There aren't at this point. That isn't really something I'm interested in as I feel the prevalence of beastkin/halfkins fills that fetish fairly well. Considering the animals don't persist after the scene and are just there as a temporary "here, have another penis" method, I'm not sure what the benefit would be. I could see it more if the animals were persistent, trainable, had traits, etc...but then that's a whoooole new system.