Individually Ventilated Cages Research Articles

On the importance of health monitoring

Animal welfare and breeding or validity and reproducibility of research data depend on performant health monitoring programmes as integral part of quality assurance. Many recommendations have been published in the past, but it is essential to update recommendations and to adapt them to current developments in laboratory animal research. In this issue three publications are related to animal health and monitoring and therefore underline the importance of issues related to health. The FELASA working party report by Mahler (convenor) and colleagues updated health monitoring recommendations for mice, rats, hamsters, guinea pigs and rabbits in breeding and research facilities. It is a comprehensive report that addresses important points in animal welfare, therefore the integrality of the manuscript including appendices was printed. They address the general design of health monitoring programmes, the choice of agents to be monitored such as viruses, bacteria, parasites and fungi for different lab animal species. They discuss the interpretation of assays and give examples of reports. It is a useful document for those that have to warrant the health of animals and for those that have to care for and handle animals. The second paper by Spangenberg and colleagues addresses the question whether housing conditions in different individually ventilated cages (IVC) affects maternal performance and pup development of different mouse strains. The results indicated that IVC systems might need to be managed differently for mice of different types and/or different physiological status. The physical construction, location of feed hoppers or air inand outlets may influence maternal performance and pup growth. The third paper by Paigen and colleagues investigated whether culling favors a better survival and growth of mouse pups. A variety of physiological and electrocardiographic parameters, as well as growth and mortality were compared in 468 litters with or without culling. Although several parameters showed statistical differences, all values were considered within a normal physiological range. The study demonstrates that culling does not improve health in comparison to unculled litters. In conclusion, the working party report and the two original articles document the importance of health monitoring in the animal house for breeding and research, as well as continued research on recent developments in laboratory animal medicine.

Impaired Fear Extinction as Displayed by Serotonin Transporter Knockout Rats Housed in Open Cages Is Disrupted by IVC Cage Housing

Anxiety disorders are influenced by both environmental and genetic factors. A well-known example for gene x environment interactions in psychiatry is the low activity (s) allelic variant of the serotonin transporter (5-HTT) promoter polymorphism (5-HTTLPR) that in the context of stress increases risk for depression and post-traumatic stress disorder (PTSD). Previously, we observed robust anxiety-related phenotypes, such as an impairment in fear extinction, in 5-HTT knockout (5-HTT−/−) versus wild-type (5-HTT+/+) rats housed in open cages. Recently, housing conditions were changed from open cages to individually ventilated cages (IVC), which are associated with a high ventilation fold and noise. This switch in housing conditions prompted an unplanned 5-HTT gene x environment interaction study in our rats. The current study shows that lifetime stress by means of IVC cage housing abolished genotype differences in fear extinction between 5-HTT−/− and 5-HTT+/+ rats. Although this effect was not attributed specifically to either the 5-HTT+/+ or the 5-HTT−/− genotype, the findings are in agreement with the modulatory role of serotonin in the processing of environmental stimuli. Our findings also underline the possibility that housing conditions confound the interpretation of anxiety-related behaviours in rodents.

The effect of two different Individually Ventilated Cage systems on anxiety-related behaviour and welfare in two strains of laboratory mouse

The environment in which a laboratory animal is housed can significantly influence its behaviour and welfare, acting as a potential confounding factor for those studies in which it is utilised. This study investigated the impact of two Individually Ventilated Cage (IVC) housing systems on anxiety-related behaviour and welfare indicators in two common strains of laboratory mice. Subjects were juvenile female C57BL/6J and BALB/c mice (N=128) housed in groups of four in two different IVC systems for 7weeks. System One had air delivery at the cage ‘cover’ level at 75 ACH (Air Changes/Hour) and System Two had air delivery at the ‘animal’ level at 50 ACH. Mice were assessed twice a week (e.g. bodyweight) or at the end of the study (e.g. anxiety tests). Our results showed significant differences in anxiety-related behaviour between strains and housing systems. Mice in System Two, regardless of strain, defecated more in the Elevated Plus Maze (EPM), spent less time in the open arms of the EPM, and less time in the central zone of the Open Field (OF). Strain differences in anxiety-like behaviour were seen in the increased defecation by BALB/c mice in the OF and EPM and less time spent in the open arms of the EPM compared to C57BL/6J mice. These results suggest that different IVC housing systems can influence mouse behaviour in different ways, with mice of both strains studied exhibiting more anxiety-related behaviour when housed in System Two (air entry at the ‘animal’ level at 50 ACH), which could impact upon experimental data.

Experimental Measurements Research on Internal Micro-Environment of Individually Ventilated Cage System

This paper firstly presents the operation principle of individually ventilated cages (IVC) system. Measurements on micro-environment of IVC system in laboratory animal room at University of South China are conducted to attain the internal environment parameters (Temperature, humidity, air velocity, air cleanliness and noise). Research results show that internal micro-environment parameters basically meet national standards about the barrier environment, but internal air distribution is uneven. In IVC system, air velocities in the edge side are higher than in the middle side, and the maximum air velocity is about 10% larger than the minimum value. Temperature in internal micro-environment depends on indoor temperatures which IVC system located in, and there has a close correlation between air velocity and temperatures. Internal environment evaluation could provide the first-hand research materials for guiding the breeding and management of laboratory animal.

Behavioural consequences of IVC cages on male and female C57BL/6J mice

Recent developments in the technology to breed and house laboratory rodents for medical research has produced individually ventilated cage (IVC) systems. These IVC systems produce a cage environment significantly different to conventional cages. As it is not known in detail whether housing mice in IVCs impacts on their baseline and drug-induced behaviours compared to mice of conventional filter-top cages a comprehensive multi-tiered phenotyping strategy was used to test the behavioural consequences of IVC housing in male and female C57BL/6JArc mice. IVC had anxiety-like effects in the elevated plus maze, which were more pronounced in female mice whereas cognition and locomotion of all test mice were not modified by IVC housing. Mice raised in IVC cage systems were socially more active than mice of filter-top systems. Furthermore, males raised in IVC exhibited an increased sensitivity to the locomotor-stimulating effects of acute MK-801 treatment compared to males in conventional cages. In summary, this is the first study revealing the longer-term effects of IVC housing on social behaviours and the locomotor response to an acute MK-801 challenge. In conclusion, researchers upgrading their holding facilities to IVC housing may encounter a shift in experimental outcomes (e.g. post pharmacological challenges) and the behavioural phenotype of test mice. Furthermore, differences between the housing conditions of breeding facilities and test facilities must carefully be considered. Finally, researchers should clarify in detail the type of housing test animals have been exposed to when publishing experimental animal research data.

The effects of different types of individually ventilated caging systems on growing male mice

Ventilation rate and turnover rate of dry air vary among different types of ventilation systems used with individually ventilated cages (IVCs) and can affect the well-being of rodents housed in these cages. The authors compared the effects of two types of IVC systems, forced-air IVCs and motor-free IVCs, on 4-week-old C57Bl/6J male mice. The mice were acclimatized to the cages for 8 d and then monitored for 87 d. Their body weights, food and water consumption and preferred resting areas were recorded. Mice that were housed in motor-free IVCs had a significantly greater increase in body weight than those housed in forced-air IVCs, despite having similar food consumption. Mice in forced-air IVCs had greater water consumption than mice in motor-free IVCs. In addition, mice in forced-air IVCs were more frequently located in the front halves of their cages, whereas mice in motor-free IVCs were located with similar frequency in the front and back halves of their cages, perhaps because of the higher ventilation rate or the location of the air inlets and outlets in the rear of the cage. These results suggest that body weight, food and water consumption and intracage location of growing male mice are influenced by the type of ventilation system used in the cages in which the mice are housed.

Individually ventilated cages cause chronic low-grade hypoxia impacting mice hematologically and behaviorally

Use of individually ventilated caging (IVC) systems for mouse-based laboratory investigation has dramatically increased. We found that without mice present, intra-cage oxygen concentration was comparable (21%) between IVC housing and ambient environment caging (AEC) that used wire top lids. However, when mice were housed 4-to-a-cage for 1week, intra-cage oxygen dropped to 20.5% in IVC housing as compared to 21% for AEC housing. IVC intra-cage humidity was also elevated relative to AEC housing. Mice raised in IVC housing as compared to mice raised in AEC housing had higher RBC mass, hematocrit and hemoglobin concentrations. They also had elevated platelet counts but lower white blood cell counts. IVC mice, relative to AEC mice, had increased saccharin preference and increased fluid consumption but similar locomotion, food intake, social exploration and novel object recognition when tested in an AEC environment. Taken together, these data indicate that ventilated caging systems can have a 0.5% reduction from ambient oxygen concentration that is coupled to mouse red blood cell indices indicative of chronic exposure to a hypoxia. Importantly, IVC housing can impact behavioral testing for depressive-like behavior.

Effects of housing density on nasal pathology of breeding mice housed in individually ventilated cages

The 2011 edition of the Guide for the Care and Use of Laboratory Animals includes new recommendations for the amount of floor space that should be provided to breeding mice. When pairs or trios of continuously breeding mice are housed in shoebox cages, they may have less than this recommended amount of floor space. High housing densities may adversely affect animal health, for example, by compromising air quality inside the cage. Hence, some institutions are carefully reevaluating the microenvironments of breeding cages. The use of individually ventilated cages (IVCs) to house research mice allows for greater control over the quality of the cage microenvironment. The authors evaluated the microenvironments of shoebox cages in an IVC rack system housing breeding and non-breeding Swiss Webster mice. Ammonia concentrations were significantly higher in cages housing breeding trios with two litters. Histopathologic lesions attributable to inhaled irritants such as ammonia were found in mice housed in breeding pairs and trios. The authors conclude that the microenvironments of cages in an IVC rack system housing breeding pairs and trios may be detrimental to animal health.

Cage-change interval preference in mice

Before animal research facilities began using individually ventilated cage (IVC) systems for mice, cages were often changed one or more times per week. When using IVC systems, however, it is standard practice to change cages only once every 2-3 weeks. When deciding how often to change cages, personnel may consider the cost of labor needed to change the cage, as well as the cage type and bedding type, rather than animal preference or concern for animal well-being. The authors carried out a simple preference test in groups of mice. Mice were allowed to choose between an unsoiled cage and cages that had not been changed for 1 d, 7 d or 14 d. When evaluating where mice positioned their nests and the amount of time mice spent in the various cages, the authors found that the mice preferred the unsoiled cage. Younger mice (<150 d old) showed a stronger preference for the unsoiled cage than did older mice (>150 d old). Further studies are warranted to evaluate mice's preferences for cages changed at different intervals and to determine whether prolonging the interval between cage changes has any negative effects on mice.

Mice prefer draught-free housing

An increasing number of rodents are housed in individually ventilated cage (IVC) systems, as these seem to be very effective for the protection of animals against infections, as well as protecting the staff against allergens. For the IVC systems to be properly ventilated, a huge amount of air has to be blown into the cage, which may cause a draught at animal level inside the cage. The aim of the present study was to evaluate the preferences of mice for differing levels of air speeds and air changes inside the cage. It has been concluded that mice do react to draughts, whereas they do not seem to be affected by a high number of air changes delivered without draught, which underlines the importance of applying draught-free IVC systems for mice.

Charles River altered Schaedler flora (CRASF®) remained stable for four years in a mouse colony housed in individually ventilated cages

As recommendations for specific pathogen-free housing change, mouse facilities need to re-derive their colonies repeatedly in order to eliminate specified bacteria or viruses. This paper describes the establishment of a new mouse facility using as starting point a small colony of CD-1 mice colonized with the Charles River altered Schaedler flora (CRASF) housed in individually ventilated cages (IVCs). The import of new strains was performed exclusively via embryo transfer using CD-1 mice as recipients. The integrity of the CRASF in caecum samples of the original CD-1 colony and of three inbred mouse lines imported into the colony was proven by a quantitative realtime polymerase chain reaction approach. Furthermore, we searched for bacterial contaminants in the gut flora using non-specific 16S rRNA primers. The bacterial sequences found were closely related to but not exclusively sequences of altered Schaedler flora (ASF) members, suggesting that the ASF is heterogeneous rather than restricted to the eight defined bacteria. Moreover, no pathogens were found, neither using the non-specific 16S rRNA primers nor in routine quarterly health monitoring. As one effect of this defined gut flora, interleukin-10 knockout mice are devoid of colitis in our facility. In conclusion, our approach building up a mouse facility using foster mothers and embryo transfer as well as a strict barrier system and IVCs is suitable to maintain a colony free from contaminating bacteria over the long term. CRASF remained stable for seven mouse generations and was efficiently transferred to the imported mouse strains.

Behavioral effects of ventilated micro-environment housing in three inbred mouse strains

Animal facilities aim to combine animal welfare with cost-efficiency and limited care staff requirements, and individually ventilated cage (IVC) systems were developed towards these goals. While IVC have great sanitary advantages both for the animals but also for the care staff, these systems involve potentially deleterious features such as high levels of air renewal, noise, and subtle vibrations of the racks because of the air filtering system used, but also reduce the frequency of stressful cage changes. It is unknown in how far these conditions may influence the animals' behavior. This issue becomes critical as many facilities are switching to IVC systems, possibly complicating replication of data or biasing ongoing studies. We investigated the effects of IVC housing in mice on different behaviors including anxiety, exploration, and learning in males and females of three common and phenotypically distant strains. Results demonstrate robust effects of IVC in multiple behavioral tests with the direction of the effect strongly dependent on strain and sex. These data should serve to alert researchers that a switch to IVC housing during the course of an experiment has the potential to bias results in a serious manner. In addition, behavioral baseline data will have to be re-established once the switch has been completed.

Impact of IVC housing on emotionality and fear learning in male C3HeB/FeJ and C57BL/6J mice

Housing conditions are known to influence laboratory animal behavior. However, it is not known whether housing mice in individually ventilated cages (IVCs) to maintain optimal hygienic conditions alters behavioral baselines established in conventional housing. This issue is important with regard to comparability and reproducibility of data. Therefore, we investigated the impact of IVC housing on emotionality and fear learning in male C3HeB/FeJ (C3H) and C57BL/6J (B6J) mice housed singly either in conventional type II cages with wire bar lids (Conventional), or in IVCs of the same size, but with smooth, untextured lids (IVC classic), thus acoustically attenuated from external stimuli and with limited climbing facilities compared to Conventional. To evaluate the role of climbing, additional mice were kept in IVCs with lids having wire bars ("grid") added to the inner surface (IVC grid). Spontaneous behavior, sensorimotor behavior, and fear learning were measured. IVC housing reduced activity and enhanced anxiety-related behavior in both strains, whereas grooming latency was reduced in B6J only. IVC housing increased Acoustic Startle Response in C3H but not in B6J mice. The "grid" did not compensate for these IVC housing effects. In contrast, B6J mice in IVC grid performed best in fear potentiated startle while B6J mice in IVC classic performed the worst, suggesting that climbing facilities combined with IVC housing facilitate FPS performance in singly-housed B6J males. Our data show that IVC housing can affect behavioral performance and can modulate behavioral parameters in a general and a strain-specific manner, thus having an impact on mouse functional genomics.

Microbiological monitoring of laboratory mice and biocontainment in individually ventilated cages: a field study

Over recent years, the use of individually ventilated cage (IVC) rack systems in laboratory rodent facilities has increased. Since every cage in an IVC rack may be assumed to be a separate microbiological unit, comprehensive microbiological monitoring of animals kept in IVCs has become a challenging task, which may be addressed by the appropriate use of sentinel mice. Traditionally, these sentinels have been exposed to soiled bedding but more recently, the concept of exposure to exhaust air has been considered. The work reported here was aimed firstly at testing the efficiency of a sentinel-based microbiological monitoring programme under field conditions in a quarantine unit and in a multi-user unit with frequent imports of mouse colonies from various sources. Secondly, it was aimed at determining biocontainment of naturally infected mice kept in an IVC rack, which included breeding of the mice. Sentinels were exposed both to soiled bedding and to exhaust air. The mice which were used in the study carried prevalent infectious agents encountered in research animal facilities including mouse hepatitis virus (MHV), mouse parvovirus (MPV), intestinal flagellates and pinworms. Our data indicate that the sentinel-based health monitoring programme allowed rapid detection of MHV, intestinal flagellates and pinworms investigated by a combination of soiled bedding and exhaust air exposure. MHV was also detected by exposure to exhaust air only. The IVC rack used in this study provided biocontainment when infected mice were kept together with non-infected mice in separate cages in the same IVC rack.

Performance evaluation of IVC systems

An expert Working Group was set up in December 2000 to develop recommendations for users and industry on the evaluation of proper function and operation of individually ventilated cage (IVC) systems. The full report of their recommendations is in two parts--'Part 1: Test Instructions' and 'Part 2: Evaluation Criteria'--both of which have been published in full on the Laboratory Animals Ltd website. They can be found at http://www.lal.org.uk/IVC/index.html. Evaluation of and feedback on the recommendations to further refine their use and scientific basis is encouraged. This Summary Report provides a brief overview of the background to the development of the full report and the issues it addresses.

The impact of low levels of carbon dioxide on rats.

The widespread use of individually ventilated cage (IVC) systems today has made the impact of CO(2) on rodents a highly important matter. Leaving cages from these systems without ventilation increases CO(2) concentrations inside the cages, as CO(2) generated from the animals is no longer removed actively. In modern IVC systems the CO(2) levels may reach 3-5% within a very short time, as the cages are very tightly sealed. The aim of the present study was to investigate the effects of 1%, 3%, and 5% CO(2) by studying the preferences of the animals as well as changes in the heart rate and systolic blood pressure as measured by telemetry. The rats avoided the cages, which contained 3% CO(2). In the telemetric study an anaesthetic effect on the rats were seen at 3% as a drop in the heart rate, and at 5% CO(2) a drop in the systolic blood pressure was also seen. The results from the present study could indicate that CO(2) levels of up to 3% do not affect the animals, or at least only to a minor extent, but that if the animals are exposed to CO(2) levels of higher than 3% they are affected directly as seen by changes in physiological parameters and preferences.

Carbon dioxide concentrations in unventilated IVC cages.

The use of individually ventilated cage (IVC) systems has become more common worldwide. The various systems are becoming more and more sealed in order to protect the animals against infections and the staff against allergens; which, however, may lead to problematic CO2 concentrations, if the cages are left unventilated. In this study it is shown that, depending on how tight the cage is and the number of animals housed in each cage, CO2 inside the cage within 2 h will increase to levels of between 2 and 8%.

Elimination of mouse allergens in the working environment: Assessment of individually ventilated cage systems and ventilated cabinets in the containment of mouse allergens

Background: Laboratory animal allergy is an important occupational disease that is preventable by reduction of exposure to mammalian allergens. Objective: The purpose of this investigation was to assess the efficacy of safety equipment in containing mouse urinary protein (MUP)—specifically, individually ventilated cage (IVC) systems and class I–type and class II ventilated cabinets. Methods: Six IVC systems (which are used to house rodents) were operated at positive and negative pressure. Air samples (2 L/min) were collected at the cage front, cage back, air inlet, and air outlet, and the MUP was quantified by immunoassay. The background MUP of the IVC study room was compared with that of rooms where mice were housed conventionally or in isolators. Class I–type cabinets (n = 2) were tested during the disposal of soiled litter. Air samples were positioned on and behind the operator and inside the cabinet (n = 2). Personal samples were collected while scientific procedures were performed in a class II cabinet and in the open. Results: All of the IVC systems contained MUP effectively (>250-fold) when operated at negative pressure. At positive pressure, the “unsealed” IVC racks leaked MUP (1- to 25-fold reduction) but the “sealed” IVC system did not. Class I–type cabinets reduced (10-fold) but did not eliminate exposure during “cleaning out.” No MUP was detected when procedures were performed in class II cabinets (protection factor, >10-fold). Conclusion: Safety equipment can substantially reduce exposure to mouse allergen. Allergen exposure in holding rooms will be minimized if mice are housed in IVC systems operated at negative pressure or in “sealed” IVC systems at positive pressure. Respiratory protection should be used whenever “unsealed” IVC systems are operated at positive pressure or during “cleaning out” in class I–type cabinets. (J Allergy Clin Immunol 2001;108:288-94.)