So where does that leave a bitch who lactates through phantom pregnancies?

Digger I would suspect that because the same hormones would be in action whether the lactation was caused through an actual pregnancy or a phantom, and would therefore offer the same amount of protection. Phantoms being a natural state of the female dog.

I guess my Bonnie was extremly unlucky then - she had mammary tumours inspite of having regular phantoms :(

There are always exceptions Digger, spayed bitches and in fact males also get mammary cancer. The likelihood of a spayed bitch, a whelped bitch and a male is less than an un-whelped intact bitch. Just as in humans, to avoid it in the human the breast is removed not the womb and ovaries.

Got it now. I expect it was my mistake! :o

Cant be that protective. Ruby's been pregnant or nursing ALL of her adult life and now has this killer cancer - just like many many older unspayed bitches, whether used for breeding or not. I think its irresponsible of some sites to use that as an excuse for breeding and not spaying.