There are a large number of poisonous plants to be found throughout Britain, although their abundance
will vary greatly from place to place. Horses and ponies at pasture are often at risk, especially when grass
is in short supply. Perhaps one of the more common plants and unfortunately one of the more deadly is Ragwort
There are four different species of Ragwort, all of them equally dangerous, and they are immediately recognisable by their characteristic clusters of yellow daisy-like flowers standing between 1 foot (300 cms) to 3 feet (1 mtr) tall depending on variety, and are a common sight on horse-sick pastures.
The downy-like seeds are spread on the wind and each plant is capable of producing over 100,000 seeds from October onwards. These seeds can lie dormant in the ground for years. At flowering time between July and September fields can appear to be a sea of yellow.
All parts of the plant contains alkaloids which cause irreversible liver damage, this poison is not destroyed
by drying or storing. Fortunately the living plant tastes very bitter and horses usually avoid it.
However if grazing becomes short, they may eat significant amounts and, if it is cut and left in the field, or broken off as happens when the animals are walking or grazing through it,
it will become more palatable. It is most dangerous when baled with hay. Incorporated in hay or silage it is virtually
impossible to detect ragwort by examination and even small amounts can cause serious liver damage, although luckily
the liver can regenerate itself to some degree if caught early enough. However ragwort also reduces this ability so continued
ingestion over the winter can cause serious liver failure in spring or early summer when the sunlight becomes stronger.
Several small doses of ragwort are just as dangerous as one large one, with the toxin building up in a horse over a number of years, until eventually the level at which
symptoms start to appear is reached.
Signs of ragwort poisoning are usually difficult to detect, often the horse will look well and perform normally and only when the greater part of the liver is irrepairably damaged will clinical signs develop.
Behavioural signs can include:
In the advanced stages the horse may experience:
It is important to detect liver failure at an early stage, because serious signs only occur when more than 80% of the liver is damaged. If your horse shows skin damage which is restricted to the white areas (photosensitisation), you should consult your vet about testing for liver failure. Blood samples are useful even at the earliest stages and later a liver biopsy can reveal typical changes. Early diagnosis and treatment is essential and failure to do so can be fatal - Once the liver has failed there is little that can be done to save a horse's life.Prevention
Only buy hay from a reliable source and ask the supplier for assurance that the hay, haylage or silage contains no ragwort. If you are worried that there might be some present in your fodder then ask your vet to test a blood sample of your horse for liver damage. If detected early there is hope that your horse will return to normal.
The 1959 Weed Act classifies ragwort as injurious, so it is an offence to allow it to spread. If your neighbour has ragwort ask him to remove it before it flowers and contaminates your pasture. If he refuses then contact your local MAFF (Ministry of Agriculture, Fisheries and Food) branch as they have the power to serve a clearance notice. Contact your local authority if the hedgerows, verges, railway tracks, or public places have ragwort growing in them. It is their duty to remove it and dispose of it safely.
Other plants that cause a similar liver condition include heliotrope and the legume crotalaria, several species of which have proved their toxicity to horses in the US, Australia and South Africa. One of these species causes a disease called Kimberley horse disease.
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