question on vitamin supplements

[Susith@aol.com]

This is a question for Susan Garlinghouse or others who may have studied 
vitamin/mineral requirements in horses.

I would like to know if the contents of the Complete Feed such as Ranchway's 
All American, Purina, etc. are sufficient for a performance horse, or do they 
need all the extras that are available in the supplements such as Accel?

Over the winter while the horses haven't been working, I substituted the 
complete feed as their supplement and now that we're going back to work, I 
wonder if we need the "designer" vitamins or can manage on the Complete?

Basic diet is 60% grass hay, 40% alfalfa, 1-2 lbs grain.

Thanks,
Susan