This is an article that features quotes from Professor Derek Knottenbelt whose views have a special dedicated debunking section on this website and Brigadier Paul Jepson, Chief Executive
and veterinary director of The Horse Trust.It is important to know at the begining that ragwort is the larval foodplant of the cinnabar moth. Research shows that the alkaloids in ragwort are required for the moth to be stimulated to lay its eggs on the plant (1) and also that the caterpillars require the presence of the alkaloids in order to be stimulated to feed. (2) The evidence shows quite plainly that plant is essential for the moth's survival, which is what makes the article in The Veterinary Times so astoundingly wrong.
The article starts with the following text:-
LIVESTOCK owners have to
be persuaded more firmly to
remove ragwort from their
land - and vets have a key role
in convincing them, according
to prominent equine experts.
It contains several interesting comments.
Firstly:-
Expressing concern about the
impact of the plant's toxins on
the food chain and ecosystem,
Brigadier Jepson highlighted the
decline in Cinnabar moth numbers as the incidence of ragwort
had risen. He said: "It's toxic to
the moths and it's toxic to the
birds that eat the moths - the
toxin doesn't go away. Every
bit of the ragwort plant is toxic,
including the pollen, so bees and
other insects will transfer it."
It the claim that it is toxic to the cinnabar moth is a ludicrous absurdity. This claim was also made in 2007 in a book quoting Professor Knottenbelt and in 2004 Professor Knottenbelt actually wrote an article himself where he said similar things. See Professor Knottenbelt's article in Country Illustrated magazine. This site also has a page devoted specifically to this crazy myth.See Ragwort does not poison the cinnabar moth.
The idea that some how pollen carried by bees is a risk to animals is a gross exaggeration of the toxicity of the plant. Again this site has a page explaining why small doses like this are insignificant, with scientific references of course. See Ragwort cumulative.
Another quote from the article is this. World Horse Welfare deputy chief executive Tony Tyler said:-
"Once it flowers, each plant
can produce around 200,000
seeds that are open to the elements. The seeds are airborne,
so a field of ragwort that is not
even adjoining grazing animals
still poses a very real threat."
This site has a special page on ragwort seed production.
The highest figures are given by a study published in 1957. (The reference is on the page linked to above.) It gives total seed per plant figures at 8 sites as
4,760
5,900
11,690
13,370
47,600
63,700
117,740
120,400
and reaches an exceptional experimentally induced highest figure of 174,230 with plants that have been cut down and prevented from flowering in their second year which produce more seed in the 3rd. A rather exceptional occurrence in nature.
So the 200,000 figure is wrong. An advert produced by an equine charity stating just 150,000 seeds was later banned as misleading by the Advertising Standards Authority (ASA).
It is also the case that seeds are not generally carried far on the wind. Again this site has an article on this. See ragwort dispersal
There is also this comment.
Prof Knottenbelt is developing a blood test to discover if
horses have been consuming
ragwort. To validate the test,
small amounts of ragwort need
to be fed to horses heading for
slaughter. He is seeking funding
for a doctoral researcher to help
him complete the study.
This is interesting because it would seem that the research had already been done. A doctoral researcher had published her PhD thesis in 2008. All the research seemed to confirm was that ragwort poisoning was not common. ( The details and reference are on the Country Illustrated article linked to above.)
References:
1. Pyrrolizidine alkaloids as oviposition stimulants for the cinnabar moth, Tyria jacobaeae Macel M, Vrieling K. J Chem Ecol. 2003 Jun;29(6):1435-46.
2. Gustatory responsiveness to pyrrolizidine alkaloids in the Senecio specialist, Tyria jacobaeae (Lepidoptera, Arctiidae) E. A. Bernays,T. Hartmann and R. F. Chapman Physiological Entomology Volume 29, Issue 1, pages 67-72, March 2004
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