Some dogs just hit the ground running on any piece of equipment, others have to be taught/conditioned to that piece and still others just will not do squat. Allowing them to become familiar at a very young age is always the best medicine. For a dog that has never seen a mill and then tossed up on one at two years old can be quite the obstacle to overcome. Making things familiar to them is a must as they transition into 'working' dogs.

Some dogs who have been on a chain their entire life find it difficult to cross over the threshold of a doorway, never mind a cramped contraption that is constantly trying to roll out from under them making all kinds of different sounds.

I am not sure it is a fact that chain dogs do better on a jenny than a house dog or a kenneled dog. I put more stock in familiarity and exposure to different things when they are young. EWO