Probably not - as said it depends on the protien/sugar content. You can get high fibre haylage. It is more readily digestible than hay so horse will get more feed value out of it.
Depends which one you get - look on the horsehage website and they list all the different types and what horses they are suitable for.
I feed my boy Rye Grass in the winter and Timothy in the Summer.... if your horse is a good doer or you have lush grazing, I would stick to High Fibre or Timothy at this time of year as it has low sugar and starch content