Behavioral observations.

<p>Sexes and cage types are combined, for a total of 24 cages per strain/timeframe/density (2 sexes ×2 cage types ×6 replicates = 24 cages). The value represents the number of cages of the 24 in which the behavior was observed at least once during the entire 3-month or 8-month timeframe. For example, for strain 129, density group 1, whiskering and barbering were observed in 11 of the 24 cages during the 3-month timeframe and in 20 of the 24 cages during the 8-month timeframe. Alopecia was not observed in any of the strain 129 or DBA cages, regardless of density group or timeframe.</p>a<p>For details of floor space for each density group, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090012#pone-0090012-t001" target="_blank">Table 1</a>.</p><p>Behavioral observations did not differ significantly among density groups. Although behavioral observations did differ among strains, all values were within normal ranges.