I've wondered about breeding life as well but I generally replace all the adults at 12 to 14 months anyway.
Interesting stuff.
I find deadfornoreason babies from time to time as well. It's usually from a first time mother, I think, or the heat spikes. Even with A/C we still get some hot days here.
I've also noticed in the last 6 months or so, that's all I've been keeping records for, that in groups of 1.6 I get tons of pinks but as they get older the moms get skinny. So, if you need pinks are are pulling regularly, this is a good ratio.
At 1.5 I get lots of babies and not so skinny moms IF I leave all the babies in and nice average moms if I pull a few every week.
Lower than 1.5, 1.4 or 1.3 I get a fair amount of babies, not as many as in higher male to female ratios, as is to be expected, and everyone does just fine even if I leave all babies until weaning.
I shoot for 1.5 because I do pull some almost every week. What may be over crowded at birthing will consistently be lessened as the weeks go by but I do keep some at 1.6 just for the extra pinkies.
Moms that kill or tubs that don't produce the way I think they should are "recycled" as soon as I determine they are not up to snuff.