Evaluation of a 16-week Change Cycle for Ventilated Mouse Cages

Abstract

The methods and conditions for housing research mice have been the subject of many discussions and publications in recent years. At our institution, we began to explore these matters with the goal of reducing stress in the animals and yet maintaining an environment that more closely resembled their habitat in the wild and yet was acceptable to researchers and the technicians that cared for the animals. Through a series of small inhouse studies, we derived a method that allowed the animals to stay in their established environment for longer than the standard 1-or 2-wk period. After several empirical studies, we concluded that the mice could stay in the same cage for 16 wk or perhaps even longer. To achieve this outcome, we perfected a method of removing 75% of the existing cage bedding and replacing it with clean bedding every 2 wk. To substantiate the validity of the method, we conducted a major study that evaluated the conditions of the cage, cage environment and the animals for a 16-wk period. In the study, we compared all of these factors in the 16-wk cages to a set of cages that were completely replaced on a 2-wk cycle. The mice in our study appeared to experience decreased stress, and observation also revealed that the 16-wk method was associated with increased pup survival in several colonies. The revised 16-wk method appears to create mouse cage conditions that are no different than the current standard (that is, every 1 or 2 wk) methods of cage changing.

A multicentre study on spontaneous in-cage activity and micro-environmental conditions of IVC housed C57BL/6J mice during consecutive cycles of bi-weekly cage-change

“…In relative terms, the impact of the cage change on in-cage activity was more marked during day time when the animals rest than during lights off when the animals are active. Our findings are in line with others reporting altered behaviours and responses, and disrupted sleep patterns [ 1 , 9 , 45 – 49 , 73 ].…”

“…The interval between subsequent cage changes is the subject of a large body of studies considering different types of housing systems [ 7 – 24 ], housing density [ 7 , 13 , 19 , 20 , 24 – 26 ], strain, age and sex of the animals [ 13 , 14 , 19 , 20 , 24 , 25 , 27 ], and bedding materials used [ 16 , 17 , 23 , 25 , 28 – 31 ]. In several studies, the build-up of ammonia (NH 3 ) during the period between cage changes has been reported as a critical parameter [ 9 , 10 , 13 , 14 , 16 , 17 , 19 – 21 , 23 – 25 , 27 , 28 , 31 – 34 ], because of its potential threat to animal health [ 7 , 9 , 13 , 16 , 20 , 21 , 24 , 25 , 35 – 38 ] (see also Toxicological Review of Ammonia Noncancer Inhalation [CASRN 7664-41-7] Supplemental Information, September 2016).…”

“…different types of individually ventilated caging systems, IVCs) are not consistent except for static microisolators where the reports are in general agreement [ 16 , 17 , 21 , 24 , 33 ]. Some studies report low NH 3 values for IVC systems even with a prolonged cage-change interval of 2, 3 or even 4 weeks, while others observed higher NH 3 values even with weekly changes [ 7 , 9 , 11 , 13 – 17 , 19 , 20 , 22 , 23 , 39 ]. A separate issue is the question of the safe exposure limit for small rodents [ 11 , 13 , 21 , 22 ], and if the commonly adopted human work-place exposure limit is relevant for mice (25 ppm on average across 8h with accepted peak values of 50ppm; see EPAs Toxicological Review of Ammonia Noncancer Inhalation [CASRN 7664-41-7] Supplemental Information, September 2016)?…”

“…We recently published cumulative records of the spontaneous in-cage activity of female C57BL/6J subjected to a weekly cage-change, including the impact of cage-change and other husbandry routines [ 2 ]. Although the cage change results in a decrease of the in-cage load of mould and bacteria, hence NH 3 concentration (ppm), and an increase of soil-free cage floor space [ 43 , 44 ], the animals react with altered behaviours and responses, increased hart rate and mean arterial blood pressure, disrupted sleep patterns, and increased levels of stress hormones [ 1 , 2 , 9 , 45 – 51 ].…”

Assessing Accumulation of Organic Material on Rodent Cage Accessories

“…6 Air quality has also been measured in studies that evaluated rodent cage change frequency. 7,22,29,37,38,40,47,50,56,57 We did not feel that evaluation of air quality would provide a significant benefit to this study because the majority of cage air quality contamination is associated with the bedding and animal waste on the cage floor. In our study, cage bottoms were changed at the intervals recommended by the Guide.…”