Effects of gnawing material, group size and cage level in rack on Wistar rats

Abstract

Han: Wist rats were housed after weaning in groups of one, two, three or four in stainless steel cages with aspen chip bedding, with or without wooden gnawing blocks. The use of the blocks was assessed by Video recording and by measuring
weight loss of the blocks. Behaviour of the males  was tested in a five minute open field test. At the age of 14 weeks the males were transferred into cages with wire mesh bottom without contact bedding. After four weeks, the males were  euthanized and weights of the adrenal glands, thymus and spleen were measured. The physiological and behavioural effects of blocks, group size and cage level in rack were tested. In solid bottom cages with direct bedding, the use of the blocks was minimal. It was not affected by the sex or age of the animals. Neither was it affected by the group size or the cage level in a rack. The gnawing of the blocks increased afier the rats were transferred on to grid floor without bedding. The food intake or weight gain were not affected by any of the factors studied. The presence of blocks decreased the adrenal weights in rats transferred into wire mesh cages. In open field, the animals living alone were less active and they moved slower from the peripheral to central area than the animals living in groups. The animals living on the highest shelf of the rack differed from the others in their latency times of rearing and grooming. None of the environmental variables tested affected the behavioural factor scores derived from factor analysis. In conclusion. the wooden blocks may reduce the stress of rats adapted to bedding, if they have to be removed to grid floor. The group size or cage level in rack influenced some behaviours of rats in the open field.