The effects of parity, litter size, season, and breeding protocol on the number of DBA/2J Ten mice available for weaning.

Data on the reproductive behavior of DBA/2J Ten mice, collected from October 1970 through March 1973 and utilizing a 2-female, 1-male breeding system, with the mice remaining together throughout their reproductive life indicates: a) Litter size tends to increase through the fourth litter, the first litter being much smaller than successive litters; b) Survival rates of litters with 2--4 pups increase with successive deliveries; c) Survival rates of litters with 5--9 pups are approximately the same regardless of parity; d) There is a circannual rhythm in the number of pups available for weaning da 21, which is attributable to changes in postnatal viability. Data collected using a breeding pen system, with isolation of females pre- and post-delivery (March 1973 to March 1974) indicates: a) There is a reduction in live litter sizes in later litters with this system; b) There is a large reduction in the proportion of pups surviving to weaning with this system when compared with the other breeding system.