Toby, great post. I figured the meahllmorum would be partially active in s. TX in winter. I may cool them around 60* for a few weeks and see how they do, then maybe go for a month or two. The BI rats are doing great, so far. Good luck with yours this winter and keep us posted 
The clutch info is very valuable. Thanks for the pics too. Those are nice looking babies and look a lot like the adults. I did a cross bt. an adult, male, BI rat and a hypo corn. The results were interesting with about a dozen eggs. I only have one baby from that first clutch still, and it's a subadult female.
I think many of the Great Plains rats do have small clutches and yours are having an inbetween size. (I'm not sure what the size ave. is for the BI rats.) This is an indicator of intergradation, imo, and is good info that most others have not reported on much. Not many folks think there is intergradation between meahllmorum and slowinskii. Heck, they aren't sure whether slowinskii is guttatus or it's own species. We're still waiting for some people to publish on this. Keep up the good work on that.
Thanks for the report. Later....TC