if the ivory is been properly aged since its been harvested over 10 years and it is properly cut there is zero risk of brekig with it, if its "green" ivory from a small diameter tusk like those from Taninzia(SP?) then there is a significant risk of it cracking, additionally, the ferrels are ivory alot of times on shafts which is much thinner and you can dig down deep and fire balls in with them and there is no problem.
in summery its the care, cut, and knowlege of the cue maker that will insurrance the quality of a ferrel to make it suitable about ivory,
not to blow my own horn-yes I know I'm guilty of that sometimes, but of any topic here on AZ I know more about ivory than any other, Its awaly facinated me since I was a kid.
also yes bulls breaktheir tusks fighting, its an amazing sound to hear in real life 50 meters away in a forrest, they also use them to move trees push them down and break them doing that as well, one final point elephants are right or left handed like we are, so they have one tusk the working tusk, that is more wore down, thicker and more dense than the other side, thats the side you want for balls, butt plates, joints, and ferrels since its the most dense, the other side is good for inlays and points.
ivory class is over almost....thereare more elephants in Africa today than ever since game counting started over 100 years ago, some areas like Serria Leone they are endangered and harvesting them from there is bad, they are poached to feed people not for the ivory trade, i could keep going on but I wont, I go to africe 2 times a year until my back went bad and learned alot, i talk to my friends there weekly. so this isnt BS.