Eskola, S., Kaliste-Korhonen, E. 1998. Effects of cage type and gnawing blocks on weight gain, organ weights and open-field behaviour inWistar rats. Scandinavian Journal of Laboratory Animal Science 25(4), 180-193.

Two separate experiments were conducted to study the environmental enrichment value of aspen gnawing blocks in solid bottom cages with bedding '(SBC) and in grid floor cages without bedding (GFC), and the effects of housing environments on the physiology and behaviour of male outbred Wistar rats (n=90). Animals were housed in groups of 3 from weaning until the age of 8-12 weeks. The behaviour of animals in the first experiment was tested in five minute open-field tests at the age of 8 and 12 weeks. Rats gnawed blocks about four times more in GFCs than in SBCs (p<0.01). In the first experiment, animals housed in GFCs had heavier adrenal glands (p<0.001) but lower serum corticosterone concentrations (p<0.01) and their weight gain was greater than animals housed in SBCS (p<0.000). The presence of blocks in cages decreased the weight gain in both cage types (p<0 001) In the first open-field test, the animals without blocks in both cage types decreased their activity in the central area during the last 2.5 min of the test (p<0.01). The similar effect of blocks was also seen in animals later transferred into GFCs (p<0.05). These rats without blocks were also less active in the periphery (p<0.01) and had more standing alert behaviour (p<0.01) than animals with gnawing blocks. In both open-field tests, rats housed in SBCs showed more grooming behaviour than animals in GFCs (p<0.05). In the second experiment. animals in GFCs had again enlarged adrenals (p<0.05) and their brown adipose tissue weights were slightly increased (p<0.05) Altogether, SBC as a living environment resulted in lighter animals with smaller adrenals. but higher serum corticosterone concentrations. In the open field, blocks seemed to result in more active and less timid animals and antagonize the effects of housing in GFCs. Aspen gnawing blocks can be recommended as enrichment objects especially in GFCs.