Poisonous Plants

HORSEWEB-UK FEATURE Ragwort in flower

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.

The Common Ragwort or (Senecio jacobaea)
This is the most widespread type of Ragwort
The Marsh Ragwort or (Senecio aquaticus)
Found in wet meadows, marshland, ditches and moorland pasture
The Oxford and the Hoary Ragwort or (Senecio squalidus)and (Senecio erucifolius) These are both common in waste places and dry pastures

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.

These include:

weight loss
lack of appetite
staring coat
diarrhoea or constipation
abdominal pain
photosensitisation of non-pigmented skin (white areas)
oedema or fluid collection under the skin of the belly
jaundice

Behavioural signs can include:

excessive yawning
depression
sleepiness
restlessness and aimless wandering

In the advanced stages the horse may experience:

incoordination
circling
head pressing against solid objects
blindness
dementia
manic behaviour
convulsions
coma

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
Ragwort Rosettes

Ragwort is difficult to eradicate. It is biennial (rosette 1st year, flowering 2nd year) and seeds can lay dormant in the soil for up to 20 years. Familiarise yourself with the appearence of ragwort and check your pastures regularly. Pull up any plants and remove them from the field. (Don't forget to wear gloves to get a good grip and to prevent skin irritation) Do not leave any dead plants where animals can get to them.
Longer-term methods are to use Weedkillers. Known herbicides need to be applied in mild weather for maximum results. After application, it can take anywhere between 28 to 42 days for the plant to be destroyed and animals must be removed from the pasture during this period. Blanket treatment renders pasture unfit for grazing for weeks or months.
Most horse owners have only limited pasture and removing animals for such long periods is often not practical. Traditional weedkillers also destroy all green plant growth including grasses.
Ragwort can be spot sprayed with a selective weedkiller. This can be done all the year around but is best to spot spray when ragwort is at the rosette state - in winter months through to the end of July.

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.