so the first thing you may find is a dead horse. If alive, the signs include; in-coordination, struggling to breathe, excessive salivation, abdominal pain, trembling and weakness that progresses to convulsions and coma. The effects are usually very rapid and it’s not uncommon to still find the plant present in the horse’s mouth. For horses that do survive the recovery is often incomplete. As a teenager I had first-hand experience of this when a friend’s pony was moved to a paddock near the house to be ready for the farrier at 6am the next morning. I had the awful task of waking them to say she had died with the yew branch still hanging from her mouth. So the key message is prevention. Being aware of the proximity of any yew in relation to your grazing and remember to check new grazing, even if it’s just overnight accommodation, especially if you are moving the horse onto more barren pastures. Ensure that fencing is adequate and make sure to check both it, and the field itself, after stormy weather.