Gina,
Good Stuff in that reference- the whole picture laid out in plain sight, for all to see. Thanks for posting this reference up, once again.

I wish all breeders were as informed and concerned about their puppies as you.
That reference in post #10 recommends spaying a prepubertal puppy at
eight weeks of age. And that recommendation is
absolute rubbish.
The actual incidence of mammary tumors in dogs is of the order of 198.0 per 100,000 females. Only half of these are malignant; the remainder (benign) are of no threat to life expectancy. Spaying a b###h between the second and fourth heat cycle, will reduce the incidence of mammary tumors by four times. So there is an anti-cancer benefit, even if spaying is delayed until full maturity is reached. Mammary tumors can be detected quite early and easily in dogs as well, further reducing the risk. However, mammary cancer can happen in b###hes spayed as puppies and also in male dogs as well. And ovarian tumors are even rarer in dogs, as noted above.
The most important health benefit of spaying has been overlooked by all the posters above- and that is in eliminating pyometra ie. literally "pus in the uterus". This uterine infection is much more common and widespread in dogs that mammary cancer. And is much more difficult to diagnose by an observant owner, which often leads to an early and unneccesary mortality, often linked to an uncontrollable bacteremia.
Natty B.