So I seem to have alot of impotent rats.

I have 6 breeding tubs with 1.3 in all except two wich holds 1.2, I have had them for about 3 weeks now and I have yet to see a fat belly on any of them.

They are located in my snake room, ambient temp around 80F. They are in a rack, cat litter pan sized tubs, always access to food and water.

Am I doing something wrong? I mean breeding rats is pretty straight forward? My mice breed like crazy, but my rats do not...

Do rats need time to acclimate to their new home or something? Do I need to be patient?

Appreciate any help
Thanks