Interesting topic… And good point CYJ about high strung hard keeper type bitches.
I have a 3 yr old Hollingsworth/Patricks bitch, and after at least 2 of her heats she's had a false pregnancy. No mastitis as of yet, but I watch for it. She has regular heats, then 2 or 3 weeks after her heat (she's never been bred) she gets swollen teats and starts hiding in closets and corners. Darnedest thing, I was really stumped when it first happened. She's a house pet, and is pretty high strung, but I give her a lot of exercise which helps.
I was told to cut her food a bit and to start working her some when she gets this false pregnancy thing. I also take her in the car more and it seems to help, giving her something else to think about. But it was pretty funny to see her sitting in a corner behind the furniture, or in the closet.
I was warned to keep an eye out for her possibly getting pyometra. Apparently there is a tendency for bitches that are not bred and that get false pregnancies to get an infected uterus, i.e. pyometra. I'm not sure what, if anything, one can do to prevent that, outside of breeding the bitch, but thought I'd mention it.
Just for fun, here's a photo of her sitting in the corner last year.