Ratter, you should have seen the look on the wolfhound pup's face when he first set eyes on a horse in the paddock . He stopped dead in his tracks and stared. You could see him thinking "Blimey! My dad is a big dog, but that dog is bigger than him !" They're no trouble with horses; I suppose they think they're too big to bring down and eat. They ignore all small prey; rats, squirrels and so on; presumably on the grounds that these are too small to bother with, but hares and muntjac are another matter.
But I had a standard poodle bitch whose great delight was to go up to the horses and try to get them to move. If they did, she'd try to get them to trot, then canter...she was only happy if she got them to full gallop, even for a second or two, then she'd stop, object achieved. Trouble was they got wise to this game and just stared back at her, unmoving, or raised a warning hoof. Outwitted by a horse; what an insult!