Lots of people mix altered rats. There shouldn't really be a problem Most of the time though I hear of grouping them when it's the males that were neutered.
We have our sweet Oreo. She developed a mam tumor at 16mo. Which according to articles I've read, females will most often get them at the beginning of menopause then again around 2yrs old. It looks like O'ey was one of those menopause girls. I took her to the vet mostly to have it confirmed. Due to her age and on advice of the vet, we decided not to have it removed. Often those tumors just come back. There is evidence that spaying will reduce the chance of getting them. I think I read that approx 50% of females will get them. Our vet charges $350 to remove tumors. Ouch. Then the gals may not make it through anesthesia. And as I said they often recur. I do have vets that deal with these little creatures a lot, so I trust their judgment. It's now 4mos since the tumor appeared and we are just now seeing it affect her some. We'll keep a watch on her and if things get worse.....
If you are getting a good rate on spaying them all, I'd probably do it too. Just so much heartache, ya know.
We just got 5 boys. I don't think we'd neuter them unless we saw some severe aggression issues. They are only 2mos old. I hope we don't.
boys: cadoo, cosmo, jinx, moe, ziggy
girlies: sox, chops
gone: Inky--2/7/07 Oreo 4/1/07