Try down grading to one male and two females. I'd start with babies and raise them - they're sexually mature at 5 weeks of age, so getting the larges usually means you're getting old rats. Depending on the petstore and where they get their feeders, there's a pretty good chance the large rats at your petstore are just ex-breeders - and that's why they're large.



Try getting a younger trio. I know I've had success by getting smalls, raising them myself for a month (time to settle in and get used to surroundings, etc), and then introducing a male that I got at around the same time.



Side note on Nutrition - I've had much greater success and much healthier rodents (and gigantic litters - my female mouse had 14 babies her first time!) by giving them leftover people food and some bones every so often.



As far as sterilizing the rats before they get to the petstore - unlikely. Costs money to sterilize an animal, and they're not gonna make enough profit ona 6 dollar rat to want to spend money sterilizing it before it gets sold.



~jenny
-----
"The python has, and I fib no fibs,

318 pairs of ribs.

In stating this I place reliance

On a seance with one who died for science

This figure is sworn to and attested,

He counted them while being digested."

~Ogden Nash



jenny.thegreenes.org



"If you're happy and you know it,

Bomb Iraq!

If you cannot find Osama,

Bomb Iraq!

If the terrorists are frisky,

Pakistan is looking shifty,

North Korea is too risky,

Bomb Iraq!

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