Ask about medications first, which can be persistent in soils. Most bedding material is chosen to be safe for horses, wood shavings are very common, and compost beautifully with horse manure. they may also spray for flies, but that is unlikely to be a problem. If it's already composted, it should be dark and crumbly and relatively light, with a pleasant earthy smell, and you can plant in it right away. If it's fresh, it will smell like horse poop and will be heavy, with lots of "horse-apples", and will need further time either in your own compost pile, or dug in and allowed to decompose in the soil for several weeks. Anywhere in between you have to judge for yourself - my rough test is whether or not it still has "apples", and whether I would pick it up and smell it. Fresh manures can carry pathogens into the garden and onto your food, composted manures are far less likely to. Medications have a different effect, but they can accumulate i soils and crops, so it's wise to be aware of that potential.

You might want to pick up some HM for next year!
I will sometimes get a load, dump it in an unused area of the yard (I do have more than an acre),cover it, then leave it for a year and use some aged compost from the dump (very cheap at about $18 per truckload and certified organic)
I have gotten some from freecycle, and asked the lady if the horses were on meds, and if the HM was an organic product. She said it was OK. I went for it. You have to believe gardeners, I think! LOL Nancy

The stable where I get horse manure from uses sawdust and some straw for bedding in the stalls but nowhere near the 3 parts vegetative waste to manure manure ratio needed for composting. The manure they pile up usually justs rots away, loosing valuable nutrients to the atmosphere even thought they try to tell me it is "composted", because to many people simply piling up some organic matter is making a compost pile.
So after getting some of this manure (I try to get the latest, most up to datest stuff there) it is layered in my compost bins to properly compost and after that it is added to my planting beds. Now, I know these stabled horses are given worming meds as well as antibiotics one a regular basis, if the horses owners do not have a veterinarian visit regularly the stables owners will have one in.

ask:
What type of hay do you use? Do you feed weed free hay? (warning: persistent herbicides -- alfalfa hay in my area has less weeds than timothy hay, so I prefer that.)

What type of grain do you feed? (I've used HM from horses fed oats & beet pulp as well sunflower seeds. The sunflower sprouts now & then, but rarely an oat & no beets because it's pulp.)

Is the pile kept covered? (helps prevent leaching of nutrients)

If you can, I would ask who the supplier of the hay is so that you can ask the supplier if they use any sprays. If it is a legume hay (such as alfalfa), it would not be affected by clopyralid. Grass hays, maybe. I would also keep the manure in its own designated compost pile so that I could do a bioassay if I was in any way shape or form suspecting that there are herbicides.

I know a whole lot more about stable management than gardening, but I do compost my horses' manure and use it on my gardens. From the horsey point of view these are the things I can think of that may effect the compost--whether it matters or not may be better left to some of the more knowledgable folks here.

1. Don't assume you are getting stall leavings, which would be preferable. Many facilities "pick" their pastures and paddock of manure and the resulting piles would be comprised of almost entirely of manure with little to no vegetative matter.

2. Concentrate diet. I assume would be interesting as to what seeds would be passed in the manure. These days horses are getting a much more processed diet than the straight grain diets of the past. Yes, oats are still fed, but much more pelleted feeds. I know almost no one that feeds straight grains any more.

3. Forage diet. What type of hay is fed as most stall leavings will include some uneaten hay. I'm not so sure I'd be concerned too much about left over herbicides. Horse have extremely sensitive digestive systems (unlike cows!0 and I suspect any chemicals used in the haying process would have to allow for the horses to have ingested them without issues.

3. Medications. The foremost one in my mind would be what kind of worming program. Many facilities still worm on a 2-3 month rotation whether it is needed or not. The more up to date veterinarian suggestion is to do fecal exams first than worm as needed. Once I moved my horses to this type of program I cut my worming down from 4 times a year to once a year. Be aware that some facilities usually with a lot of horses coming and going will put all its horses on a feed through daily wormer. This might be the only medication issue that would give me pause.

Maybe I just don't get it, but I get about 50lbs of stall leavings a day per horse and use maybe 50-100cc of different injectable medicine per horse a year. That's about 4 oz. per 9 tons of stall leavings a year.

4. Bedding material. Straw, wood shavings, saw dust and wood pellets are the most common but bedding can be a local thing too--cocoa shells, peat moss, shredded paper all kinds of things could be used. Personally I think the wood pellets are the absolute best for composting.

5. Stalls flooring. This would be a question of is the floor impervious or not. An impervious floor--usually rubber mats or concrete--will include significantly more urine in the bedding than a floor of dirt or sand. Also ask if lime is used in the stall to control oder as I would think this could have an effect on the pH of the compost.

6. It would be nice to be assured that a facility has a system of dealing with "sharps." It seems like common sense but I've seen some places treat their muck buckets like trash cans...or worse...and finding a used needle in youR compost would make for a bad day. It would be worth it to get your compost from a place with good stable management practices for a variety of reasons!

I'm not sure how you can be sure, but it would be good to know if a stable's manure management lends itself to heated composting. I get a great mix of manure, pelleted bedding, hay and urine and it can't help but cook!

subk3 - that is exactly the kind of information that makes these forums valuable! I wonder about the use of anti-biotics though, is it as pervasive in the equine world as in meat production facilities?

At our 15 horse boarding facility we very rarely use antibiotics, less than once a year, and as subk3 noted we are talking about 3-4 oz. mixed into 10 tons........the oral paste wormers are used a few times a year but worrying about it is like not swimming in the ocean because somebody peed there last year.......I am growing 6,000 garlics in composted horse manure and the worm population is astounding and convinces me wormers are not an issue.

The ranchers I get my manure from, thinks that free means you move. Asking questions is not part of the deal.
One owner use no non-organic chemicals, so it is not an issue.
I agree with nancyjane, about stock piling for next year.
We had 27 horse at one time.

Herbicides definitely can be an issue with horse manure. From an NC State article:

"Aminopyralid, clopyralid, fluroxypry, picloram, and triclopyr are in a class of herbicides known as pyridine carboxylic acids. They are registered for application to pasture, grain crops, lawns, certain vegetables and fruits, and roadsides. They are used to control a wide variety of broadleaf weeds. If these herbicides are used on a pasture or hayfield, they apparently don't harm the animals grazing on the pasture or eating the hay. But some of these herbicides can be persistent and may remain active in the hay, straw, grass clippings, and manure, even after they are composted. Some of these herbicides have a half life of 300 days or more and aminopyralid has been reported to remain active in compost for several years. A problem sometimes arises when these materials, particularly manure and compost, are applied to fields and gardens to raise certain vegetables and flowers. The herbicides of greatest concern are picloram, clopyralid, and aminopyralid. The garden plants that are most sensitive to this class of herbicides are tomatoes, potatoes, lettuce, spinach, carrots, peas, beans, dahlias, and some roses."

tj

Here is a link that might be useful: The whole article

The use of antibiotics with most sport horses is not very common/excessive. At least with mine. I've had horses for 4 decades (most of that was as a one horse owner) and I remember using antibiotics maybe a half a dozen times if that many. What I've used the most of would be NASIDs (non-steroidal anti-inflammatory drug), mostly phenylbutazone (bute) or banamine. A typical dosage for a 1000lb horse would be 1-4 grams a day prescribed for inflammation. These are not terribly different from ibuprofen for humans. The other drug/supplement that is commonly used are glucosemine products, at most 5cc a week for a loading dose then 5cc once a month. But again we are talking about a gram or two a day in 50lbs of matter to be composted.

Parasites. Even with regular worming most horses carry a small amount of intestinal parasites. However, according to veterinarians most equine parasites won't survive a in a clump of manure on a day hotter than about 85 degrees. They are more resistant to cold weather.

I don't really know how to answer the herbicide in hay question. Most horse owners won't have any idea what was used for broad leaf weed control for their hay. I can say this: 2 4-D is the most commonly used broad leaf weed killer for agricultural in the world and I'm pretty sure it is not of the class that might be an issue. It is the herbicide I use when needed on my own pastures used for grazing and is the herbicide most people I personally know who grow hay use--including the source for my own hay. I've never run across anyone in my horse circle who has used their own composted manure/stall leavings and been anything other than thrilled with the results. So I would guess that the problem is on the untypical side of things and seeing my own results, worth the risk.

Having re-read the link article on the herbicides, apparently 2 4-D products are included. All I can say is that my four horses eat pasture that we've used 2 4-D on and the eat hay produced on pastures with 2 4 D usage and the resulting compost had an amazing effect on my plants. The tomatoes in particular took over the small kitchen garden and we've realized they need their own space in a new garden this year as we were afraid they would take over that half of the house and we might lose small children in the mass of plants. ;-)

bil lme, if you guys are happy to answer my less than brilliant gardening questions I am more than happy to add my stable management knowledge to the mix!

subk3, there are probably variables that play into it, but last year I talked to a friend with 2 horses, went over with my truck, and hauled away about 4-5 loads of well composted manure. It very negatively impacted my tomatoes and peas. The tomatoes that did grow were deformed. My options for rehabilitating these beds are to either purchase activated charcoal (which would be expensive) or allow time for it to naturally work itself out but that may take years. It was an absolutely heart-breaking experience. We are adding more compost and growing what we can in those beds but it could be a long road until this is resolved. We have talked to our neighbors who breed horses, they feed oat hay that is supposedly not sprayed. Before we use it though, we will be doing a bio-assay because the risk for us is not worth it.

When you say bio-assay, do you mean testing some of the manure on a small garden plot to see if it's alright to use before applying it elsewhere?

Basically, yes, except that it is being done in pots. There is a control group with sterile potting soil and then another group with potting soil mixed with the manure. Plant peas, wait and compare. There are better descriptions of how to do it online. I would not try it in the garden though because if it is not okay, you have a spot that is contaminated. The areas that I know are contaminated, I will plant a test in every season to see how things are progressing and if it is still an issue. It is basically my long-term science experiment.

I'm not sure about the activated charcoal remedy. Unless you have read studies where that worked, I would be skeptical, for the following reason: the sheer volume of *other stuff* in soil that can occupy the surface of the activated carbon, compared to the tiny amount of herbicide.

My solution would be more compost, in fact build a huge compost pile on the thing and get it really biologically active. Maybe a cover crop stage too. Hopefully it would not take years, but only another year or maybe two.