They are territorial animals, not social. This means that they normally want their own place, not to share their lives with one another. Keep in mind, that when you let rabbits run together, they will fight. If you have one buck amongst a herd of does, you might as well consider that they will all get pregnant. The number of eggs that can be fertilized depends on the parents' ages.
Temperature extremes decreases the chances of conception.
At high temperatures, the buck stops producing viable sperm. When the buck is exposed to temperatures above 92 degrees, he may become temporarily sterile. It may take up to 4 weeks for him to recover. Extremely cold temperatures causes the doe not to conceive because her system is concerned with taking care of herself rather than nurturing young. The period between October and December is considered moulting season.