Effect of Sequence of Pregnancy on Litter Size and Growth in Peromyscus Polionotus

Abstract

An analysis of 143 litters of Peromyscus polionotus showed that litter size increased by 0\m=.\30 mice/litter up to the fourth pregnancy. After the fourth litter, litter size increased at a lesser rate to the sixth pregnancy. Growth followed the same general pattern as did litter size. The effect of order of litter was significant for weights up to 28 days of age. In general, average weight of the mice increased up to the sixth pregnancy and then decreased. Litter size and growth of laboratory mice {Mus musculus) are influenced by a variety of environmental and genetic factors including the number of the litter in the sequence of pregnancies of an individual female. Bittner (1936) presented data which showed a maximum litter size at the third litter. Grüneberg (1952) * Journal Paper No. 391 of the College Experiment Station of the University of Georgia, College of Agriculture Experiment Stations. This research was supported in part by Atomic Energy Commission Contract AT (40-1)2975. 257