High Worm Count in 1 horse and zero in the other?!

[muffinthemule]

Please can anyone advise if they have any experience of this.....

I keep my two horses together on our own land with no others and get regular worm counts done. These repeatedly come back with very high counts for my 9 y.o. (Ca. 2,000 eggs seen!) and zero counts for my 18 y.o.

This seems very bizarre to me...can anyone advise if this is a common thing or should I be concerned about something more sinister in the high count boy?

NB - always worm this horse only and get a second count done which has always been zero...until they come back on the next count!

 

[cptrayes]

This is the whole point of worm egg counts, horses have an individual response to worms. Your older horse has an immune system that is highly developed to defend against worms. Your younger horse does not. He may develop better immunity as he gets older, or he may not.

It isn't, I think, widely understood that a horse with a really strong immune response will control a worm burden for itself. I used to think this only applied to bacteria and viruses, but apparently it is also true for worms.

 

[MochaDun]

I don't know if I've got this right but someone told me last year and it may be incorrect as I've just gone searching and can't find any hardened facts on it but it's only a certain percentage of horses on land are those with the biggest worm burden. Maybe it's just that one of your horses is one of those and your other horse isn't? Sorry to be so vague and unhelpful. Have you asked your vet about the results in case they can shed any light?

 

[soloequestrian]

It wouldn't be at all unusual to find horses on the same pasture with different egg counts, as the other poster's have said, because of the differing capabilities of their immune systems. However, 2000 epg is a fairly high count, and at 9 the horse should have a fully developed immune system.
Are the tests absolutely accurate? Would it be worth having them counted by someone else to make sure?
What are you worming with? I've seen cases where use of benzimidazole has actually increased the worm burden when it was measured again two weeks after worming.
Has the horse got any conditions that would interfere with it's immune response (eg Cushings)?
Do you use any form of control other than drugs (eg picking up droppings)?

 

[SpottedCat]

The other thing to be aware of, and the reason I don't worm count, is that it is well known that eggs will 'congregate' in the poo, so one bit may be really concentrated, another from the same sample may not. I don't mean the eggs move around (that would be insane), I mean that they will get laid in one bit and not another. There is quite a lot of evidence to back this up in the scientific literature, and this means that unless you take an entire poo, mix it up thoroughly in a bucket, preferably using a blender, then there will always be quite a high risk of false negatives - just selecting a sample from a pile of dung isn't sufficient to get an accurate count.

The reason worm count companies tell you the risk of false negatives is low, is because it is true for them! The risk of them not counting eggs in a specific sample is low, the risk of you picking a sample with no eggs rather than one with eggs is, however, much higher.

I think it is Ester on here who has more information about this, but i actually came across it through my vets when I was asking about worming a horse who had a digestive issue at the time - they advised against worm counting.

 

[Orangehorse]

I was discussing this with a livery yard owner, who does regular worm counts. The results of worm counts are very odd, with some horses you would think would have a high count don't and the other way round. They vary within groups kept together and even a pony kept by itself on limited pasture and droppings cleared had oneof the highest counts.

I don't have a clue what it means!

 

[soloequestrian]

but i actually came across it through my vets when I was asking about worming a horse who had a digestive issue at the time - they advised against worm counting.

So what did they advise instead?

 

[SpottedCat]

Either doing as I said - blending a whole poo together then taking a sample, if you really wanted to worm count, or using a standard chemical worming regime where you rotate the chemical used. I don't buy my wormer from the vets (never have), so they have no vested interest in me doing either worm counting or chemical regime. They were of the opinion that the risks from worm burden far outweighed the risks from using chemicals on a horse with a digestive disorder - and they were proven right, in that the chemical did not affect the horse adversely at all.

 

[ester]

Hi SC yes it was me, I would be doing my PhD in worms if I wasn't doing what I am! Worm eggs are known to be likely aggregated in faeces mostly just due to the worm's physiology (NB my history is mostly in sheep though ). My working is that for instance if we sampled 3g of sheep faeces this is proportionately much more of a sheeps poo than a horses and we could still get problems. To mitigate this effect the ideal would be to put the whole poo in a blender and take a sample from that. You have to remember that the lab are examining a small sample of poo. I don't think I ever found out how many grams they then use in their method (which will be mixed thoroughly) but I just struggle to see how this is representative.


they also do aggregate in the population so a small number of horses in a herd will have pretty much all of the burden, often youngsters (wouldnt say 9yo came into this category though!)

Horse have 2 ways of 'managing' worms resistance and resiliance. Resistance meaning that the horse will have a low FEC, resiliance meaning that they have a higher FEC but no associated symptoms or pathology.

OP what are you worming the 9yo with? I note that you do a second count (was going to suggest it otherwise!) showing that the wormer is effective but from that point of worming your horse is then being reinfected. From this I am guessing that you don't poo pick? It is helpful to know that due to the lifecycle of worms poo picking once a week in winter (twice a week in summer) is sufficient to break the cycle.

How often are you getting FEC done? just helps to build up a picture of what might be happening.

I always have to note on these threads that I am not against FEC, I am just not sure that the commercial method of doing things and the frequency that they suggest counting is sufficient. I am hoping to get hold of one of the spare microscopes here and a slide and I might then have a play in the garage though it has been a while. Wormer resistance is not an insignificant problem but they way FEC is marketed makes it seem the solution to everything and that it will give you all the answers

Ask away if you like and I will try and help if I can.

ETA SC got to the blender option first . I do think this affect can also be reduced if you FEC more frequently though, well it should help anyway

 

[muffinthemule]

Thank you so much everyone for your responses.

To answer the questions posed: horse is rising 9 y.o. 16hh eventer. I bought him at auction in Ireland so don't know his history but he looks well, is bright eyed and full of the joys at the moment (despite the high count). As I mentioned, he had a very high count mid-season last year and his performance/general demeanor did drop off until the worms were clear. He has no other conditions that I know of and is in regular work.

I wormed him then (August) with Equimax tablets which had the desired effect - zero worm count. Counted again at the start of October and negative...and now this!

My two live out 24hrs on 6 acres of good grazing and there has never been onother new horses near the grazing in 3 years. There are no other horses in the vicinity.

In summer the fields are poo picked regularly (probably 3x a week) however in winter we have been struggling with the fields being mostly under 2 feet of snow!

I guess this may be the problem?? However am still concerned that he is continuously reinfecting himself...perhaps there is no sense in me repeatedly getting counts done...perhaps my money is better spend routinely worming him every 3 months (which was in fact what I was trying to avoid!)

....or maybe i invest in a stable blender.....?!

Thanks again

 

[ester]

hmm ok I am thinking!

it is worth noting that there is no such thing as a count of 0, just <50 eggs per gram of faeces. Therefore the animal could be still reinfecting the ground after returning such a value. The same applies to your other horse really and that is where they question of whether those <50epg values have been accurate as this is the horse that hasn't been wormed and if that value was incorrect that horse could have been contributing signifcantly to the load on your paddock (which is a good size for 2 aswell).

I would suggest that the reinfection is unlikely to be due to the lack of poo picking in the snow but in my head it might work that the older horse does have a higher load and during the warmer weather before and after xmas the younger has had an increased load.

I think I can only suggest what I might do with mine!

I think I would want to try and start with a clean slate so to speak I would ensure that the field was poo cleared (no need for 'fresh' pasture.. that's another story!) and I would worm both horses. I would then reinstate FEC and monitor the younger horse in particular. It might be worth speaking to your vet to see if they have the facilities to do this, most do and it can work out cheaper.

 

[soloequestrian]

When was the sample for the last count taken? If it was after the very cold weather started, then it seems even more odd to have such a high count. You would expect any small redworm (which make up the majority of the worms in a count) to have encysted, and so not to see eggs in faeces. Likelihood of reinfection over such a cold winter is low - worm eggs are killed by low temperatures (and dessication). I think I would question the results - perhaps something got mixed up in the lab.

With regard to blind worming, I think recommendations for this are insane. Resistance is set to become a massive problem - all worms will be come resistant to all wormers with time, and worming prophylactically will only speed that up.

See http://solo-equestrian.blogspot.com/2008/07/worms-and-worming-new-thinking.html

 

[ester]

but it is an assortment of measures that will prevent this happening.

allowing a refugia and not expecting complete eradication of the population
not underdosing (a huge issue for resistance development)
appropriate wormer rotation (not every dosing)
appropriate paddock rotation (NOT moving after dosing)
appropriate treatment of new additions to the herd.


I am all for FEC as part of the system but it has inherrent inaccuracies and should not be soley relied upon to give an absolute result. It is just more complicated than 'here do these FECs and you might not need to use (nasty) chemical wormers that will solve the problem.

But we do have a huge problem that there are no new formulations in development and other countries (most notably mexico) have got triple resistant worms as we have in sheep

I do agree that the OPs situation for this time of year is unusual though I wouldnt want to come to any sweeping conclusions on it atm! I might well have a chat with my vet about it though and keep the situ under observation.

 

[SpottedCat]

With regard to blind worming, I think recommendations for this are insane. Resistance is set to become a massive problem - all worms will be come resistant to all wormers with time, and worming prophylactically will only speed that up.

See http://solo-equestrian.blogspot.com/2008/07/worms-and-worming-new-thinking.html

But the thing is, if I keep my horses on a poo-picked paddock (which I do) and there is very limited rotation in and out of the herd (there is - I have my two kept together), and I do not graze on other horse grazed pasture (I don't), and new horses are routinely wormed before being introduced (they are)...how will I be contributing to a resistance problem. For resistance to be a problem, not only do you have to have a horse which is infected in the first place, and it to develop resistant strains, you also require other horses to get infected with the resistant strains, which would mean rotation in and out of the grazing herd, surely?

I think that seeing FECs as a panacea is equally as dangerous, especially if you then move your horse about.

If people want to FEC then that is fine, but they need all the facts and to realise that there is a high chance of a false positive unless they are prepared to take a whole poo (and preferably more than one), put it through a blender and then take a sample from it. It really isn't the 'wonder alternative to chemical treatment which will prevent resistance, save you money and mean you don't put unnecessary chemicals into your horse' which the commercial companies would have you believe it is.

ETA: worming with chemicals without worm counting is no more 'doing it blind' than not worming because the FEC has come back clear, unless you are collecting poo, blending it and taking a sample from that as described above.

 

[soloequestrian]

But the thing is, if I keep my horses on a poo-picked paddock (which I do) and there is very limited rotation in and out of the herd (there is - I have my two kept together), and I do not graze on other horse grazed pasture (I don't), and new horses are routinely wormed before being introduced (they are)...how will I be contributing to a resistance problem. For resistance to be a problem, not only do you have to have a horse which is infected in the first place, and it to develop resistant strains, you also require other horses to get infected with the resistant strains, which would mean rotation in and out of the grazing herd, surely?

I think that seeing FECs as a panacea is equally as dangerous, especially if you then move your horse about.

If people want to FEC then that is fine, but they need all the facts and to realise that there is a high chance of a false positive unless they are prepared to take a whole poo (and preferably more than one), put it through a blender and then take a sample from it. It really isn't the 'wonder alternative to chemical treatment which will prevent resistance, save you money and mean you don't put unnecessary chemicals into your horse' which the commercial companies would have you believe it is.

ETA: worming with chemicals without worm counting is no more 'doing it blind' than not worming because the FEC has come back clear, unless you are collecting poo, blending it and taking a sample from that as described above.

If you have all these measures in place, why are you worming at all? If there are no worms present, then worming is obviously pointless. If there are worms present, and you are worming, you will be selecting for resistance alleles. There is no way round that. I understand that FEC isn't totally accurate, but as far as I'm aware it is the ONLY way to gauge worm burden (discounting tapeworm) and therefore vital in any programme of worm control. For me it is absolutely the alternative to routinely worming with chemicals - if your horse has a very high worm burden, it is very very unlikely that FEC won't pick it up. If the horse has a lower burden, then it's probably best left alone anyway. Although there is a 'standard' of worming at 200epg, there is no evidence that higher burdens are a problem for horses, however there are suggestions that a very low burden can have negative implications for the horses health. To be clear, I am talking about small redworm. As I understand it, large redworm is virtually non-existant in the UK horse population, and it was the real danger which lead to the type of blanket worming programme that is traditional in our horse industry.

 

[SpottedCat]

Because I haven't the faintest idea what is/isn't present on the grazing of the yard I moved to about 18 months ago. I don't have a blender to sacrifice to the cause, so I don't think FEC will give me as accurate a picture as I need to be satisfied that worming isn't required at all, and whilst I certainly don't worm as often as the drug companies would have you do, I do still worm. Whilst I don't turn out on other paddocks, except within the yard, I do allow a pick of grass at an event, so the potential for infection is there - but the problem of resistance is, I would say, very unlikely to come up in this case.

I think it is just as concerning that people use FEC without understanding the drawbacks as it is that people blanket worm unnecessarily. Chemicals are not all bad, and FEC are not all good, and vice versa.

 

[cptrayes]

perhaps my money is better spend routinely worming him every 3 months

What have you been worming with? Only a couple of the drugs on the market have a 13 week interval, most are 6-8. Perhaps this is part of the problem with this horse - maybe worming at longer than recommended intervals has allowed his worms to build up a resistance to the drugs? I'm no expert, perhaps one of the people who are can tell us???? I'm interested in the answer because I have to kind of "force" myself to worm my bouncy shiny horses at 8 weeks.

 

[Britestar]

I would add that your problems most likely arise from the fact that you have no idea of his previuos worming history. I had the same issues with my mare I bought from southern Ireland, and despite regular wormming from the time she came to me, I could never get her 'free' of worms so to speak.

Ultimately it caused her to suffer smalls bouts of colic at regular intervals (not that this had anything to do with her death)

 

[ester]

you are only selecting for resistance alleles if by random mutation they are there in the first place.

FEC is an excellent way to gauge worm burden but that doesn't mean I think it is being done properly.

CP the OP used equimax so ivermectin, 8 week recommended gap so it is possible that that has contributed to the problem.

Solo I worm 2 or 3 times a year given that I know the full history of my grazing and the frequency it is poo picked. 2 of those would happen whether I FEC'd or not. encysted in the winter months and a tapeworm dose in spring and or autumn.

I have in the past sometimes dosed with ivermectin mid summer but often don't and a low FEC score would not stop me from doing this as I wouldn't trust a one off result as they are much better used as a longitudinal guide to worm burden. When I had the ability to I was doing them monthly.

I shouldn't get involved in these posts

 

[FairyLights]

re resistance. I read in a vet book for horse owners recently that resistace happens thus ;
horse is wormed, most worms are destroyed but a few remain. those have an immunity to the drug as it didnt kill them. some weeks later horse wormed again with same chemical, some worms are destroyed but more remain, by the 4th worming with the same drug a fair number are immune. that is why it is necessary to chane chemical yearly. changing it at every worming is counter productive as it just causes blanket immunity to everything ,and just keeping on worming with the same chemical year in year out ditto. I have a closed herd and poo pick. i worm only on veterinary advice and the vets do the worm count ,I then used the advised drug. so far my weanlings,bought at auction in oct 2010 have only been wormed once,a double dose of strongid-p for tapeworm too, this was in Nov 2010. worm counts have come back very low or 0 since so no need to worm again yet.

 

[ester]

I should add that the largest selective pressure you could apply would be to worm your animals then turn out on totally clean pasture. IF any worms are resistant you will then have 100% of your worm population resistant to that chemical, that technique is still used frequently in the farming community but not recommended

 

[celfyddydau]

Very interesting discussion. I have counts done. There are 3 horses in the paddock which also has sheep from March until December.

I used to poo pick when it was just my horse and his friend but since the 3rd horse I stopped poo picking as it was getting silly, just me picking with 50 sheep and 3 horses made it a daily job that took an hour.

With the worm counts I pick a poo at random to take to the vets, last year there was 1 egg in the sample. My horse was on his own from 6yrs old until 16yrs old and his counts always came back as clear. The other horses were wormed until the owners decided that the counts being clear meant they didn't need to worm. So non have been wormed for 3 yrs.

Would the picking at random mean that I am getting a false negative or does having sheep in the pasture help to break up the cycle?

 

[Wagtail]

Please can anyone advise if they have any experience of this.....

I keep my two horses together on our own land with no others and get regular worm counts done. These repeatedly come back with very high counts for my 9 y.o. (Ca. 2,000 eggs seen!) and zero counts for my 18 y.o.

This seems very bizarre to me...can anyone advise if this is a common thing or should I be concerned about something more sinister in the high count boy?

NB - always worm this horse only and get a second count done which has always been zero...until they come back on the next count!

Do you take one to competitions or out riding with other horses? We have a small livery yard and usually the worm counts come back as low or zero. But last year one came back as high. He was the only one that had been out competing.

 

[soloequestrian]

My take on it all:
Large redworm can kill horses - they migrate into intestinal blood vessels, and if numbers are large enough, block them, kill bits of gut and cause catastrophic colic. During the 1960's, and onwards, blanket worming was recommended to control these, and it worked - large redworm is an uncommon parasite now.
The parasites we do have now are much less of a threat. Small redworm are the most numerous, and they would very rarely cause life-threatening conditions. In large numbers, they will cause ill-thrift, and if they all erupt from their encysted state at once they can cause inflammation of the gut, so they do need to be controlled, but not with the same sort of urgency as the large redworm.
We are living with the hangover of the need to control large redworm, which we don't really need to do at the moment. The drug companies want to sell product. Most people fear worms, and like to feel they are doing something definite in terms of treating their horse. All this leads to massive overuse of wormers, and the development of resistance.
We also tend to ignore the fact that most horses can deal with most worms themselves, with very little help from us other than good management (low stocking density, good health etc). I'm very suspicious about treating horses specifically for encysted redworm. If they have low FEC's, where would all the encysted larvae come from? It seems to me that around the time large redworm became less of an issue, a product was launched that could control encysted small redworm larvae, and so the problem was also 'launched' on an already fearful horse owning population. In addition to this, there is widespread resistance to benzimidazole now, and encysted larvae are just as resistant as adult worms, so the most commonly used treatment for encysted larvae probably doesn't work much of the time.
To me, resistance is a far more worrying problem. What we need to do is lay off the chemical wormers, and manage worms in a much more specific manner. To do this we HAVE to use FEC's (and preferably tapeworm antibody testing too). If usage of chemical wormers was to decrease so that they were only used when absolutely and utterly necessary, they would gradually become more effective again as resistance genes in the worm population became diluted.
See http://onlinelibrary.wiley.com/doi/10.1111/j.2042-3292.2010.00084.x/abstract

 

[MochaDun]

The other thing to be aware of, and the reason I don't worm count, is that it is well known that eggs will 'congregate' in the poo, so one bit may be really concentrated, another from the same sample may not. I don't mean the eggs move around (that would be insane), I mean that they will get laid in one bit and not another. There is quite a lot of evidence to back this up in the scientific literature, and this means that unless you take an entire poo, mix it up thoroughly in a bucket, preferably using a blender, then there will always be quite a high risk of false negatives - just selecting a sample from a pile of dung isn't sufficient to get an accurate count.

The reason worm count companies tell you the risk of false negatives is low, is because it is true for them! The risk of them not counting eggs in a specific sample is low, the risk of you picking a sample with no eggs rather than one with eggs is, however, much higher.

I think it is Ester on here who has more information about this, but i actually came across it through my vets when I was asking about worming a horse who had a digestive issue at the time - they advised against worm counting.

Thanks for posting this as it is always something I've wondered about since I've moved to worm counts.

 

[ester]

granted it would follow that if you have low FECs over the summer months you are unlikely to have a problem with encysted redworm. However I would only not treat for this if I could be really happy that the FECs were accurate. I wouldn't say that benzimidazole is the most common treatment used nowadays I would guess that moxidectin as a single treatment has surpassed that.

but yes I would agree we do have to use FECs but we have to use them, an I would say more importantly interpret their results accurately which I think is hard for the labs if they don't have full information on the horse's situation which would so much affect the interpretation.

The thought of triple resistance is pretty terrifying. thanks for the article solo I will have a look, will make a change from microbiology . I do also think much of the problem is owners also worming inappropriately as most seem to have little knowledge of what wormer they are using when and why

Note from eminent professor on site with me, if you buy a new horse worm count it. Treat with ivermectin and keep separated, worm count again and if the count is not <50epg get rid of said horse quick.

Sheep are the best hoovers for horse larvae so you are doing well there

 

[MochaDun]

you are only selecting for resistance alleles if by random mutation they are there in the first place.

FEC is an excellent way to gauge worm burden but that doesn't mean I think it is being done properly.

CP the OP used equimax so ivermectin, 8 week recommended gap so it is possible that that has contributed to the problem.

Solo I worm 2 or 3 times a year given that I know the full history of my grazing and the frequency it is poo picked. 2 of those would happen whether I FEC'd or not. encysted in the winter months and a tapeworm dose in spring and or autumn.

I have in the past sometimes dosed with ivermectin mid summer but often don't and a low FEC score would not stop me from doing this as I wouldn't trust a one off result as they are much better used as a longitudinal guide to worm burden. When I had the ability to I was doing them monthly.

I shouldn't get involved in these posts

No you should Ester! I struggle with some of the scientific detail about worming as it all seems so complicated now you are left as an owner barely knowing what is best to do/not do

 

[ester]

ah also wanted to add that encysted are more resistant but that is due to their encysted status not their genetics.

oh and I always feel a tad sorry for the worms in all this, they are only obeying the rules of evolution even it is somewhat unnatural selection

 

[ester]

trouble is MD I could be talking absolute rubbish. I know those involved where I am would much prefer us to all be FECing but I don't think owners know enough about it before deciding to do this or just leave it to the YO.

I do know with sheep that commercially I think (or it was) all done a bit differently so you weren't leaving some animals untreated but an sample from a number of sheep in the herd was taken and an average FEC produced on which a decision to treat/not to treat the whole herd could be made. Obviously this has lots of problems too.

The other option is to have a 'sacrificial' horse in each pasture which is never treated and maintains the variety in the population needed to help prevent resistance but I can't see many horsey peeps doing that!

In some ways I would love to see a situation developed where yards could do their own analysis, as most people could easily do it and could do it much more frequently than paying someone to do it which I think would be more beneficial, and it uses a greater amount of sample than other methods

http://www.innovis.org.uk/breedingproducts/horsesfecpak.asp

It is actually where I was kind of involved in the sheep side of things as we did use the FECPAK, this is the paper relating to the horses (one of the authors was who we did the sheep work for)
http://www.innovis.org.uk/Resources/The_Veterinary_Record_February_12_2005.pdf I hope people can see that link I'm logged into uni so can see it anyway

 

[muffinthemule]

Some very interesting posts here - thanks everyone. Not sure I have understood everything that has been said but very interesting indeed!

So...assuming my boy stays fit and healthy otherwise and the 10day post-worm count comes back <50 epg, would it be worth me doing further FECs at say, 4/6/8 week intervals? And then only worming if one comes back with a positive result?

And assuming I followed this route....am I best to rotate wormers or should I be following a specific plan?

Interesting point re: grazing at competitions which has made me think...I always let my 2 graze at events....wonder if this is a contributing factor..... *pondering....*