Is she pregnant???

Question
Hi i have a female staffy named ruby that we have had for 6 years and we have just got a male staffy named dex who is 2 years and he is constantly trying to hump her and she is very aggressive towards him but if he isn't trying to hump her they are fine together do you think that she may be pregnant and this is why she is aggressive also how can you tell if she is pregnant i am not sure of when she was on heat last and she is a tubby dog so it is difficult to tell if she has put weight on but her back boobs seem to be bigger.

Answer
She has to be in heat to be bred. That's a given.  If she's wasn't/not in heat and your male is humping, that's just a dominance issues and one that you need to correct before you have other issues.

It's important that a female be in top physical and mental health prior to breeding.  So if she was over-weight you may have complications in whelp.

All you can do is calculate the time when a breeding would have occurred and add 2 months.  Or, the alternative would be to take her in for x-rays.

Good luck.