I have horses as well and the advice here is spot on. Verbalize so the horses recognize you as human, slow down or even stop until you see how the horse is going to react. My young horse Tat has seen plenty of bicycles and I have even "trail ridden" with my husband on his mountain bike. But a bike coming toward him quickly on the rail trail would most likely scare the crap out of him. It's on my to-do list to get him to the rail trail. Most horses on the rail trail are fine because they are used to bikes, but I guarantee the first time I take him will be very exciting and I hope that the bike riders don't make the assumption that he is used to bikes. With horses the first time doing anything new has the potential to be exciting!
Rita Marie
"No hour of life is wasted that is spent in the saddle" -Winston Churchill