I used to hunt a farm where the landowner had like 30-40 horses, they were a huge pain. Like everyone else said the deer were used to the horses and didnt mind them at all. The horses always seem to show up at the worst time and then wouldnt leave. Or you would be concentrating on the woods listening for deer movement and then you would hear nothing but the thunder of a ton of horses running by you. The deer were really smart too they knew we wouldnt shoot near the horses so they would run right out in the field and get in the middle of the horses and stay with them. I tried everything to keep them away, they would eventually after awhile get bored and leave but that was the only way, smaking them on the ass or yelling at them didnt do anything. Wow i just realized i still really hate those dang horses.