Fellow blogger John Robertson runs a blog called The Poison Garden. As a man who is highly knowledgeable about plants and their poisons he is quite naturally critical of the British Horse Society's latest silly survey of yellow plants that may or may not be ragwort . He points out some interesting things about the survey
I’ll try not to repeat too much of what I’ve written before but, today, I want to concentrate on how a number becomes a statistic. The BHS press release announcing RAW says that its survey found that 75% of respondents reported seeing animals grazing in fields with the plant present or nearby. That’s fine, it is a perfectly easy to calculate number, assuming you have access to the full survey results as the BHS does.This is a very good point. It this is correct, then an awful lot of people are not even reporting the presence of ragwort. As I wrote in my posting about the silly BHS survey earlier this week, it appears that the BHS use statistics in the manner of a drunk using a lamppost, for support rather than illumination.
The problem is that the BHS tries to present that number as evidence of the spread of common ragwort and hopes to use it to build its campaign for further action against the plant. And that is when it becomes a statistic.
The introduction to the RAW survey says;
‘if you spot any ragwort (emphasis added) close to or in fields grazed by horses, cattle or sheep during Ragwort Awareness Week (22 - 29 July) do take a couple of minutes to report it to us using this survey.’
It specifically asks you to complete the survey only if you have seen what you think was ragwort. If people completed the survey as instructed, then 100% of respondents would have seen a yellow plant in or near fields with grazing animals. That only 75% did doesn’t actually mean anything, because the survey doesn’t mean anything, but, from the BHS’s spinpoint, it means ragwort is not the problem the BHS is trying to make it out to be.
He then goes on to describe a typical case of how the media treat ragwort poisoning. It is worth also pointing out that since there are many other sources of the problem chemicals in ragwort (They are found in 3% of the world's plants) even if you get an animal showing clinical signs of ragwort poisoning there is no way to certainly attribute ragwort as the cause of death.
I saw a local newspaper report about RAW including quotes from a local equestrian facility. These said that ragwort was a serious problem requiring annual control activities and that, ‘last year’ a horse at the facility had died from liver failure resulting from the ingestion of ragwort.
I am genuinely interested to hear about specific cases of liver failure in horses especially if it can be attributed to animals grazing on living plants. For that reason, I tracked down the centre concerned and ask for more information about the case. The reply I received said that they were certain that the animal had not ingested ragwort on their property but had displayed symptoms of liver failure shortly after arriving from elsewhere. In other words, they did not know whether the animal had grazed on Jacobaea vulgaris or been fed dead plant material in poorly produced conserved forage whilst in someone else’s care.
More interestingly, they also said that this incident happened ‘a few years’ ago and not last year as claimed by the newspaper.
They went on to volunteer the information that the business had been operating for 27 years, that ragwort had needed to be removed every one of those years and that they had only lost two horses to liver disease in all that time. They were adamant that neither animal had ingested living ragwort whilst in their care.
There are, I would add, many causes of liver failure in horses, and we know for example that over the five years 2006 to 2010 Liverpool University's Animal hospital treated about 18 cases of liver disease not one single case was recorded as being attributable to ragwort-like effects.