Once again I find myself expressing my honest opinions and debunking some misleading anti-ragwort propaganda. One of the problems is that there is a bubble in the equine community. Incorrect facts circulate inside this bubble and are considered correct because they have been repeated so often.
I don’t suffer from this. It was abundantly obvious that misinformation was being circulated even before I started my researches over two decades ago. I get my information from the scientific literature. As regular readers will know I have been studying the science on this for more than two decades.
Today I am debunking an article posted on Facebook by one David Marlin. He is attacking another posting made by someone else elsewhere on Facebook. I'm going through it line by line.
He starts by quoting this other article and criticising things that he thinks are wrong but where the evidence tells us something different.
Dr David Marlin
RAGWORT POISONING IN HORSES
This is unquestionably true. There is so much misinformation that there are entire blogs and websites devoted to documenting just some of it as I will show here today.
RAGWORT has been "wrongly labelled as a weed"
It is quite normal and usual for people who study wildflowers not to like them being called weeds.
There is no question at all that scaremongering exists. I’ll show examples in this posting!
Unquestionably this is true. This blog is all about it!
This is a small quote taken out of context
Now this is where the bubble comes in. Let's look at this one. Is it reasonable to say this? There will be many horse people who will say that it is nonsense of course, but actually it is not!
One of the first things to determine is how toxic the plant is, and I think it's fair to assume that what the author of the video meant is that it takes 50kg to kill a horse.
We can do this and we can go to the scientific literature. Well, there is an article in the American Journal of Veterinary Research, written by well-known ragwort toxicology experts and we find this statement
"Horses, cattle and rats are susceptible to toxicity (chronic tansy ragwort lethal dose is 5% to 25% of body weight.)"
Incidentally, tansy ragwort is just the American name for our ragwort.
A quick google, which we can assume the author of the video did gives an average horse weight of 700kg to 1000kg. For the lower figure, 5% of body weight is 35 kg and 25% is 175 kg, and the figures for the upper figure are 50 kg and 250 kg. The published research shows that this is correct!
It is a common place opinion for conservationists not to like people removing wildflowers.
These are all pearls of wisdom from some nameless "expert" from a page called WILDLIFE CONSERVATION IN THANET!
Not sure how owners who have lost horses to ragwort poisoning will feel about his comments.
It is at this point that it becomes clear that he doesn’t properly understand the issue. I’ll explain it below but how would they possibly know that they have lost horses to ragwort poisoning! People inside the bubble might believe it is easy to tell but as I will explain below it really isn’t.
SOME RAGWORT FACTS......
Of 865 liver samples received by pathology services over a 5 year period, 72 (8.3%) were found to have evidence of megalocytosis; an indicator of ragwort poisoning. This actually translates to 57 samples a year.
Hang on a minute! The maths is wrong here! 72 divided by five is 14.4 not 57!
The really crucial thing here is that megalocytosis does occur in ragwort poisoning, often known technically as Pyrrolizidine Alkaloid Toxicosis after the toxins in ragwort. BUT the important fact is that it has other causes too. Most significantly mycotoxins, toxins produced by often invisible moulds in feed.
In fact the most recent research by Professor Andy Durham in a paper on these mycotoxins in horses says,
“Liver disease is commonly encountered in equine practice both as clinical and subclinical disease. Outbreaks of hepatic disease are common and once often were suspected to be caused by pyrrolizidine alkaloid (PA) toxicosis,although more recent evidence suggests that PA toxicity is far less common than generally suspected”
REMEMBER - this is going to be a gross underestimation of the number of cases as the majority are unlikely to have samples submitted for diagnosis. Some cases will be treated, some will die, some will be euthanised without a diagnosis.
This is obviously bad thinking since we know there is no way of identifying cases with certainty.
Then there is more bad information.
In 2014 a BEVA survey reported that of 303 vets, 41% had seen at least one suspected case of ragwort poisoning in the past year. Each vet was seeing at least 2 cases per year. 49% died or were euthanised.
It is first necessary to establish what a suspected case can be. The British Horse Society actually published a case in their newsletter where they described a vet turning up to a case and pronouncing on the spot that it was ragwort poisoning without further tests at all.
An equine charity responded to me with a four letter insults on-line insisting they knew of cases based on blood tests. As an expert I can tell you these only tell you there is liver damage which has a multiplicity of causes but they had evidently, it seems, been informed by their vet that blood tests were enough.
More bad information again.
In a survey by the BHS & DEFRA in 2014, 19% of respondents knew of a horse that was susepcted[sic] to have been poisoned by ragwort, with a defintive[sic] diagnosis in 21% of those cases. It was reported that 39% died or were euthanised.
First of all let’s deal with the issue again of a claimed definitive diagnosis. As I have said the evidence is very very clear you cannot have a definitive diagnosis.
It is this bubble again. I have checked and checked. There are scientific papers going back years, one of them in the highly respected journal Nature says that poisoning by fungal toxins is “indistinguishable from ragwort.”
Secondly this survey was RIGGED. First of all there were leading questions telling people ragwort was appallingly dreadful at the beginning but worse than that there was an article in the BHS newsletter instructing people to fill in the survey AND IT GAVE THEM A CASE that they could use to justify the reply that they had heard of to use. This was the case with a vet turning up and pronouncing a diagnosis without tests which I wrote about above.
In any case knowing of a horse that had ragwort poisoning is a very poor question without proper qualification of how they knew. Was it this year or 50 years ago?
Even a few mouthfulls [sic] of ragwort will cause some degree of IRREVERSIBLE liver damage. The more that is eaten, the more the damage. Damage accumulates over time! Moore RE, Knottenbelt D, Matthews JB, Beynon RJ, Whitfield PD. Biomarkers for ragwort poisoning in horses: identification of protein targets. BMC Vet Res. 2008 Aug 8;4:30.
Regular readers will notice the name Knottenbelt. Yes this is the man who claimed it is poisoning the cinnabar moth and who claimed it was a serious problem in South Africa, where the plant has never been recorded.
This is a common claim but as I explained above the literature tells us that small doses have no effect.
As little ragwort as 1% of bodyweight can prove fatal over time - Fu, P. P., Q. Xia, G. Lin & M. W. Chou. 2004. Pyrrolizidine alkaloids - Genotoxicity, metabolism enzymes, metabolic activation, and mechanisms. Drug Metabolism Reviews 36: 1-55.
Just look at this reference! As soon as I saw it I was on the alert. I am very familiar with this paper. It DOES NOT SAY THAT! It is not about that kind of thing at all. What is going on here? Is this just carelessness or is it a deliberate attempt to mislead? In my honest opinion if someone wanted to bamboozle people with bad science this is exactly the sort of paper that would be used it is 55 pages long and full of degree level biochemistry. In fact it is worse than that I took a random sample of text and put it through something that calculates a measure of readability called the Gunning Fog Index where Fog stands for Frequency Of Gobbledegook. An index of 17 requires you to have a university degree but this actually came out at 19.5! Most people wouldn’t have a clue about what it says. The word “ragwort” does not even appear in this scientific paper!
On the basis of what I have read in over 2 decades of detailed study of what is known from the scientific literature, claiming that 1% of body weight being fatal is I something I can honestly describe as scaremongering.
The risk from ragwort poisoning is not simply from plants grazed in paddocks but from ragwort contamination of feedstuffs such as hay or haylage.
The ONLY problems are in preserved forage or where pasture is so bad that they are starved into eating the plant.
Contrary to the video, pyrrolizidine alkaloids (the toxic compounds in ragwort and other plants), are absorbed through the skin. The absorption is low, not non-existent. If you handle ragwort frequently without gloves you will develop liver damage.
Where is the evidence? First of all he overestimates the toxicity of the plant and now he is making statements of something definitely happening when there is actually no case of people being poisoned in this way in the scientific literature.
The issue here is the bubble again, believing in things in general circulation amongst horsey people rather than looking properly at the scientific literature.
If small amounts are absorbed they are not necessarily toxic in their absorbed form. They would then have to be converted into that toxic form, the first step of this usually takes place in the gut so it wouldn’t necessarily happen happen but if it did they then have to go through another step and there are several things than can happen. They can just be broken down. They can be detoxified by reacting harmlessly with other substances, which includes the one that detoxifies paracetamol. If tiny amounts arrive at the DNA molecules where harm can happen then there is a DNA repair mechanism.
There are several published scientific papers showing that animals fed only small amounts of a plant with the same toxins as ragwort had no damage to their livers!
So ragwort posoning [sic]does occur in horses. It is realtively [sic] rare, but this likely due to its removal from many areas horses and ponies graze.
"However, a justification or recommendation for relaxation in ragwort control would be a risky strategy as it is possible that the
apparently low prevalence of ragwort toxicity in horses might be as a result of generally effective pasture management that, if relaxed,
might lead to an increase in toxicity cases." Andy Durham, BSc, BVSc, CertEP, DEIM, DipECEIM, MRCVS, Liphook Equine Hospital, Veterinary Record, June 13, 2015.
Notice the use of authority to make a point all those letters after his name are used to give an air of authority. It is a big no no in science. The question to really ask is if this author is really aware of all of the falsehoods, including those in the posting I am criticising. My honest belief is that the posting I am quoting is a particularly egregious example of the common place habit of equine activists of carelessly acting in a manner that at the very best is grossly overstating the problem.
Postscript - “If you own horses, ponies or livestock you must not allow them to graze on land where you know ragwort is present” https://www.gov.uk/.../stop-ragwort-and-other-harmful…
This is another example of argument from authority a no no in scientific thinking. Regular readers will know that Defra is a lousy source of information. They once told people our native ragwort was on a list of dangerous foreign invaders. It is obvious to me as an expert that they are not experts.
"Pyrrolizidine alkaloids (PAs) constitute a class of plant toxin associated with disease in humans and animals. They are found in a wide variety of plant species in the world and it is estimated that ∼3% of the world's flowering plants contain toxic pyrrolizidine alkaloids. The toxin is present in more than 12 higher plant families, among which three families, Compositae (Asteracea), Boraginaceae, and Leguminosae (Fabaceae), contain most toxic PAs." RAGWORT belongs to the family Compositae (Asteracea). Ibanez, G. (2005) Encyclopedia of Toxicology (Second Edition) https://www.sciencedirect.com/.../encyclopedia-of-toxicology
So, MR WILDLIFE CONSERVATION IN THANET..…
So what! It isn’t an issue that they are toxic we all know that. However toxic doesn’t necessarily mean dangerous and as I have pointed out repeatedly he gets his facts wrong.
1) Please get your facts right
2) Horse owners aren't looking to pull up every single ragwort plant in existence. Only the ones in the fields where our horses and ponies graze.
This simply isn’t the case. The British Horse Society tried to legislate for control on public lands and Professor Derek Knottenbelt has been quoted repeatedly in the press saying, "It is toxic to humans, so what the hell are we doing with it in this country?"
And frankly, if we do want to remove them, that is absolutly[sic] none of your business!
Actually we have a biodiversity crisis, that with climate breakdown threatens everyone’s future. Ragwort hysteria actually effects many of the nature sites in Britain. Unless you are some kind of weird anarchist you have to expect that we have rules to live by and that conservationists will work to conserve nature. It is really unacceptable to have equine activists inventing nonsense to scare people and I really really do have good evidence of this happening.
