Volume I - Section I - Introduction 
Page I - 19 
Louis J. Serrano: Carbon Dioxide and Ammonia in Mouse Cages: Effect of Cage Covers, 
Population, and Activity, 1971, Lab. Anim. Sci., 21:75-85. 
To determine the affect of rod, wire-mesh, and fibrous filter types of covers on diffusion 
or convection of gases produced in the cage, groups of 4, 8, or 16 mice were placed in 
cages. Samples of air from each cage were analyzed daily. Filter and mesh covers had a 
major influence on the composition of air in the cages. They allowed the accumulation of 
CO2, NH3, and probably other gases to rise to levels considerably higher than in cages 
with open covers. When the mice were active, or when the number of mice in the cage 
was doubled, the CO2 level was increased 50 to 100 percent above the original level of 
each cage. NH3 was not detected until the 3rd to 6th day (3rd day for 16 mice per cage 
and to 6th day for 4 mice per cage), depending on the number of mice per cage. By the 
7th day air reached noxious levels under some covers. Limiting the number of mice per 
cage and frequently removing soiled bedding could prevent excessive levels of CCL and 
NH3 from accumulating in protectively covered cages. 
• Significance of ammonia levels: Ammonia was not detected until the 5th or 6th day in 
a protectively covered cages holding no more mice than the number recommended for 
its size. 
• Carbon dioxide is a metabolic by product of respiration and its accumulation is 
influenced by activity level of the animals, population density, and airflow within the 
cage. CO2 levels were significantly higher in all cages than in the room. The levels in 
protective cover cages were in the range of 1217 parts per million for 4 mice per cage 
to 3155 parts per million for 16 mice per cage. 
T.R. Schoeb, M.K. Davidson, and J.R. Lindsey: Intracage Ammonia Promotes Growth of 
Mycoplasma Pulmonis in the Respiratory Tract of Rats, 1982; J.R Broderson, J.R. Lindsey, J.E. 
Crawford: The Role of Environmental Ammonia in Respiratory Mycoplasmosis of Rats, 1976, 
Am. J. Path., 85:115-130. 
Ammonia concentrations >25 ppm promote the growth of infective agents in the 
respiratory tracts of rats. 
M.L. Simmons, D.M. Robie, J.B. Jones, and L.J. Serrano: Effect of a Filter Cover on 
Temperature and Humidity in a Mouse Cage, 1968, Lab. Anim., 2: 1 13-120. 
To determine how a filter cap affects the heat and moisture buildup in a mouse cage and 
how that buildup is affected by ambient conditions of temperature and relative humidity, 
50 adult female mice were housed 10 per cage in polycarbonate cages that were covered 
with a fibrous filter and sealed with a neoprene gasket and hold-down rod. The cages 
were placed in a chamber that controlled ambient temperature and humidity. 
Observations were made at 1 °F intervals of temperature 68 to 74 °F and at three different 
