depends on if its a wild one thats never been tamed or tamed and released one.
tamed and released ones will have lower barding diff as thier str and stuff that is used in the calculation will drop once tamed.
i believe that new untamed ones are like 110 and tamed and released ones are usually between 90 - 100
and you can gain effectivlly anywhere above and below your current skill within aprox 25 points of the critters barding difficulty.
so if you have a couple pretamed cu's that are all 95 in barding diff then you can start training on them at like 75 and you can go all the way to 120 with them.
granted, you of course will have slower gains at each end of the 20-25 point spectrum.