Laboratory animal ventilation should balance air quality, animal comfort, and energy efficiency to provide cage environments that optimize animal welfare and research efficiency. Conditions that optimize animal welfare automatically tend to improve research efficiency because it is especially important in research to minimize unintended stress factors. Additionally, the laboratory animal ventilation system should provide a healthy and pleasant environment for researchers and animal caregivers.
This work examines the relationship between the air quality in the macro- (room) and micro- (cage) environments in animal facilities. It provides the first systematic study of the ventilation of the macro- and microenvironments simultaneously. It demonstrates only a weak link between the room ventilation and the conditions inside the microisolator cages. Further, it shows that improvements in the room conditions may harm cage ventilation. For example, low level exhausts can produce 27 percent lower CO2 concentrations in cages while raising it to over 70 percent in rooms.
In order to carry out the research, extensive experimental data was collected to provide an accurate basis for the behavior of mice in terms of heat, carbon dioxide, and ammonia production. They are necessary inputs to the computational fluid dynamics (CFD) simulations. In addition to providing specific data for a particular strain of mouse and a type of bedding, this document details measurements and parameters for experimental procedures that can be used for other species as well.
It was also necessary to carry out numerous measurements to calibrate the CFD model of the cage, particularly to evaluate the resistance of the filter material in the lid of the cage as well as to estimate the effects of any leakage where the bonnet top of the cage sits on the bottom of the cage. It was found that a significant amount of air did flow under the lips of the cages in the wind tunnel tests. The CFD model was modified to account for this. Without the experimental data it would have been impossible to carry out the CFD simulations with any confidence that the model of the cage really represented a typical microisolator cage.
There was also some experimental work done to measure airflow in both empty and occupied rooms with racks of cages containing "dummy" mice that provided both heat and CO2 gas. Unfortunately, the low velocities present in the test rooms made accurate measurement very difficult. The comparison between CFD and measurement did not meet our expectations, particularly for the empty room, which was further complicated by temperature variations in an apparently isothermal situation.
While this document does not define a perfect animal facility it does demonstrate how given options can be chosen to influence the room and the cage. The results form a database of performance data for different configurations to which proposed designs can be compared.
The research proved that raising the supply temperature, which lowers the relative humidity, not only reduces ammonia production but provides conditions closer to the thermoneutral zone for mice. Analyzed supply temperatures of about 22 °C (72 °F) were found to result in room temperatures between 24 and 26 °C (75 to 79 °F) with cages around 2 °C (4 °F) higher. While this is within the preferred temperature range for mice, it may prove too warm for scientists.