| Abstract
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Environmental enrichment such as the addition of shelters in otherwise empty cages can improve the welfare of laboratory animals. In the first chapter, we tried to establish the preference of Syrian hamsters (Mesocricetus auratus) for different types of shelter. First, 15 males and 15 females were offered a choice between a cage with a shelter and one without. The shelters were an Acrylonitrile Butadiene Styrene (ABS) pipe 7.6 cm in diameter open at both ends, either short (10 cm) or medium length (15 cm), as well as an acrylic box open at one end only, either short (10 cm length x 7.6 cm height x 7.6 cm width) or medium length (15 cm length x 7.6 cm height x 6 cm width). Both males and females preferred the cage with the medium length open pipe. Hamsters used the medium length open pipe for nesting more often than the short open pipe (22/30 versus 2/30 hamsters). A second experiment gave a choice between pairs of shelters for 10 males and 10 females. The seven different shelter types used in this experiment were: open medium ABS pipe (15 cm), open long ABS pipe (20 cm), semi-closed (closed at one end) medium ABS pipe (15 cm), semi-closed acrylic box (15cm x 7.6 cm x 7.6 cm), aluminium cover (15 x 24 cm), running wheel (35 cm diameter), and a deep layer of litter (10 cm instead of 1 cm). Both sexes preferred nesting in the semi-closed ABS pipe rather than under a wheel (P < 0.05). There were tendencies for both sexes to choose a semi-closed pipe over a medium open pipe (adjusted P = 0.09) and the females tended to nest in the semi-closed pipe rather than under an aluminium cover (adjusted P =0.06). The goal of the second chapter was to discover if the presence of a shelter in a cage with litter 3, 9 or 14 days old would keep hamsters from nesting in a clean litter cage when such is made available. Out of 15 male hamsters, 10, 11, and 8 never nested in the new cage after 3, 9, and 14 days in an old cage respectively, whether the old cage had a shelter or not. Of those that used the new cage at least once, 3 out of 5 (lifter age of 3 days), 3 out of 4 (litter age of 9 days) and 5 out of 7 (litter age of 14 days) nested in the new cage less often when a shelter was present in the old cage (P = 0.11 on a signed rank test). These results reveal a relative lack of new cage use for nesting even after 14 days in the same old litter, and almost a statistical tendency (P = 0.11) for the expected attraction of the shelter in litter 9 and 14 days old. The difference between the clean litter volume at the start and at the end of the period was significantly higher for the 9 and 14 day conditions than for the 3 day condition (P<0.001) and tended to be higher when the shelter was present (P = 0.08). This indicates that litter could be transferred between cages and could help explain the infrequent use of the clean litter cage for nesting. Overall, a semi-closed 15 cm ABS pipe seems preferred by the Syrian hamsters. A recommendation for its use could thus be made, adding that this type is relatively easy to clean as well as fairly inexpensive. Keywords: animal welfare, shelter, environmental enrichment, Syrian hamster, litter
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