Multiple reports of overstocking have been reported. Users should be aware of the minimum space required for each animal, and make appropriate plans to separate cages when breeding involved.
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Case study: Overstocking cagesAreas of concern
1. Welfare of animal: 5 freedoms- Animal should be free from discomfort due to environment, and space to express normal behaviour. 2. Ethical and legal issues: breach of University regulations (and AAALAC requirements) for cage capacity. 3. Data reliability: Crowded cages induce animal stress, causing variability of data. 4. Labour and economic costs: Increase bedding change frequency, increase feed waste 5. Damage to the reputation of yourself and PI, and the University. |
LASEC regulation on caging numbers |
MICE: Mice over 21 days old are considered weaned and should be separated. Large cage: 10 mice; small cage: 5; IVC cage: 5
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Why my results will be affected by the overcrowded cage?
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Animal Aggression: A study interviewed 143 animal technicians in 44 facilities found the standard number of mice housed per cage can affect the level of aggression[1]. Additional evidence suggests housing mice in 3-5 groups avoid aggression[2]–[4].
Food & Fluid intake: Food intake and weight changes as measurable outcomes may be impacted by crowded cage. A study found increase group size was associated with decrease food and fluid intake[5], likely due to aggression. Corticosterone level: Corticosterone as a stress biomarker may be measured in behaviour studies and depression models. Plasma corticosterone level was found to be negatively correlated with cage floor space in C57BL/6 males[6]. Temperature & humidity: The number of animals in a cage influences the intracage environment, especially temperature and humidity[7]. Difference of 5oC and 40% in humidity were recorded between cage of 5 and cage of one animal[7]. Ammonia levels: Cages with mice and offspring can reach high ammonia levels to 200ppm comparing to cages without offspring at 50ppm after 1 week[8]. Nasal histopathologic changes including epithelial necrosis and mucosal inflammatory infiltrates can be observed, with severity associated with ammonia levels (R2=0.64)[8]. |
References
[1] K. Lidster, K. Owen, W. J. Browne, and M. J. Prescott, “Cage aggression in group-housed laboratory male mice: an international data crowdsourcing project,” Sci. Rep., vol. 9, no. 1, pp. 1–12, Dec. 2019, doi: 10.1038/s41598-019-51674-z.
[2] P. Jirkof, N. Bratcher, L. Medina, D. Strasburg, P. Ebert, and B. N. Gaskill, “The effect of group size, age and handling frequency on inter-male aggression in CD 1 mice,” Sci. Rep., vol. 10, no. 1, Dec. 2020, doi: 10.1038/s41598-020-59012-4.
[3] A. Haemisch and K. Gartner, “Effects of cage enrichment on territorial aggression and stress physiology in male laboratory mice,” Acta Physiologica Scandinavica, Supplement, vol. 161, no. 640. 1997.
[4] P. L. P. Van Loo, J. A. Mol, J. M. Koolhaas, B. F. M. Van Zutphen, and V. Baumans, “Modulation of aggression in male mice: Influence of group size and cage size,” Physiol. Behav., vol. 72, no. 5, 2001, doi: 10.1016/S0031-9384(01)00425-5.
[5] J. D. Bailoo, E. Murphy, J. A. Varholick, J. Novak, R. Palme, and H. Würbel, “Evaluation of the effects of space allowance on measures of animal welfare in laboratory mice,” Sci. Rep., vol. 8, no. 1, 2018, doi: 10.1038/s41598-017-18493-6.
[6] S. Fullwood, T. A. Hicks, J. C. Brown, R. L. Norman, and J. J. McGlone, “Floor space needs for laboratory mice: C57BL/6 males in solid-bottom cages with bedding,” ILAR J., vol. 39, no. 1, pp. 29–36, Jan. 1998, doi: 10.1093/ilar.39.1.29.
[7] L. A. Toth, R. A. Trammell, and M. Ilsley-Woods, “Interactions between housing density and ambient temperature in the cage environment:effects on mouse physiology and behavior,” J. Am. Assoc. Lab. Anim. Sci., vol. 54, no. 6, pp. 708–717, Nov. 2015, Accessed: Jun. 11, 2021. [Online]. Available: /pmc/articles/PMC4671786/.
[8] A. M. Mexas, A. K. Brice, A. C. Caro, T. S. Hillanbrand, and D. J. Gaertner, “Nasal histopathology and intracage ammonia levels in female groups and breeding mice housed in static isolation cages,” J. Am. Assoc. Lab. Anim. Sci., vol. 54, no. 5, pp. 478–486, Sep. 2015, Accessed: Jun. 11, 2021. [Online]. Available: https://www.avma.org/KB/Policies/.
[2] P. Jirkof, N. Bratcher, L. Medina, D. Strasburg, P. Ebert, and B. N. Gaskill, “The effect of group size, age and handling frequency on inter-male aggression in CD 1 mice,” Sci. Rep., vol. 10, no. 1, Dec. 2020, doi: 10.1038/s41598-020-59012-4.
[3] A. Haemisch and K. Gartner, “Effects of cage enrichment on territorial aggression and stress physiology in male laboratory mice,” Acta Physiologica Scandinavica, Supplement, vol. 161, no. 640. 1997.
[4] P. L. P. Van Loo, J. A. Mol, J. M. Koolhaas, B. F. M. Van Zutphen, and V. Baumans, “Modulation of aggression in male mice: Influence of group size and cage size,” Physiol. Behav., vol. 72, no. 5, 2001, doi: 10.1016/S0031-9384(01)00425-5.
[5] J. D. Bailoo, E. Murphy, J. A. Varholick, J. Novak, R. Palme, and H. Würbel, “Evaluation of the effects of space allowance on measures of animal welfare in laboratory mice,” Sci. Rep., vol. 8, no. 1, 2018, doi: 10.1038/s41598-017-18493-6.
[6] S. Fullwood, T. A. Hicks, J. C. Brown, R. L. Norman, and J. J. McGlone, “Floor space needs for laboratory mice: C57BL/6 males in solid-bottom cages with bedding,” ILAR J., vol. 39, no. 1, pp. 29–36, Jan. 1998, doi: 10.1093/ilar.39.1.29.
[7] L. A. Toth, R. A. Trammell, and M. Ilsley-Woods, “Interactions between housing density and ambient temperature in the cage environment:effects on mouse physiology and behavior,” J. Am. Assoc. Lab. Anim. Sci., vol. 54, no. 6, pp. 708–717, Nov. 2015, Accessed: Jun. 11, 2021. [Online]. Available: /pmc/articles/PMC4671786/.
[8] A. M. Mexas, A. K. Brice, A. C. Caro, T. S. Hillanbrand, and D. J. Gaertner, “Nasal histopathology and intracage ammonia levels in female groups and breeding mice housed in static isolation cages,” J. Am. Assoc. Lab. Anim. Sci., vol. 54, no. 5, pp. 478–486, Sep. 2015, Accessed: Jun. 11, 2021. [Online]. Available: https://www.avma.org/KB/Policies/.