does sizes of the two dogs mating matter?

Question
Yes, we have a 5yr old male Bouvier and a 1 1/2 - 2 yr old dog thats what the people we got her from a few months ago said she was fixed but she went into heat shortly after we got her she is a shepard/lab they said she looks more shepard but she's pregnant about a month now. will she be able to birth those pups or will they be to big.

Answer
Hi Melissa:

It's possible her body will adjust the size of the pups but in any whelping, even those including dogs of comparable size, there's ALWAYS a potential for puppies larger than can be delivered vaginally. Obviously a size difference such as yours increases the possibility of whelping complications considerably.

I would advise having a simple X-ray taken when she's 50+ days gestation. This will not only give you a good idea of how many pups to expect but your vet should be able to judge whether or not they appear too large at that point. Unfortunately it's impossible to predict the outcome with a 100% degree of certainty.

I hope things go smoothly for all concerned & wish you all the best.