It has been more difficult to start pups that have been in small pens sight chasing domesticated rabbits. They tend to use their eyes and heads up rather than nose and tracking. They will jump a wild rabbit but, wild rabbits are not going to just stay within nipping distance of them, so they have to start tracking. Once the rabbit is out of sight then they lose interest are start to look for another. IMO it's great to introduce them to rabbits using domesticated rabbits at a young age, but the older they get, I have seen it make starting them on Wild rabbits more challenging.