Wednesday, August 03, 2011
It is known that there are at least thirty species of invertebrates which are totally dependent on ragwort as a food source. There are many other species which require its nectar and pollen. As a common plant which is a good nectar source it is often a major and important resource for many declining species. Lost of habitat in general is a major problem for UK wildlife. Moth numbers have declined by over a third over the last 30 years and a major cause of this is habitat loss. This has knock on effects on other creatures such as bats and birds which use the insects as food. When I kept bees it would have been in the nectar mix.
Common ragwort contains compounds that are poisonous to most vertebrates .These are pyrrolizidine alkaloids . These substances occur in other plants as well. In fact they occur in 3% of the world's flora. Inside the plants, they occur in a non-toxic form, but after the plant has been eaten it is first changed by the intestines and then broken down by the liver. Both these processes are necessary for toxicity. (This is also why it is not dangerous for humans to handle ragwort.) The breakdown products formed in the liver are toxic. Contrary to what is often thought by the general public, the alkaloids do not accumulate inside the body of an animal. The fact is that they are excreted in about 24 to 48 hours. It is the damage that is caused to liver cells that can, if sufficient ragwort is consumed at each dose, be cumulative to the point of death occurring.
The question then is how much needs to be consumed for an animal to be poisoned. Again research provides the answer. It has been found that is lies between 5 % and 25% of body weight for horses and cattle. For goats the figure is much higher, between 125% and 404%.
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