The impact of reduced frequency of cage changes on the health of mice housed in ventilated cages

Our purpose in this investigation was to determine if we could reduce cage changing frequency without adversely affecting the health of mice. We house d mice at three different cage changing frequencies: 7, 14, and 21 days, ea ch at three different cage ventilation rates: 30, 60 and 100 air changes pe r hour (ACH), for a total of nine experimental conditions. For each conditi on, we evaluated the health of 12 breeding pairs and 12 breeding trios of C 57BL/6J mice for 7 months. Health was assessed by breeding performance, wea nling weight and growth, plasma corticosterone levels, immune function, and histological examination of selected organs. Over a period of 4 months, we monitored the cage microenvironment for ammonia and carbon dioxide concent rations, relative humidity, and temperature one day prior to changing the c age. The relative humidity, carbon dioxide concentrations, and temperature of the cages at all conditions were within acceptable levels. Ammonia conce ntrations remained below 25 ppm (parts per million) in most cages, but, eve n at higher concentrations, did not adversely affect the health of mice. Fr equency of cage changing had only one significant effect; pup mortality wit h pair matings was greater at the cage changing frequency of 7 days compare d with 14 or 21 days. In addition, pup mortality with pair matings was high er at 30 ACH compared with other ventilation rates. In conclusion, under th e conditions of this study, cage changes once every 14 days and ventilation rates of 60 ACH provide optimum conditions for animal health and practical husbandry.