Now Dave, I'm jealous. Not about the horse farm, horses are like dairy cows ... too much work, but in my opinion horse manure makes the very best compost for the garden. Strangely enough, living in East Texas, surrounded by horse places and horse lovers, I can't get my hands on any of the stuff.
When we lived in the country outside London, we had a stable about 10 minutes away. They would give you the manure and straw just to get rid of it. I hauled dozens upon dozens upon dozens of trash sacks of that stuff back to the house. I never kept it for 5 years but after two that stuff would grow rhubarb five feet tall. I had a little veggie garden but it kept the two of us fed the whole year and I had the best looking rose garden in the village.