Announcements of free horse manure occasionally pop up on Craigslist.

Google "horse boarding" with your city state in the search phrase. They invariably are quite happy to get rid of some at no cost. You will be able to choose sites with easy access in and out and the quality of the product.

You may want to ask if the manure is aged, age it yourself or do the bean test due to the possibility that the horse may have eaten herbicide treated food.

I was planning on doing the bean test. I hear someone on line talk about it. I was thinking of keeping the manure as isolated compost over the fall. then testing with a bean

There are 3 ages of horse manure. Brown is fresh, Grey is composting. Black has composted or aged like a fine wine.

There are multiple choices to make based on the bedding in the stalls. With wood chips is the lowest grade. Manure with straw is hard to dig but if you're using it in a hot frame this will give you the most heat. Barns with dirt floors don't use bedding, so no straw, wood chips or sawdust, hulls or what not.

Black horse manure will be well aged when you get it and from my experience is ready to use. If the barn is placed on a hill side to access both levels with wheeled vehicles then the manure will be piled near it and dumped from the upper level, the oldest will be at the bottom of the pile. If the ground is level the pile will be big in diameter and the old manure will require searching around to find.

In my case the site that's the easiest to access uses wood chips, so I pass on that and go for the site that I have to use a wheel barrow to load a truck. I've found that to load a pickup truck with a wheel barrow is almost impossible for me. Easier is a truck and trailer rental. Or a small moving van with the included ramp. Hose it down well and drive it back with the door open!