https://zslpublications.onlinelibrary.wiley.com/doi/abs/10.1017/S0952836901000851

Again, this cannot be replicated by any cage, this study does point to the conclusion that hamsters greatly benefit from having as deep of bedding as possible.

 

“Their structure was simple, consisting of a single vertical entrance (gravity pipe) that proceeded to a nesting chamber and at least one additional food chamber. The mean length of the entire gallery system measured 200 cm and could extend up to 900 cm.”

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https://www.sciencedirect.com/science/article/pii/S016815910500393X​

Correlates bedding depth with occurence of stress-related behaviors

 

“Although digging was found to be important in captive rodents, most golden hamsters are provided with only little material to dig. In this study, the influence of different bedding depths and acute stressors on the behaviour and welfare of golden hamsters was analysed. Forty-five male golden hamsters were assigned singly to three experimental groups with 80, 40 or 10 cm deep wood shavings. Behaviour was evaluated by continuous running wheel activity and video recordings, a series of stressors was applied after 7 and 8 weeks. Burrows, if constructed, were mapped monthly. Additionally, adrenals, testes and body mass as well as hormone levels of corticosteroids and testosterone were measured at euthanasia. Hamsters kept with 10 cm deep bedding showed significantly more wire-gnawing and a higher running wheel activity than the hamsters in the other groups. In 80 cm deep bedding wire-gnawing was never observed. Stressor application showed no significant immediate influence on behaviour. All hamsters in 40 and 80 cm bedding constructed burrows which they occupied. The body condition (body weight/body size3) was significantly higher in the animals kept in deep (80 cm) compared with those housed in low (10 cm) bedding cages. The relative testes weights were significantly heaviest in the medium treatment group. No significant differences could be detected for the adrenal glands and testosterone levels. In this study, we showed that cages with at least 40 cm of bedding seemed to enhance the welfare of golden hamsters, although those in 80 cm bedding had more body fat compared with the other groups. However, deep bedding which is appropriate for burrowing can be recommended for golden hamsters.”​

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https://www.sciencedirect.com/science/article/pii/S016815910500393X

Correlates bedding depth with occurence of stress-related behaviors

 

“Although digging was found to be important in captive rodents, most golden hamsters are provided with only little material to dig. In this study, the influence of different bedding depths and acute stressors on the behaviour and welfare of golden hamsters was analysed. Forty-five male golden hamsters were assigned singly to three experimental groups with 80, 40 or 10 cm deep wood shavings. Behaviour was evaluated by continuous running wheel activity and video recordings, a series of stressors was applied after 7 and 8 weeks. Burrows, if constructed, were mapped monthly. Additionally, adrenals, testes and body mass as well as hormone levels of corticosteroids and testosterone were measured at euthanasia. Hamsters kept with 10 cm deep bedding showed significantly more wire-gnawing and a higher running wheel activity than the hamsters in the other groups. In 80 cm deep bedding wire-gnawing was never observed. Stressor application showed no significant immediate influence on behaviour. All hamsters in 40 and 80 cm bedding constructed burrows which they occupied. The body condition (body weight/body size3) was significantly higher in the animals kept in deep (80 cm) compared with those housed in low (10 cm) bedding cages. The relative testes weights were significantly heaviest in the medium treatment group. No significant differences could be detected for the adrenal glands and testosterone levels. In this study, we showed that cages with at least 40 cm of bedding seemed to enhance the welfare of golden hamsters, although those in 80 cm bedding had more body fat compared with the other groups. However, deep bedding which is appropriate for burrowing can be recommended for golden hamsters.”
 

http://www.tandfonline.com/doi/abs/10.1080/09291010902731171

 

Indicates that low bedding depth forces hamsters to develop sleep patterns due to external lights rather than by free will

 

“In the wild, golden hamsters live in deep burrow systems, and hidings like shelters or burrows should also be available to animals in captivity. The aim of the present paper was to investigate putative effects on the circadian activity rhythm of golden hamsters with bedding material as enrichment. Three different bedding depths (10 cm, 40 cm, 80 cm) were investigated in 45 males (15 per group) kept singly. Their wheel-running activity was recorded continuously. The light–dark cycle was 12:12 h with 30-min dusk and dawn periods. Activity onsets coincided well with lights-off in low bedding depth, but in the groups with 40 and 80 cm the activity rhythms did free run with a significant increase in tau with bedding depth. All hamsters in medium and deep bedding built and lived in self-constructed burrows. It is possible the difference in light intensity between light (50–85 lux) and dark conditions (0.5–2 lux) might have been too low. As a consequence the LD zeitgeber was not strong enough to entrain the activity rhythms, though the light was bright enough to stop running at least in some animals (masking). Hamsters of the low bedding group were continuously exposed to the light–dark cycle and thus were able to synchronise their activity rhythm. We conclude that bedding depth can influence the circadian rhythm of golden hamsters which has to be taken into account when performing chronobiological studies.”

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http://www.tandfonline.com/doi/abs/10.1080/09291010902731197

 

Further proves the benefit of deeper bedding as it relates to natural sleep and activity cycles

“In a previous study, golden hamsters living in self-constructed burrows showed reduced running wheel activity and decreased activity outside the burrows compared with animals without the possibility to dig burrows. Since different activity apportionments might account for that, different activity measurements were performed to show the relationship of different parts of general activity: running-wheel activity, activity inside and activity outside the bedding. Twelve hamsters in low bedding (<10 cm) were compared with 12 hamsters in deep bedding (80 cm). To further test the synchronisation to the light system, the animals were observed under light–dark (L:D) and under constant dark (D:D) conditions. Hamsters in deep bedding were significantly less synchronised to the light system, developed longer circadian rhythms tau (τ), had later activity onsets in the running wheel and a lower running wheel activity than hamsters in low bedding cages. Their activity onsets inside the bedding were later. Time differences between the onset of movements inside the bedding and the onset of running wheel activity were not significant. Thus, the later appearance of golden hamsters kept in deep bedding was not fully compensated by more activity inside the burrows.”

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Ayars GH, Altman LC, Frazier CE, Chi EY. (1989) The toxicity of constituents of cedar and pine woods to pulmonary epithelium. Journal of Allergy and Clinical Immunology 83, pg. 610-18

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"Instillation of plicatic and abietic acids into rat lungs produced bronchial epithelial sloughing. Abietic acid also caused destruction of the alveolar epithelium. The addition of either acid to rat tracheal explants caused epithelial desquamation that was dose- and time-dependent."

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