It may be fully composted. The way to tell is to scoop up a big ol' double handful and plunge your nose into it. If it smells fresh like a forest floor after a summer rain, then it is finished composting. If it smells maneuery, dank, rank, moldy, yeasty, off, or otherwise not like sweet soil, then all it needs is a little more time to finish. Finished compost smells great.

You want to wait for it to finish composting or you risk the wrath of your family and neighbors. There is nothing more embarrassing than a stinky lawn. And the stink seems to last for months even though it only lasts a few days.

Almost everyone will tell you that you cannot apply too much compost. I will tell you that you can go broke with that philosophy. If you can get it for free, then go for it. The application rate for lawns is 1 cubic yard per 1,000 square feet. For garden beds you can apply as much as you can haul.

When I get horse manure I do it like this. I take one 5-gallon bucket and a new roll of 9-gallon trash bags. I put one or two bags into the bucket like a liner. Then I fill the bags 1/3 full and tie it off. Then I reline the bucket. If you put more than 1/3 full in the bags, you risk breaking the bags. The reason I do it like that is I don't have an open bed truck. I have to carry the compost home in a car or van. I can get a LOT of bags in a car like that. The best way is to borrow a truck and just shovel all you can into the bed.

skoot cat, it is likely to be fresh horse manure mingled with whatever 'bedding material' the stable uses (wood shavings?). You can use it in a compost pile or apply it VERY thinly on the lawn. Either way, invest in some industrial strength deodoriser to mask any undesirable odor.

skootcat, ......and this just in! In the St. Pete Times newspaper (01/12/2008), John A Starnes Jr. writes "...I feed my soil four times a year, in March, July, September and December, using a rotation of menhaden fish meal, fresh horse manure, dry dog food nuggets and composted mulch......."
Disclaimer. "This is not an endorsement for any product...etc. etc".

Thanks guys,

Im going to go check it out today after work. If I smell bad, Ill add it to my compost pile and let it finish.

Anything else I should know?

One other thought, besides the smell the reason most recommend against adding manure compost that is not well cured is because it can burn a yard. But, horse manure is not much of a threat on that issue. Many other manures will burn if too fresh, but not horse generally.

So, free? Go for it.

You want to make sure that it is finished compost. You have to think of what those horses have been eating. That would be just about whatever they can get their teeth in. For this reason the compost needs to be finished otherwise you risk getting the seeds from any weeds they might have been munching on. The other wood chips and stuff mixed in with it will actually be beneficial to you in that it is a wider diversity of food for the microorganisms in the compost. Just remember when composting to keep it turned, the microorganisms need air to live, the more air the more organisms the faster they will decompose the material. You should probably turn it about once a day or every other day.

Good luck, the compost should do wanders for your lawn/landscape