Date of Award


Document Type


Degree Name

Master of Arts



First Advisor

Frederick J. Kozuo


The effects of the early experience variable of litter size is examined at two developmental time periods (infancy and adulthood) in the rat. The study departs from the majority of the early experience experimentation in its use of a naturally occurring independent variable in place of the typical handling and shocking procedures. Large (n = 9), medium (n = 5), small litters (n = 3) were developed by pooling rat pups at birth and then distributing them to randomly selected, lactating females. Observations of behaviors (including maternal grooming) during the preweaning stage of development disclosed substantial differences in response activity in the three litter size groups. Weaning weights also varied significantly across the experimental groups. Generally, the results of infant behavior observations and weights indicated that the medium litter size was the most efficacious in terms of development and weaning weights. The findings obtained from the observations of infant behaviors were attributed to differences in environmental stimulation afforded by the three rearing conditions. Analysis of adult open field behaviors (i.e., ambulation and defecation) failed to reveal any variation between the experimental groups. Adult weights also did not differ. Results were interpreted associatively. Strain differences, age of adult testing, and the testing situation were also discussed as possible factors influencing the results. And, conceivably, the conclusion that litter size effects were transitory and disappeared in adulthood can be made.

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Psychology Commons