Volume I - Section I - Introduction 
Page I - 3 
Recommendations for room ventilation rates of 10 to 15 air changes per hour (ILAR, 1996) are an 
attempt to provide adequate ventilation for the room and the cages. This recommendation is 
based on the assumption that adequate ventilation in the macroenvironment provided sufficient 
ventilation to the microenvironment. This may be a reasonable assumption when cages have a 
top of wire rods or mesh. However, several studies have shown that covering cages with filter 
tops provide a protective barrier for rodents and reduced airborne infections/diseases, especially 
neonatal diarrhea, but can result in a significant differences in microenvironmental conditions 
due to changes in air movement caused by the cover. 
1.3 Literature Review 
The following is the conclusion of pertinent research studies and publications on room air 
distribution and the relationship between macro- and microenvironments, ambient temperature 
on growth, behavioral thermoregulatory responses in rats, and moisture production of rats and 
mice. 
This section also includes a review of ammonia and carbon dioxide physiochemical properties 
and their relevance to the current study. 
1.3.1 Literature Search on Macro and Micro Environmental Relationships 
Carolyn K. Reeb, Robert B. Jones, David W. Bearg, Hendrick Bedigian, and Beverly Paigen: 
Impact Of Room Ventilation Rates On Mouse Cage Ventilation And Microenvironment , 1997, 
Contemp. Topics Lab. Anim. Sci., 36:74-79. 
To assess the impact of room ventilation on animal cage microenvironments, intracage 
ventilation rates, temperature, humidity, and concentrations of carbon dioxide and 
ammonia were monitored in non-pressurized, bonnet-topped mouse cages housing four 
C57BL/6J male mice that weighed 26.5 ± 0.4 g. with autoclaved pine shavings as 
bedding. The top, middle, and bottom rows of a mouse rack were monitored at room 
ventilation rates of 0, 5, 10, and 20 air changes per hour (ACH). 
• Ventilation inside the animal cage increased somewhat from 12.8 to 18.9 ACH as the 
room ventilation rate increased from 0 to 20 ACH, but the differences were not 
statistically significant. Most of the increases occurred in cages in the top row nearest 
to the fresh air supply. Cages containing mice had ventilation rates between 10 and 15 
ACH even when room ventilation was reduced to 0 ACH. This ventilation is a result 
of the thermal heat load of the mice. 
• After six days of soiled bedding, intracage ammonia concentration was < 3 ppm at all 
room ventilation rates and was not affected by increasing room ventilation. Although 
