Schneider, B. M., Erhard, M. H., Scheipl, F. et al. 2016. Comparison of 2 gentling programs for laboratory rats: Effects on the behavior toward humans. Journal of Veterinary Behavior 12, 73-81.

Gentling can reduce the fear reactions of young laboratory rats toward people long term. We were able to show this outcome in a previous study that involved a successful but elaborate gentling program. In the study at hand, we investigated whether a comparable positive effect on the behavior of rats can be achieved with a less time consuming (“reduced”) gentling program. We further determined whether the repeated testing had any influence over the rats' behavior. Thirty-six female Wistar rats, 21 days old, were allocated to an experimental, control, and zero-control groups. The experimental group was gentled once a day for 10 minutes per cage in the forth and fifth week of life. To assess the rats' behavior toward humans, the animals in the experimental and the control groups were subjected to standardized behavior tests at the sixth, eighth, 10th, and 14th week of life and at the age of 6, 6.5, and 9 months. The animals in the zero-control group were only tested at 6 months of age, so that we could compare the habituation effect to the testing procedure. The test procedure included repeated catching of the animals, a neck grip, a hand test, and a modified open-field test (with human stressor). Five primary endpoints, which summarized the most important parameters for the assessment of “tameness” toward humans, were used for the evaluation of the results. The results were compared to those of the “intensive” gentling of the previous study. Up to an age of 4 months, the estimated differences between the experimental and control group of the “reduced” gentling program were significant (P < 0.05), suggesting a higher level of “tameness” in the gentled rats. The control group habituated to the testing procedure and therefore achieved higher values over time. Comparing the “intensive” gentling program with the “reduced,” there were no significant differences in the primary endpoints up until the age of 22 weeks. After that, the “intensive” gentling produced better results regarding “tameness.” There was no significant effect of elapsed time between subsequent tests in the “intensive” gentling group, whereas the effect of elapsed time was pronounced in the “reduced” gentling group. These results indicate that the “intensive” gentling had a more persistent effect in the absence of frequent interaction with humans than the “reduced” gentling. The reduction of the time-consuming “intensive” gentling program resulted in shortening the “tameness” effect from 6 to 4 months.