how many ties to ensure pregnancy?

Question
My female lab won't let the stud dog mount and tie again. She is still in her fertile stage. She is very aggressive to him and sits down immediately and bites and growls at him. Can she become pg with only one tie?

Answer
A dog can become pregnant with only one tie. Most breeders prefer two, but one is plenty enough if timed right. If she's sitting down and becoming aggressive, then her time has came and went. But yes, most definitely a dog can become pregnant with only one tie.