Put a calf in a pen by itself. Leave Mama in another pen. Then, take him and make him 'drive' the calf and do nothing but move toward it. Keep the calf in front of him and show him that he can drive it and control it.
When that calf stops moving, go get another one and drive it.
When I used to get in horses that were terrified of cattle, I took them to the local sale barn and drove cattle off of the scale to the buyer pens. About 6 hours of doing this at a big sale and the ears went back they wanted to drive the cattle.
I had a really nice cowhorse one time that started out great. At about our 5th or 6th show (we were leading the State Association in 'Working Cowhorse' at the time) they had a set of Holstein yearling steers (horrible cattle to work) and he had never seen a 'paint' cow. He trembled and shook and squated down while boxing it. People thought he was being a 'great' cutting horse and all he wanted to do was turn tail and run away. Going down the fence, he tried to turn it from 15 feet away (the closest I could get him to it). Everyone that had been clapping was laughing by then! When we circled the steer, he looked like the Indians circling the wagon-train. I could not melt and pour him on a paint cow at that point.
I finally bought 4 Holstein steers from a dairy and drove and drove and drove them and he finally got over it.