its all is going to be depend on the concentration of your straw and the motility
if you know if somebody that is already used semen out of the same collection
they might be able to give you a good idea of how the semen looked otherwise you should have a plan B in case the semen and doesn't look as good as you planned..
if you already have plan B in mind usually you will not need to use it, its when you don't you will get caught off guard
I would say if you have a straw that is packed as it should be and has good motility, you can about always split it 3 ways lap