I start by whistling for them every time I feed, once they start coming to that start whistling when I want to groom them, gradually work it up and they will start coming when you call. Kind of like training a dog to come. Start with treats/fun stuff (in theory they should like you
) and work it up to everything else. Flame (my old mare) will usually come when I call her name. Sometimes she just can't be bothered though, but she's an old girl so it doesn't bother me. They both nicker everytime they see me coming though.