This is my first year breeding, but as far as culling, I would only cull an animal if the animal could not live a healthy, normal, life. Other then that, I would not cull. As a breeder, I have the responsibility of each and every animal I help bring into this world and just because it isn't the color I wanted, or the sex I wanted, doesn't mean I should just get rid of it because it serves no purpose to me. If it is not what I wanted, and no one will buy it, then I need to make sure I have space in my rack and enough time and feeders to raise it.
I also don't believe in culling dogs. I bet there are plenty of people out there who want a purebred dog but can't hand over $2000 for one, so why not sell the "less desirable" ones for less instead of killing them?