I have in the past created beautiful aged manure for my garden … but in the past six months, I have a horse on thyro-L, prascend and now Steglatro. I have been taking all manure since then to the dump with the thought that some of these are passing through into the manure and would then end up in my garden. Does anyone know how long they ‘stay’ in manure? Probably not the right question, but ultimately I’m trying to understand if the manure produced could be used in the pile and then in my garden without consequence.
Interesting question. Let’s take a look.
Levothyroxine is converted to T3 by the body, and excess is excreted mainly by the kidneys (as pee) with approx 20% being excreted in manure. It’s pretty dang bio available (90+%) although high dietary fiber and consuming with a meal drops that. So, there is very, very little of what you feed the horse that’s being excreted in the poop. Levothyroxine is also “highly sensitive” to light and moisture, so the small amount that does make it through probably degrades pretty quickly.
Sources:
https://www.ncbi.nlm.nih.gov/books/NBK539808/
https://aapsopen.springeropen.com/articles/10.1186/s41120-022-00062-5
Pergolide is excreted by the kidneys. It’s also just not very stable at all, which is why Prascend comes in those little blister packs.
Source:
https://www.ncbi.nlm.nih.gov/books/NBK548593/
Ertugliflozin is excreted by both the kidneys and via manure, split about half and half, and about a third of the dose winds up in the poop. Ertugliflozin looks to be pretty stable, although it does break down with certain processes. It looks acid and oxidative hydrolysis do take place in a compost pile, which would breakdown this one.
Sources:
https://pmc.ncbi.nlm.nih.gov/articles/PMC7403171/
https://pmc.ncbi.nlm.nih.gov/articles/PMC10257675/
So, it looks like light, moisture, and composing will degrade anything that makes it through the horse. Let your poop compost, and it should be fine to use on your garden.
13 Likes
I’m so glad you responded - this is so helpful! Thank you.
1 Like
Your big problem will be the hay that you feed. Make sure it is not treated with an aminopyralid pass through herbicide like Grazon. But you may already be aware of this.
5 Likes
Will the ivermectin used in wormers pass thru and break down? Long ago I was told it would not and to be careful with my Aussies around manure.
1 Like
In short, yes, absolutely, ivermectin (and moxidectin, and all the dewormers) do break down in manure.
Here’s a layman’s summary of one study done on the half life of iver/moxidectin in manure and its breakdown, with more info on when it’s safe for a sensitive dog to eat.
What breaks down and how quickly is going to hugely depend on how hot the manure pile gets.
And as noted, Grazon and the like can devastate your garden. We can’t give horse manure away anymore as so many gardeners have been burned by this issue.
1 Like
Very informative. Thank you.
1 Like
Oh I never thought about that … I’m checking with my hay people now but I have used the aged manure in the past in my garden, and it’s never had a negative reaction.
It’s illegal to let hay off any property where the field was sprayed with aminopyralid (Grazon and all its variations like Grazon Next) without making it clear it was used and what it means. It’s not as widely used as some make it out to be, but it IS used, so if in doubt, just ask.
I will also chime in on the Grazon/aminopyralid issue. One year I got gorgeous hay from a new supplier, my aged manure always goes onto my vegetable garden, nothing else from an outside source is put on it. It was three years before my vegetable garden recovered. Thank God I didn’t give any to the flower farm across the street that specializes in dahlias since it is absolutely lethal to them, and dahlias aren’t exactly something you can just restart from seed.
Ironically, I now look for hay that has weeds or clover in it. The dealer had said that hay wasn’t sprayed with an herbicide…but it most assuredly had been, as tests ended up showing. I later found out that the hay had passed through at least two dealers on its way to me. It was a bad hay year so people were scrambling.
If I ever get hay from a new supplier, I will definitely run a seed germination test first on several bales before using the compost on the garden.
3 Likes
That’s just… 
Yeah. No-one is going to prison for this so hay brokers don’t care. I know literally dozens of gardeners who have been burned and have even had it pop up in mulch on commercially seeded sites. It’s not worth the risk for people with carefully tended gardens of perennials or people who grow vegetables.
2 Likes
Yes I know but growers don’t read the label or they just don’t care. My Grazon disaster was from hay purchased from the feed store, that the feed store grew. I had used manure in the past with no problem. However one year I had several plants that I thought had Curly Top virus - knowing what I know now, it was probably Grazon. So after the county agent educated me about why all my plants had deformed and were dying, I went back to ask the feed store what broad leaf herbicide they used on the hay. “Oh we don’t use a broad leaf herbicide”. Finally they admitted that they had used Grazon. I don’t buy hay from them anymore.
But I do buy from resellers and they have no idea what was sprayed on the hay. So to be safe I make a compost pile in the pasture for each batch of hay I feed. If it grows weeds it is safe. And an even better test is to put some of my bad tomatoes on the pile and if I get healthy volunteer tomato plants I know I am safe. No more will I add stall cleanings without composting it first and testing. When I buy from the grower I ask what herbicides they have used and the people that have good hay will be upfront with me. If it is good hay I will buy it but not use it in my garden. This would not be a problem if people would not use it non-label and be transparent.
3 Likes
Well, this is certainly apropos for me. I was having lunch today with a horsey friend whose Mare is actually in the early stages of a laminitic episode right now and we were talking about medications and grass and so forth. She told me that when her one Mare is on antibiotics, anywhere where she pees that kills the grass. And then she told me that her other horse everywhere she pees grows back bright green. I’ve seen the bright green with dog urine, but I’ve never noticed it with horse urine. And the antibiotic thing is certainly odd. Has anyone else ever heard of that?
I have never seen the bright green with horse urine or dog urine.
horse urine is usually alkaline, dog urine is usually acidic
Yeah, I thought her whole description of the results of her horses pee was very odd. I’ve never heard of anything. She was adamant about it.
