Suddenly aggressive pregnant English Buldog

Question
We currently have three dogs, 2 English bulldogs and our daughter's shi tzu that we have been caring for for over a year while she is in college. These dogs have always been together and we had no problems. We recently bred our bulldogs and now our female, who is pregnant, has suddenly become VERY mean and aggressive toward the shi tzu, starting fights, biting him, etc. Is this something that could be solely pregnancy related? I don't know what to do about this sudden change in her behavior. We have begun removing her from the roome, using time outs with her whenever she starts growling, etc., but as soon as we let her rejoin the other two dogs, it isn't long before she is back at fighting with the shi tzu. Any thoughts on what I can do???

Answer
Hi Linda

Once a female is bred, her behavior can change. A once docile female can turn into physco pooch.

The closer to whelp and after she may become even more aggressive.  Putting her in her crate giving her a stern "NO" and even keeping her on the leash in the house will help marginally.  Ensuring she doesn't step a paw out of line is what she needs.  

Good luck