I have the same rack as Deborah posted (kind of stole her design), I haven't really tried without it, as I was always pulling moms away even back with the ARBreptiles rack designs. Since I switched to a litter pan breeding rack, I always use the "birthing" rack, just because it's there, but in the near future I plan on building a rack akin to jasbus' rat rack and seeing if I notice any difference.

Only thing that I really like about the birthing rack idea is that I tag the front of the tubs when the litter was born so I can keep track of ages of rats and know approx wean times without having to go on size. This is due to what I've noticed that a mom with a larger litter will have smaller babies vs a mom with a smaller litter.

WHEN my moms give birth in the breeding rack (happens more than it should, but oh well), I don't notice any fighting over babies, and last week I actually had 3 moms give birth and put all their pinks in 1 big pile. When I got around to pulling them for the birthing rack, I just split the pile up by the numbers (31 pinks, so 10 to each mom and the largest one got the 1 left over), all were accepted and are currently in "chub" stage.