Here is a good article that discusses the pros and cons of spaying and neutering.
http://www.naiaonline.org/pdfs/LongT...uterInDogs.pdf
I recommend any female that is not going to be bred should be spayed but I am not an advocate of early spaying. I think for the health of the female it is better to wait until they are a little more mature. There is a lot of research and responsibility that goes into breeding. There are risks no mater what you decide to do. I do wish you the best.