SIGNIFICANCE OF WEANING PERIOD FOR NATALITY AND MATERNAL-BEHAVIOR OF LABORATORY RATS

Abstract

Normally weaned females [at 30 days] displayed seasonal cyclic changes in natality and the characteristics of the young. Natality in the spring and summer was high, the litters were large the proportion of females and males in the litter was equal and deaths among unweaned young were very few. Natality in the autumn and winter was low and the litters were small and consisted mainly of males. The death rate among the young was higher than in the spring and summer. Prematurely weaned females [at 15 days] displayed no seasonal cycle either in natality or in the characteristics of the young. The studied parameters corresponded to the values found in the spring and summer in normally weaned females. No differences were found in maternal retrieving, but there was a marked difference in nest-building. The normally weaned female tore up paper (building material) into small fragments 24 h before giving birth and dropped the young into a soft nest of finely shredded paper. On leaving the nest it covered the young up. The prematurely weaned female scattered the paper about the cage 24 h before giving birth and dropped the young into a depression stamped out among whole pieces of paper. It did not cover the young up on leaving the nest. Prematurely weaned females apparently failed to acquire early experience of this behavior between the 15th and 30th day of life.