Seasonal variation in litter size, bodyweight and sexual maturation in juvenile female house mice (Mus musculus).

Over a 4-year period a higher proportion of mated females bore litters during spring and summer than in late autumn and winter. Litter sizes were larger and young female mice weighed more at 21 days of age during spring and summer than at other times. However, young females attained sexual maturity, as indicated by vaginal smears, earlier during the winter months. This contrasts with data indicating that pubertal female mice have lower uterine weights in winter, A multiple regression analysis revealed that mouse bodyweights at 35 days of age and at 1st oestrus were important variables for predicting the age of puberty. Possible factors influencing reproductive seasonality in female house mice maintained under laboratory conditions are discussed.