Introduction
Enlarged cage size, environmental enrichment and group housing are different ways of improving housing and welfare conditions for laboratory animals. However, this may also affect husbandry and handling as well as have implications for the animal as an experimental model. Our aim was to study the effect of a free-range housing system on the activity and welfare of the animals. In addition, human-animal interaction was investigated.
Methods
In the first experiment, 10 groups of conventionally housed adult male Sprague-Dawley rats in pairs (ST1) and 2 groups of ten rats housed in large enriched pens (PH1) were used. The rats’ perception of human interaction was tested in three behavioural tests of which two reflected common practical situations: capture and restraint whereas the third was a human approach test. In the second experiment, 32 newly weaned rats were housed either singly (ST2) or in groups of 8 (PH2) in the enriched pens. After 3 weeks locomotory activity in the home cage was recorded for 24 h. Muscular endurance was measured in an inclined plane test, in which the maximum angle of the plane at which the rat could maintain its position without falling was recorded as well as the maintenance time (max 5 min). In both studies food and water intake, body weight, urine and plasma corticosterone, plasma cholesterol and relative organ weights was measured.
Results
In both studies ST rats gained between 15-20% more weight than PH rats although food intake did not differ. ST1 rats had higher total cholesterol values and a greater relative heart weight than PH1 rats but lower urine corticosterone/creatinine ratio. These effects might be due to higher physical activity in the PH1 rats. The rats’ anticipatory reactions to handling and the reactions to restraint did not differ between groups but the ST1 rats approached a human hand more quickly than PH1 rats. This indicates underlying differences in appraisal that might not easily be detected in practical situations. The locomotory activity of the PH2 rats were greater and more diverse than of the ST2 rats. The PH2 rats scored higher on the inclined plane test both regarding maximum angle and even more pronounced in maintenance time.
Conclusions
Although further studies are needed, we conclude that housing large groups of male rats together in pens are a practically feasible alternative to conventional housing that would allow rats to behave more naturally. However, the differences in activity seems to affect body mass gain and muscle development. This change in body composition may have positive consequences both for animal welfare and for the animal when used as an experimental model.
References