Ragwort poisoning tends to be uncommon in the UK, as the fresh plant is extremely unpalatable. Cattle can, however, be tempted to eat ragwort if grazing is poor, and particularly if the plant is present in silage or hay, where it does not taste so unpleasant but retains its toxicity.
Ragwort damages the liver, and poisoning tends to be chronic, occurring over several weeks or months. Affected cattle can lose weight, show signs of jaundice, depression, diarrhoea, colic or straining, and develop a “bottle jaw” (fluid under the jaw and brisket, due to low blood protein). The damaged liver cannot process green plant chlorophyll adequately and this leads to a secondary photosensitisation, making animals very susceptible to sunburn (you may notice redness, inflammation and scabs on white areas).
The damaged liver becomes unable to process ammonia, which then builds up in the blood and affects the brain, causing neurological signs such as staggering, circling and apparent blindness, often leading to death. Treatment of affected cattle is often unrewarding, and efforts should be directed towards removing the risk of poisoning for other cattle. Horses are particularly susceptible to ragwort poisoning, whereas sheep seem to be particularly resilient.