Whereabouts in Newmarket is this said to be a problem?
The horses in Newmarket are only out when going to and from the gallops a couple of times a day.That means they'll cross the Bury Road, where it's leaving the town,or Hamilton Road by the Rowley Mile Course, briefly and escorted, doesn't it? Much of the route is on designated bridleways uniquely for the horses, not people.These routes are fenced off.
They're not walking down the High Street or in the streets themselves are they?
Anyway, console yourself with the thought that some, if not all of the horses are earning more than the rest of us, certainly a lot more for the town!