Microenvironment in Ventilated Animal Cages with Differing Ventilation Rates, Mice Populations, and Frequency of Bedding Changes.

The purpose of the study was to assess the microenvironment in separately ventilated mouse cages at differing ventilation rates, mice populations, and frequency of bedding changes. We monitored intracage temperature, relative humidity, and concentrations of ammonia and carbon dioxide during 3 experiments. First, the effect of ventilation rate on the microenvironment of cages housing adult male mice was evaluated at 30, 40, 60, 80 and 100 air changes/h. For all ventilation rates tested, ammonia concentration was less than 3 ppm, carbon dioxide concentration ranged from 840 to 3,300 ppm, relative humidity ranged from 42 to 65%, and temperature ranged from 23.2 to 25.3 C. Second, we monitored cage microenvironment continually in experiments during which changing of bedding was delayed. Male mice were used in the experiment, and cages were ventilated (60 air changes/h). Cages were allowed to accumulate soiled material for 26 days, during which time ammonia concentration and relative humidity did not exceed 10 ppm and 45%, respectively. Third, we tested ventilation rate and frequency of bedding changes in ventilated cages containing breeding trios (2 females, 1 male) and their pups. Ammonia concentrations remained at 25 ppm or less for 30, 60, and 100 air changes/h when bedding was changed weekly and for 100 air changes/h when bedding was changed every 2 weeks. We concluded that 30 air changes/h was sufficient to maintain a healthful microenvironment in cages that were housing adult male mice in which bedding was changed weekly. When frequency of bedding changes was reduced to every 2 weeks, 60 air changes/h was sufficient for cages housing adult males, but 100 air changes/h was necessary for cages housing breeding trios and pups.