[Les Meehan]

I don't know about flash with horses but with dogs flash is no problem since their eyes don't react fast enough to see the flash (what they do react to is the high pitched whine as the flash recharges though).

It may be the same with horses, why not pop down to a stables and fire off a few shots with flash direct at the horses to see what happens. You may be lucky and it may solve your problem (and increase success rate on the day).

Let us know.

Les