Another worming thought..

[The Moo]

We talk of worms becoming resistant to certain wormers but I'd like some clarification on this, I can see that if you use say... Eqvalan all the time for years then the worms in the pony and on the pasture can become resistant.

Is resistance built up any other way?

As has been mentioned, 5day Panacur is/was considered a bit feeble due to the worms resistance to it, but how can 'my' little redworms have become resistant to it when I haven't used that one for many years. My ponies don't share their pasture though I appreciate that they get the odd snack from the verge as we ride, so are unlikely (though not impossible) to ingest worms/eggs from horses that have 5day Panacur resistant worms.

When it mentions 'worms are becoming resistant' shouldn't that be 'worms are becoming resistant in horses where the same drug (not just brand) is used repeatedly'.

I am obviously over-thinking this and have a bizarre image of worms being like the Borg and part of the Collective where worms in Cornwall are becoming resistant to xyz so worms in John o Groats are as well

[zeldalithgow]

Hmmmm I do know that if you underdose with the wormer then the worms become resisitant - I try to over estimate the ponies weight

[harveydales]

Yes, underdosing can lead to resistance. I suppose if you underdose then there is a chance some of the "stronger and tougher" worms could survive and then these will reproduce, leading to a resistant strain. A bit like us not finnishing a course of anti-biotics etc. On the other hand, overdosing can cause problems in the horse so it's not easy. Also, as you say, if you worm your horses with the same wormer a lot, again resistance could build up. I can't see how else resistnace can build up.

I think the resistance they talk about is in certain areas of the country. I would have thought vets should know what wormers, if any, are not effective in their area but my recent experience has made me doubt vets are as aware as they should be.

[The Moo]

Ah yes, hadn't thought of the underdosing scenario but that does make sense, I tend to overdose if anything just to make sure.

But how do worms in a certain part of the country build up resistance when they are all (mostly) in individual ownership and have different worming routines, is it because of particular soil and grazing elements or maybe particular weather conditions or perhaps the marketing strategy of a particular wormer in that area making it the most popular.

Is it to do with cross contamination, horse A poops on the bridleway leaving Pancur resistant worms/eggs/larvae behind and then horse B from five miles down the road comes along and somehow picks them up to carry back to his/her pasture.

I can see that areas used for shows and events could be contaminated despite pleas from organisers for everybody to take their poo home and I can see that a big yard may have a problem due to its' worming management but a whole area?

Years ago I said to my vet that I poo-picked and worm counted as worm control he just said that was good but to still keep worming as per 'normal', I was disappointed with his reaction as I thought the idea of worm counting was so you didn't have to keep squirting drugs down your ponies neck.