i've heard several times that birthing racks are the way to go, so I started a few months ago with a trial run... Way more production, I'm switching all my rats over to a birthing rack as soon as I get it built.
I tried it with 28 tubs, and my numbers went way up over the 3 months I tried it. i left all my other rats in 1.2 lab cages. I was impressed how many babies I produced in just 28 tubs over such a short time. Less deaths, cleaner, and less stress on the mommas. Although, it is a bit more work to move them around. But, i found that for the first two weeks after birth, you don't even have to clean the tubs out, so that's a major plus.
So, I just bought 70 more tubs and watering valves... Now I just gotta find the time to build build build...
My harem racks are getting disassembled for parts.