tied during pregnancy

Question
I found my dogs tied twice since we found out that the female was pregnant. She is already around 50days, and yet if I don't keep an eye on them, the male will start mounting her.  Is this normal?  and will it harm either dogs, or the pregnancy?

Answer
Hi Izumi

You do not want your male mounting your female after she's been confirmed pregnant.  You need to keep them seperate, he can induce labor and cause you to lose your entire litter.

It's not normal for a male to want to continue to breed after a female has come out of heat.