I don't have any horses so I can't tell you about horse manure, but I would think you would really need some soil, perhaps from mole hills if you have any, mixed in to provide some foundation, otherwise it could all rot away to nothing. Some roots like carrots and parsnips don't like fresh manure but if yours is really well rotted then they won't object and your early crops will be magnificent! Veg such as squashes and tatties will adore pure manure though.
I grew up on heavy clay soil, so my suggestion is that you don't just plonk your beds directly onto a compacted area. You would need to do some work on the ground first. Break up the clay to at least one spit depth, and mix in a large volume of sharp gravel or hardcore for drainage, also allowing an escape drain for water. Otherwise your beds might as well be sitting on concrete. It's amazing how quickly a lorry load of gravel can disappear! Many plants need more than the depth of soil provided by a raised bed, so they will normally root down into the native soil, but if it's hard clay they may not be able to do so.
Watch out for slugs from your logs too.