Effects of Litter Origin and Weight on Behaviour of Outbred NIH/S Mice in Plus-maze and Staircase Tests

  • Kai Õkva Vivarium University of Tartu
  • Aavo Lang Department of Physiology, University of Tartu
  • Timo Nevalainen National Laboratory Animal Center, University of Kuopio and Department of Basic Veterinary Sciences, University of Helsinki
  • Kari Mauranen Department of Mathematics and Statistics, University of Kuopio
  • Marika Väli Department of Pathological Anatomy and Forensic Medicine, University of Tartu
  • Paavo Pokk Department of Pharmacology, University of Tartu


The objective of this study was to investigate the effects of litter and weight on the behavior of mice.  Male outbred NIH/S mice from 8 litters were randomly distributed among 6 cages and subjected to the  plus-maze and staircase tests. The litter from which the animals had originated had a significant effect on  the behavior of mice in the plus-maze test; furthermore addition of the covariates final weight and weight  gain had no effect on significance or explanatory value. It is proposed that litter origin might influence the  adaptation processes, the development of social status and consequently, the behavior of mice. Differences  attributable to litter were not observed in the staircase test, but when both weight parameters were added as  covariates this proved to be significant. Though the source of these litter-related differences remains to be  clarified, these differences do have a significant effect on the behavior of mice. Therefore they need to be  considered since knowledge of the litter where the outbred mice originated can partly explain differences in  the behavior of the animals. The comparison of models showed that incorporation of the natural features of  the animals (as derived from their biological origin) into a calculation can help rationalise the results; and  provide ample opportunities for discussion and understanding of this complex issue.