Equine vet gets it wrong on ragwort.

 Today I am once again going to talk about my honest opinions on ragwort. It includes an example of a discussion where an equine vet got things wrong on ragwort. This happened on Facebook earlier in the week and I have given her enough time to respond so I think I should now share this encounter so that you can all see the problem.

As regular readers will know it isn't the first time there has been an issue with what an equine vet has said. I do wonder if they are taught all I would expect them to be taught. 

The issue in question here is whether you can diagnose ragwort poisoning with certainty. My view on this is, after having read the literature,  you cannot. It is quite simple really. There are characteristic symptoms of damage which can be observed under a microscope, but while those symptoms are characteristic of pyrrolizidine alkaloid poisoning caused by the toxins in ragwort, that is not their only cause. Another cause is damage by toxins produced in invisibly mouldy hay.

Since you have more than one cause it is surely not possible to say that the damage is caused by one of them.

Although it doesn't seem to be the problem in this specific case there is also the issue of vets doing blood tests which are just indicative of liver damage from any of a number of causes.  I got four letter insults from one equine charity which insisted that veterinary blood test results proved ragwort poisoning on twitter.

Naturally as a specialist on ragwort I do keep up on the latest scientific literature if I can and there is a paper published just last month that contains some interesting quotes.

"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."

 Pyrrolizine alkaloid toxicosis is what happens in ragwort poisoning so the recent evidence suggests it is far less common than had been assumed. I've explained the exaggerations and nonsense statistics in previous postings.

 "We found that mycotoxins were present in >80% of hay samples fed to horses in the United Kingdom."

Now not all of them were the kind of mycotoxins that might be confused with ragwort poisoning on biopsy but we do know as I said above that this is assumed without biopsies.

"Interestingly, although not a specific finding, scattered individual hepatocyte necrosis and apoptosis are the most common histopathologic features in liver biopsy specimens collected from horses involved in outbreaks of liver disease in the United Kingdom." 

This is very significant because we can be sure what ever the cause that this shows that most cases are not ragwort poisoning, something which had been in print previously, but confirmed again here. 

Well, here is the conversation on Facebook. The quotes given are not the only source of information that I have to confirm this.  In case you're wondering my responses were in paragraphs. There is a way to do this on Facebook postings where normally pressing enter creates a posting, causing postings to be rather unclear.

Harriet Kate Fairhurst
Patrick Anthony Thirkell unfortunately, as an equine vet, I personally put to sleep 3 horses last year due to ragwort ingestion, causing irreversible damage to the liver. ingestion of ragwort causes Pyrrolizidine alkaloid toxicity, the alkaloids in toxic plants (such as ragwort) cause a primary toxic effect on liver parenchyma, leading to enlargement of liver cells, leading to impairment of cell division, resulting in large bits of the liver then being unable to function, ultimately leading to hepatic failure and death. There are many plants which cause it, however ragwort is the main perpetrator.

Bill Ellson
Harriet Kate Fairhurst How do you distinguish between liver failure caused by ragwort and liver failure caused by mycotoxins?

Harriet Kate Fairhurst
Bill Ellson ragwort poisoning specifically causes changes in liver cells termed megakaryocytes. On histology slides of a liver biopsy, these are very specific for ragwort poisoning.

Bill Ellson
Harriet Kate Fairhurst Really? Any peer reviewed science that supports that assertion

Neil Jones
Harriet Kate Fairhurst I honestly believe you are wrong.
First of all I think you'll find that megakaryocytes are bone cells responsible for
creating the platelets in blood.
I think you mean megalocytosis. Bill Ellson asked how you tell ragwort poisoning from poisoning by mycotoxins. Aflatoxins are mycotoxins and produce the same characteristic microscopic changes,
Indeed we know from the biochemistry why this happens and why they cannot be distinguished.
If more than one cause exists for an effect, then you cannot surely describe the effect as due to just one of those causes
A few excerpts from the literature:
"Hepatic megalocytosis can be observed in some aged animals, but is characteristic lesion observed in toxic insult by pyrrolizidine alkaloids and aflatoxins. " From Veterinary Toxicology Basic and Clinical Principles
"Hepatic megalocytosis is observed with certain toxic insults, particularly pyrrolizidine alkaloid toxicosis and aflatoxin toxicosis. " from Clinical Veterinary Toxicology.

 

 

 

Scientific Chinese Whispers over Ragwort

 All the time I see assumptions made about ragwort that my detailed study over the years shows to be wrong. People say things based on their prejudices that they assume to be true and I know they are not.

Frequently ragwort haters will say I lack authority in some way or other. You must go to peer reviewed papers, even when actually that research shows I am right. The authoritarian mind has been shown to be poor at thinking and there's good research behind that.  Thinking that authority is  the best source is also one of the biggest errors you can make in science. As  Nobel Prize winning physicist Professor Richard Feynman summed it all up in a famous quote made during one of his lectures, which was recorded on film for posterity.

"If it disagrees with experiment, it is wrong. In that simple statement is the key to science. It doesn't matter how beautiful the guess is. It doesn't matter how smart you are. Who made the guess . What his name is. If it disagrees with experiment, it is wrong. That is all there is to it."

He was talking about the derivation of knowledge about the laws of physics but the principle applies to all of science.  Experiment or evidence is the key not who said something or where it was written etc. I have here a classic example of why peer review does not necessarily assure validity.

Doing my research I came across a statement in a peer reviewed paper illustrating exactly why evidence is preferred over authority. It was saying something I had read a vet saying, that seedlings are eaten by animals and cause poisoning. Now I know, from detailed reading of the literature that small doses do not matter so this is not likely to be true and without evidence it shouldn't be accepted. There is even a published experiment where animals were fed lower doses of the type of toxins that are in ragwort and suffered no damage where as higher doses did cause damage. This is exactly what the biochemistry predicts.

As for challenging vets when I am not one. Again this is a matter of evidence not authority. I would guess that I know a lot more than the average vet does about this specialised subject area. I've seen what the textbooks do and don't say and as we know I regularly criticise a veterinary professor for talking nonsense, with really good evidence. I may have more to blog about this issue of vets getting things wrong in the near future.

Now what is a seedling? Well in my mind, as a native speaker of English, a seedling is something an inch or two high,  a new plant that has just begun growing from a seed. It is perhaps a lack of proper appreciation of that meaning that caused this particular myth to start. For as you'll see the origin of this myth has nothing to do with anything that could reasonably be called a seedling.

The first paper in the chain is this Epidemiology of intoxication of domestic animals by plants in Europe by Cristina Cortinovis, Francesca Caloni .which says:-

"Poisoning generally occurs when seedlings are grazed accidentally along with other forage or when there is a lack of other feed (Vandenbroucke et al., 2010)"

So the next thing is to follow that reference and it leads to Animal poisonings in Belgium: a review of the past decade by V. Vandenbroucke et al.

This says something rather different it talks about a lack of other feed, and isn't the primary source.

"Although herbivores seldom eat mature plants, poisoning can still occur when seedlings are grazed accidentally along with other forage or when there
is a lack of other feed (Polhmann et al., 2005)"

So this leads us on to what is the final source. It does not provide evidence just what is really the opinion of the author, but also a rather weird definition of seedling.

"Fortunately, herbivores seldom eat mature plants (Fig. 1), but poisoning can occur when seedlings (Fig. 2) are grazed accidentally along with other forage or when there is a lack of other feed." 

But just look at the pictures in the figures. They are below. These aren't seedlings but half-grown plants at the end of the first of their two years of life!  Through being repeated a false assumption has become stated as fact, as it appears a paper's author didn't check the primary source for validity. I have seen a video of a horse deliberately avoiding a plant like that.