Effects of physical activity and group size on animal welfare in laboratory rats

The aim of this study was to investigate whether moderate physical activity and group size influence physical fitness, the level of social interactions in the home cage and rats' performance in the Elevated Plus Maze and a handling test. Forty-eight male Sprague Dawley rats were kept in groups of two, four or eight for seven weeks in cages adjusted to the group size. Home cage social interactions were studied during direct observations. Half of the number of rats from each cage were subjected to moderate exercise on a treadmill for five weeks. An exercise test was performed at the beginning and end of the experimental period, during which time lactate levels were analysed via blood sampling. Rats living in groups of four or eight performed better in the second exercise test; had more social interactions and showed more activity, open-arm entries and risk assessment in the Elevated Plus Maze test compared to rats living in pairs. The trained rats had lower blood lactate levels in the second exercise test lower bodyweight and plasma insulin levels and had a greater relative heart weight at the end of the study compared to control rats. In conclusion, rats kept in larger groups had more social interactions, a lower lactate response during exercise and showed less emotional reactivity. Moderate treadmill exercise resulted in the expected increase in the rats' physical fitness. The results show that both group size and physical activity are important factors for animal welfare,