Colony differences and behavior in Long-Evans rats

Abstract

A series of three experiments was performed on male Long-Evans rats from two colonies, Blue Spruce Farms (BSF) and Mississippi State University (MSU). The purpose of the present study was to account for the differences in rate of mouse killing by male Long-Evans rats from different colonies reported by Thompson and Thorne (1975). A pilot study replicated the findings of Thompson and Thorne. Experiment I found that the offspring of animals whose parents were obtained from BSF and bred at MSU killed at a significantly higher rate than animals whose parents were part of the MSU breeding stock. Thus, genetic and/or preweaning variables were implicated in accounting for the results reported by Thompson and Thorne. Experiment II found no differences between BSF offspring (mostly killers) and MSU offspring (mostly nonkillers) on measures of handling characteristics, activity, and learning of a simple discrimination task. Experiment III was intended as a replication of Experiment I, but no differences in the rate of killing were found between BSF and MSU rats. Due to methodological flaws, the present study was unable to account for the differences seen by Thompson and Thorne (1975). Possible explanations for the failure of Experiment III to replicate Experiment I were discussed.