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Horse deworming meds vs. composting worms

This topic was discussed in an earlier thread, but I'm not sure where. I don't have horses, but I know a number of you might be interested in this info. It's from

Will horse dewormers kill red worms?
The most common wormer used is known by the brand name Ivermectin® made by the Merial
Company. Merial’s research shows that the active chemicals in Ivermectin® are deactivated when
manure is exposed to sunlight. Equine studies show that 95 percent of the active chemicals in
Ivermectin® are deactivated in the horse before being passed in the feces. Leading experts in
vermicomposting believe that the concentration of Ivermectin® in the horse manure is not high
enough to seriously injure Eisenia.

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Hi Susan,
It would be nice to finally put this matter to rest. We had planned on doing an experiment about this very subject with some of our worms in a controlled environment, but unfortunately, we were on vacation when the horses that we get our manure from got dewormed. Now it is too late and it won't happen again for a few months. We will definitely do it then and report back.

I also recall reading that dewormers used for most livestock target intestinal worms at specific stages of development, thus they need to be administered the dewormers at specific durations to be effective. Because of this I think that use of the manure may not be harmful for EF worms, though I'd feel more comfortable using it if someone out there has used horse manure knowing the animal(s) were treated and had no problems.
The web site I cited is a horse farm that does vermicomposting on the side to take care of the large amounts of horse manure. I'm sure they've tried it and would have mentioned ill effects. I'll be interested in hearing what Beth and Dave have to say in a couple of months.
Hi Susan,
I apologize for not doing this experiment earlier. Our timing with the horse stable didn't work out until recently. We started feeding a small bin of red worms with the "tainted" manure in early May. The manure is from horses that were given Ivermectin. So far, the red worms seem to be fine...actually very healthy. I put on a couple of blog posts that you might be interested in. I will be posting updates every few weeks or as time permits. Since the bin is small, it will be very easy to monitor. We received an interesting comment..."Could the medication make the worms sterile?" Only time will tell. I'll report on that too.


was this experiment followed through with or did it just fade away?

I still would not feed my worms anything that I would not eat.

ughhh, you must eat some interesting things LOL

I've wormed my horse a couple of times in the past 9 months I've been vermicomposting.   I vermicompost 44kg manure/day.  With such a huge amount of manure, it might have diluted the effects some, but I started in Feb 2011 with one kg worms and now have around 80kg.   So..... it doesn't seem to have affected me seriously.    So far.....

What do you use?

synelg, how did you figure out the weight of your worms? Even just in my RM bins, my estimate is ALWAYS off. How I know this? Because I did the dump and sort afterwards and it's always been less than my estimate.

""44kg manure/day"" From how many horses? What did you do with the manure before you were VC-ing?

Wish I have easy access to horse manure.


Hi Sue

I estimate the kg by how much manure they're using.   I usually collect from 2 horses, although there are several more I can collect from.   However, 2 horses produce around 44kg of manure/day.   I know from my home bins that they go through maybe a half of their body weight/day of manure, so if they are going through 44kg/day at the paddock, then I assume I've got around 88kg of worms, and increasing exponentially every day!  

Before I VC'd, the manure just got harrowed into the paddocks.

"they go through maybe a half of their body weight/day of manure" Finally someone whose worms do that. That's really amazing how they get to 88kg. in 9 months. Congratulations.

Never knew that horses make so much manure. The lady I picked up manure from at one time, cleaned up after 2 horses since they're in a residential area. No wonder she's so slim, lol.





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