These mistresses wanted to have fun with pony play and that is what they did. They did not want it to be the usual pony play. They wanted to ensure that they did what they had to and had a great time while at it. The mistresses also felt that they needed to facesit this loser and that is exactly what happened. He was double humiliated and it was not fun for him but for them it was.
These mistresses had beef with this slave and they had to torture him so that they would keep him from doing the things that they did not want him to do. He had been warned but he did not listen. So the mistresses had no choice but to use pony play training on him. In addition to him being a human pony, he was also slapped by the mistresses painfully.