Male Dog Response to dog in season

Question
OUr 4 yoa lab was acting excited the other day and I let him out and he threw his nose up in the air and took off. I suspect that a female in heat was in the area. What is the range of the smell, and how long will he stay with her?

Answer
Miles.  Who knows?  The scent spreads over a week before she is ready to mate.  He may need to stick around a week.  He could also be killed by a larger dog.  Traffic is a big hazard to a preoccupied dog.  Do him, yourself, and those foolish to keep unspayed females a favor and have him neutered if and when he gets back.  It also protects him from cancers later in life.