I have the person I get manure from to tell me when they worm horses.. they do it twice a year. I have read not to use manure from wormed horse for 7 days after worming so I don't use the manure coming from the horses for 8 days just to be safe. I put it straight into my garden and want to protect my worms. I would guess that composting would break it down and dilute it but have never seen any posts regarding this. If I thought the manure was possibly unsafe to use I would compost it by itself and then put a couple worms in some of it and see how they do before using it.

Thanks for that info, I was thinking of doing a series of test with some worms in the manure for 1 week, 2 weeks, 3 weeks and further to determine for my self, what is a safe time frame for the break down of the medication.
I was actually hoping someone on the forum my know this answer to save me the job.

Steve.

A study of manure to see how long the adverse affects of worming medication lasted would be beneficial. I can find studies that show that worming medication will kill off red worms if the manure is composted shortly after dosing, but have seen nothing that shows the time frame before the manure is good to use again.

Here is a link that might be useful: Worming medication affect on compost

Well that is a new one I had not considered. I wondered if it would even affect earthworms, being different species and all.

lolol...use the manure the ppm that might have made it past the horses liver is neglagable. talk about beeing hyper sensitive scatter the manure around and till it in and by the time that all the sun,rain and irrigation has run through it there wont a problem ppb (billion) if any of it is left.....does anyone breath rush hour air in the downtown core?or are we like the Japs and walk around with Micheal Jackson towels on our face?

Thanks kimmsr, that science project link on worming medication and red worms was exactly what I was looking for.

Horse wormers degrade rapidly. Ivermectin is a very common wormer for horses. The following quotes are from the link below.

"As abamectin and ivermectin undergo rapid degradation in light and soil, and bind tightly to soil and sediment, they will not accumulate and will not undergo translocation in the environment, minimizing any environmental impact on non-target organisms resulting from their use."

"They display little toxicity to earthworms (LC50 values of 315 ppm and 28 ppm in soil for ivermectin and abamectin, respectively)"

I would also add that while there are some farms that use a daily worming feed supplement that method is no longer recommended because of the development of resistances. Most facilities will worm 3 to 4 times a years. Some farms like mine worm according to fecal test, for me that means most horses here are wormed once annually.

Here is a link that might be useful: PubMed on Ivermectin in the environment

https://www.collielife.com/Health/dangersofhorsemanure.html

If it can do this to a dog what can it do to an earthworm!