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

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 measuringweight 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

Nesting material and number of females per cage: effects on mouse productivity in BALB/c, C57BL/6J, DBA/2 and NIH/S mice

Two different materials-aspen wood-wool and paper towel-were compared as nesting material for three inbred mouse strains (BALB/c, C57BL/6J and DBA/2) housed in barrier conditions. In addition, the effect of varying the number of females per cage (one to three per cage) of these three strains and with NIH/S outbred mouse stock was studied. The number of litters, litter size and neonatal mortality were determined, as well as age, sex and weight of weanlings. The type of nesting material did not affect the characteristics monitored. In all strains, the number of weanlings per female was greatest in singly-housed females. In terms of the number of weanlings per cage, two females per cage gave the best result. In DBA/2 mice, neonatal mortality increased when several females were caged together

Aspen wood-wool is preferred as a resting place, but does not affect intracage fighting of male BALB/c and C57BL/6J mice

Aspen wood-wool, provided as nesting material, was evaluated as a possible improvement of cage environment for 1O-14-week-old inbred male mice maintained in groups of six IBALB/c n = 72 and CS7BL/6J n = 36). The daily behaviour of mice was video recorded and their body weight, food consumption, weights of some organs and serum corticosterone concentrations were measured. Aggressive interactions between cage mates and against a strange intruder as well as the number of wounds on the back of the animals was monitored in order to evaluate the effect of nesting material on intermale aggression. Nesting material did not affect the daily active/passive behaviour patterns of mice, although animals clearly preferred it as a resting place. BALB/c mice given nesting material showed less weight gain and smaller brown adipose tissue weights than animals without nesting material. The other characteristics measured were not affected by the presence of nesting material in either strain. The presence of nesting material had no effect on fighting in cages. CS7BL/6J mice were more aggressive than BALB/c mice according to the number of wounded animals in a cage. Wounded BALB/c mice had enlarged spleens and decreased epididymal adipose tissue weights. In conclusion, the nesting material used in this study did not adversely affect the animals. On the other hand, the material was clearly preferred to conventional bedding as a resting place. These findings suggest that nesting material may improve the cage environment of laboratory mice. Furthermore, there was an indication of strain differences in aggressive behaviour. It could be suggested that C57BL/6J mice are less tolerant towards intruders and housing six mice per cage is not suitable for this strain

Estimates of Appropriate Number of Rats: Interaction With Housing Environment

An extensive list of physiological parameters from previous experiments was re-analysed in order to evaluate the effects of enrichment, cage type and group size on the within-group variation and hence on the number of animals needed in studies using Wistar rats. The independent factors studied in these experiments included the provision of aspen gnawing blocks for enrichment, solid bottom cages (SBCs) and grid ¯oor cages (GFCs) and animal number per cage (varied from 1±4). SOLO power analysis was used to calculate the smallest number of animals (n) needed to detect an arbitrarily chosen 20 % effect size, when signi®cance was set at P ˆ 0.05 and statistical power at 0.90. N ratios (n larger=nsmaller)were calculated for the effect of enrichment, cage type and group size to compare the `treatment group ’ with the `control group’. The n values of adrenal gland, interscapular brown adipose tissue (BAT) and epididymal adipose tissue (EAT)weights seemed to varymost, whereas ®nal body weight (FBW) and growth seemed to be the least variable ones. According to one-sample t-test, the N ratios of most physiological parameters differed signi®cantly from zero (except the ones of FBW) indicating that n values in `treatment ’ and `control ’ groups were unequal. The results indicate that some of the physiological parameters are susceptible to variability attributable to environmental modi®cations in general whereas some are not. Furthermore, they suggest that the variation of different parameters may vary from one experiment to another and between different environments thus hindering the estimations of appropriate number of animals