From fhotd member hecate
http://fhotd64476.yuku.com/topic/4028
If your horses pick up ticks in the spring, Frontline them. One largest-size-dog dose of Frontline can be dotted along the roots of the mane, the dock of the tail, and around the fetlocks/pasterns. Just like with dogs, the ticks will still get on, but will die off fairly quickly. Some of my guys have very sensitive skin, but nobody's had any bad reactions.