Building a Colony - A few questions

[sassy-pants]

If you have 18 females and only getting 40 offspring, something is very wrong.

I get 40/month with my rack on a 12 week cycle. The male is in each tub 2 weeks before being moved into the next one. I'm averaging 7-10 pups per female (often times well into the teens), and for calculations sake I use 7 pups x 3 females per tub = 21 pups every 2 weeks, so if 1 month is 4 weeks, I get about 42 pups dropped in the rack each month. That's how I landed at my number of 40/month.

I obviously get much more than 40 rats out of 18 females, but I give my females time to rest between breedings. 2 weeks estrus, 3 weeks gestation, 4 weeks nursing, and 3 weeks rest between breedings. I have several racks going on this cycle, it is a very common one, and I have been very successful with it.