TABLE 3.
Summary of density studies using nonbreeding adult mice in static and ventilated cage systems
| Floor space/mouse |
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|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Reference | Year | Study focus | Cage ventilation | Mouse strain | Mouse details | Cage size, in2 (mice/cage) | Cage size, cm2 (mice/cage) | Fold-density vs. Guide | End points | Density-dependent differences | Trend of difference (P < 0.01) | Interpretation |
| Smith et al. (40, 41) | 2004, 2005 | Density and cage floor space | IVC | C57BL/6J, BALB/cJ, NOD/LtJ, FVB/NJ | 3 densities; 3 cage types; 2-mo study; both sexes | ∼12.5 (4, 5, 9); ∼8.6 (6, 8, 13); ∼6.6 (8, 10, 17); ∼5.6 (9, 12, 20) | 81 (4, 5, 9); 55 (6, 8, 13); 43 (8, 10, 17); 36 (9, 12, 20) | 1.0×; 1.5×; 1.9× | Weight, food and water consumption, injury, aggressive behavior, survival, testosterone, cage microenvironment | Fighting in FVB/NJ males | Greater aggression in all densities and cage types for FVB/NJ males | All but FVB/NJ males can be housed near twice the density specified in the Guide |
| Smith et al. (40) | 2004 | Density and cage floor space | IVC | C57BL/6J | Weaning cage; 4 densities; 4-wk study; both sexes | 5.6 (20); 4.5 (25); 3.8 (30); 3.2 (35) | 36 (20); 29 (25); 25 (30); 21 (35) | 2.2×; 2.8×; 3.3×; 3.9× | Same as above; add nasal and eye histology | Ammonia concentrations | Ammonia concentrations exceeded acceptable levels for the 2 highest densities (3.8 and 3.2 in2/mouse) | B6 mice in weaning cages can be housed at up to 2.8 times the density specified in the Guide |
| Laber et al. (45) | 2008 | Density and cage floor space | IVC | C57BL/6NCrl, BALB/cAnNCrl | 3 densities; 70-d study; 3 time points; females only | 37.5 (2); 15.0 (5); 7.5 (10) | 242 (2); 97 (5); 48 (10) | 0.3×; 0.8×; 1.7× | Weight gain, corticosterone, behavior, immune parameters | Weight gain | Lower at highest density (BALB) | Increased core temperature in mice at higher densities may reduce metabolic demand for food, resulting in lower consumption and less weight gain1 |
| Plasma corticosterone | Higher at highest density (BALB), but Whitaker et al. suggest both strains higher at highest | |||||||||||
| Immune parameters | CD4 + T Cells lower in highest density (BALB) | |||||||||||
| Nicholson et al. (44) | 2009 | Increased housing density | IVC | C57BL/6J, BALB/cJ | 3 densities; 4-mo study; both sexes | 12.9 (4); 8.6 (6); 6.5 (8) | 83 (4); 55 (6); 42 (8) | 1.0×; 1.5×; 1.9× | Growth, body composition, hematology, hormones, metabolites, telemetry, behavior, fecal corticosterone, adrenal glands, cage microenvironment | Weight gain | Lower at highest density (B6m; BALB f, m) | Increased cage temperature in mice at higher densities may reduce metabolic demand for food, resulting in lower consumption and less weight gain |
| Heart rate | Lower at highest density (BALB only) | May indicate reduced stress | ||||||||||
| Exploratory behavior | Lower at highest density | Uncertain | ||||||||||
| Rearing | Lower at highest density | Uncertain | ||||||||||
| Fighting | Higher at lowest density (BALB males) | Higher density may resolve aggression in BALB | ||||||||||
| Self-grooming | Higher at lowest density | Larger groups may groom each other more | ||||||||||
| Relative humidity | Higher at lowest density | Unexpected | ||||||||||
| Whisker picking | Higher at highest density (B6) | Typical B6 behavior | ||||||||||
| Temperature | Higher at highest density | Expected | ||||||||||
| C02 | Higher at highest density | Expected | ||||||||||
| Paigen et al. (46) | 2012 | Increased housing density | IVC | C57BL/6J | 2 densities; 9-mo study; both sexes | Growth, blood chemistries, body composition, EKG, aggression, barbering, mortality, food and water consumption, adrenal weight | Hematology: CHCM | Higher at higher density | Within physiologic normalcy; acceptable | |||
| Cage temperature | Higher at higher density | Expected | ||||||||||
| Cage ammonia | Higher at higher density | Expected; did not exceed acceptable thresholds | ||||||||||
| EKG: heart rate | Lower at higher density | Indicates reduced chronic stress | ||||||||||
| Food consumption | Lower at higher density | Expected | ||||||||||
| Body weight | Lower at higher density | Expected | ||||||||||
| Adrenal weight | Lower at higher density | Indicates reduced chronic stress | ||||||||||
| Morgan et al. (48) | 2014 | Increased housing density in 5 strains | IVC | 129S1/SvImJ, A/J, C57BL/6J, BALB/cByJ, DBA/2J | 4 densities; 2 cage types; 3- and 8-mo studies | 12.9 (4, 6); ∼7.6 (7, 10); ∼5.6 (9, 14); ∼4.8 (11, 16) | 83 (4, 6); 49 (7, 10); 36 (9, 14); 31 (11, 16) | 2×; 2.6×; 3× | Growth, blood chemistries, body composition, EKG, blood pressure, aggression, barbering, mortality, organ weights | % Body fat | Higher at higher density (129, A, BALB) | Indicates better metabolic health |
| Kidney weight | Lower at higher density | Indicates reduced chronic stress | ||||||||||
| Heart weight | Lower at higher density | Indicates reduced chronic stress | ||||||||||
| Adrenal weight | Lower at higher density | Indicates reduced chronic stress | ||||||||||
| Paigen et al. (49) | 2016 | Increased density in a hybrid strain | IVC | (C57BL/6J × 129SvImJ)F1 | 4 densities; shoebox cages; 20-mo study; both sexes | 26 (3); 15.6 (5); 9.8 (8); 6.5 (12) | 168 (3); 101 (5); 63 (8); 42 (12) | 0.5×; 0.8×; 1.2×; 1.8× | Growth, blood pressure, body composition, plasma chemistries, organ weights, flow cytometry (spleen) | None | N/A | B6129F1 mice can be housed at near twice the density specified in the Guide with no adverse effects on well-being |
| Van Loo et al. (17) | 2001 | Influence of group and cage size on male aggression | Static | BALB/cAnNCrlBr | 2 densities; 3 group sizes; 2.5-mo study; males | 12.4 (3, 5, 8); 19.4 (3, 5, 8) | 80 (3, 5, 8); 125 (3, 5, 8) | 1.0×; 0.62× | Behavior, food and water consumption, urinary corticosterone, testosterone, organ weights | Agonistic behavior | Higher in larger cages, regardless of density | Male mice fight more with more floor space |
| Food and water consumption | Higher in larger cages, regardless of density | May be due to increased need for metabolic stability | ||||||||||
| Horn et al. (50) | 2012 | Increased housing density; no stratification for mouse weight | Static | C57BL/6NHsd | <10 to >25 g mice housed at 11 density; wean cage; bedding (3 types) change weekly; clean cages weekly or monthly; 2-mo study; both sexes | 5.5 (25) | 35 (25) | 1.0×; 1.5×; 2.2×; 2.7× | Body weight, behavior, food consumption, fecal corticosterone, cage microenvironment, airway histology, mortality | None | N/A | For C57BL/6NHsd, as many as 25 mice can be housed together with no adverse effects on well-being |
| Bailoo et al. (51) | 2018 | Group size and cage type | Static | C57BL/6ByJ, BALB/cByJ | 3 densities; 3 cage types; 13-wk study; both sexes | 7.1 (8); 11.5 (5); 17.5 (3, 8); 25.4 (5); 44.5 (3, 8); 74.4 (5); 124 (3) | 46 (8); 74 (5); ∼113 (3, 8); 164 (5); ∼287 (3, 8); 480 (5); 800 (3) | 1.7×; 1.0×; 0.7×; 0.5×; 0.3×; 0.2×; 0.1× | Growth, food and water intake, fecal glucocorticoid metabolites, open field test, guessing task, home cage behavior | Food and water intake | Higher at lowest density | May be due to increased need for metabolic stability |
1Toth et al. (64).