Floor Space Needs for Laboratory Mice: C57BL/6 Males in Solid-bottom Cages with Bedding

Measures of performance, mortality, adrenal weights, plasma glucocorticoid concentration, and selected immune measures were collected in an attempt to define space needs of laboratory mice. Six replications of 3 C57BL/6 male mice per cage were examined while housed on bedding at 5, 10, 15, or 20 in(2) (32.2, 64.5, 96.8, or 129 cm(2)) per mouse. Body weights were not influenced by treatment; however, mice in smaller spaces (5 in(2) per mouse) consumed or wasted more feed and water than mice given greater space allowances. Mice given the least amount of space (5 in(2) per mouse) had greater lymphocyte proliferation in response to the T-cell mitogen PHA than mice given more space. Mice provided 10 in(2) per mouse had greater natural killer cytotoxicity than mice given greater or less space. Mouse mortality was greater as more space was provided. In contrast, adrenal weights and plasma glucocorticoid concentrations were progressively greater with lower space allowances. The National Research Council 1996 recommendation of 15 in(2) per mouse, for this strain and sex of mice, would result in greater mortality and reduced activity of some immune measures. Socially housed male C57BL/6 mice will benefit from less space than recommended by the National Research Council in 1996.