I am breeding someone's bitch and she is on the 13th day of her cycle. I noticed she has a thick discharge today. It is white maybe slightly discolored. I have never noticed this on any of my bitches before. Is this normal?

My girls have a milky discharge when they are ovulating, but if I had a visiting bitch in, I would take her to the Vet for a smear. It could be anything with your description. The bitch owner will be happy to pay a vet bill if her bitch conceives. Call the bitch owner.