If you do not have access to horseshoes, here is an alternative idea. Buy some big sponges and cut them into horseshoe shapes. Let the children sponge paint with the shapes. Take two latex gloves and fill with liquid tempera paint. Add enough water so the paint is evenly dispersed into the fingers.
Rubber band the top after filling, and place in container to take to the udder base frame.
The glove should dangle freely. Do the same with the other glove. Remove the rubber bands. Cover the floor with newspaper. Lay sheets of paper in the cardboard boxes.