Hi Hugh,
Well rotted manure, i.e., 2 years old, whether from cattle or horses is compost. This point does seem to cause a little confusion for people but manure is manure while it is decomposing and when completely decomposed it is compost.
Different people have different ideas on what constitutes well rotted but how I judge it is, there should be little or no evidence of bedding, i.e., straw.
I also get mine in about 6 months before I plan to use it so I can be reasonably confident its is sufficiently aged and I also turn it occasionally.
Don.