The use of dirty bedding for detection of murine pathogens in sentinel mice

Sentinel Swiss (CD-1) mice, housed without filter bonnets, were seronegative for mouse hepatitis virus (MHV) for 8 consecutive months in an experimental colony of CD-1 mice. MHV titers had been detected sporadically in sentinel mice housed in this colony during a 2 year period. In an effort to determine whether MHV was still present in the colony, two methods of exposing sentinel mice to an animal room environment were compared under routine husbandry practices. Eight cages (12 mice per cage; 2 cages per rack) of experimental virus antibody free sentinel mice, housed without filter bonnets, were placed on the bottom shelf of 4 of 12 racks in the room. Twice each week, four cages of sentinel mice received a composite sample of dirty bedding (bedding used previously by mice in the room). The remaining four cages of experimental sentinels received fresh non-used bedding. Sentinel mice were bled at monthly intervals for MHV serology. After 4 months, mice from two cages which received dirty bedding seroconverted to MHV and mice from one cage were positive for Myobia musculi (mites). Three weeks later, all four cages of mice which received dirty bedding were positive for MHV and three were positive for mites. In contrast, only two of four cages of mice which received fresh bedding were positive for MHV and all were negative for mites. These findings indicate the importance of exposing sentinel mice to dirty bedding and that MHV and mites may go undetected for several months in a mouse colony when the incidence levels are low where standard sanitation procedures are used.     

Effects of cage beddings on microsomal oxidative enzymes in rat liver

The purpose of the present studies was to evaluate the effects of some commercially available cage beddings on rat liver microsomal cytochrome P-450-dependent drug-metabolizing enzyme, ethylmorphine N-demethylase, and the carcinogen-metabolizing enzyme, benzo(a)pyrene hydroxylase. Sprague-Dawley rats were housed in cages containing cedar chip, corncob or heat-treated pinewood bedding for 3 weeks. Control rats were housed in cages on wire bottom floors containing no bedding material. Rats housed in cages containing cedar chip showed 18, 46 and 49% increases in liver cytochrome P-450 content, ethylmorphine N-demethylase and benzo(a)pyrene hydroxylase activities, respectively. The liver enzyme activities of rats housed in cages containing corncob bedding were similar to those obtained with control rats. In contrast, the pinewood-bedded rats showed a 21% decrease in ethylmorphine N-demethylase activity without affecting cytochrome P-450 content and benzo(a)pyrene hydroxylase activity. Hexobarbital-induced sleep times of the variously bedded rats were similar to those of control animals. These data suggest that the commercial bedding materials differ in their abilities to affect liver microsomal enzymes. Thus, interlaboratory variability in basal enzyme activities reported in the literature may be partly due to bedding materials used in the animal's cages.     

Urologic syndrome associated with wire caging in AKR mice

Individually housed male AKR/NCrlBR mice used in a chronic inhalation experiment were noted to develop a severe obstructive genitourinary condition. The mouse urologic syndrome (MUS) had one or more of the following features: bladder distension; peripreputial urine staining, alopecia, and edema; paraphimosis; urethral blockage; ulcerative balanophosthitis; hydronephrosis; pyelonephritis; rectal prolapse; and perineal ulcerative dermatitis. MUS was less severe and less prevalent in similarly housed B6C3F1/CrlBR and NIH-Swiss mice used in the same experiment. Epidemiologic evidence within the animal facility restricted the syndrome to the inhalation toxicology area. The effects of intermittent water deprivation as well as wire caging on the development of MUS were studied because these conditions were only utilized in the inhalation facility. Male AKR/NCrlBR mice, caged individually in suspended wire caging or kept isolated in polystyrene shoebox style cages containing wire floorwalk bottoms, all developed MUS within 16 weeks. Mice which were housed directly on hardwood bedding in identical plastic caging remained free of the syndrome, as did castrated males which were kept in suspended wire cages. Water deprivation was not found to be a major contributing factor to the development of the condition, but was found to augment its severity. We concluded that although MUS is probably multifactorial in etiology, housing susceptible animals on wire bottom caging may exacerbate the incidence and severity of the condition in certain strains of male mice.     

Effect of cage bedding on temperature regulation and metabolism of group-housed female mice

Mice are generally housed in groups in cages lined with an absorbent bedding material at ambient temperature (Ta) of 20 to 24 degrees C, which is comfortable for humans, but cool for mice. Little is known about the effects of bedding on thermoregulation of group-housed mice. To determine whether bedding material affects thermoregulatory stability, core temperature (Tc) and motor activity (MA) were monitored by use of radiotelemetry in female CD-1 mice housed in groups of four in a standard plastic cage at Ta of 23.5 degrees C. Ten groups were tested using three types of bedding material: a deep layer of heat-treated wood shavings (DWS) that allowed mice to burrow, a thin layer of wood shavings (TWS) just covering the bottom of the cage floor, or a layer of beta chips (BC). Mice could not burrow in the TWS or BC. The Tc and MA were affected by bedding type and time of day. Mice housed with DWS maintained a significantly higher Tc (deltaTc = 1.0 degrees C) during the day, compared with that in mice housed with TWS and BC. During the night, Tc and MA were high in all groups and there was no effect of bedding type on Tc or MA. Effect of bedding on metabolic rate (MR) was estimated by measuring oxygen consumption for six hours in groups of four mice at Ta of 23.5 degrees C. The Tc was significantly reduced in mice housed on the TWS and BC, but MR was unaffected by bedding type. There was a trend for higher MR in mice on BC. Compared with use of other bedding materials, housing mice on DWS and comparable materials provides an environment to burrow, thus reducing heat loss. The effects of bedding material on temperature regulation may affect rodent health and well being. Moreover, bedding will affect variability in toxicologic and pharmacologic studies whenever an endpoint is dependent on body temperature.     

Reliability of soiled bedding transfer for detection of mouse parvovirus and mouse hepatitis virus

Serologic monitoring of sentinel mice exposed to soiled bedding is a common method of detecting viral infections in mice. Because bedding transfer protocols vary, the sensitivity of this method has not been documented sufficiently. We examined the reliability of bedding transfer during various stages of infection with mouse parvovirus (MPV) and mouse hepatitis virus (MHV). Most mice exposed to bedding contaminated with MPV 0, 3, or 7 d previously seroconverted, whereas only mice exposed to bedding contaminated with MHV 4 h previously seroconverted, thus confirming the differing stabilities of these viruses. Index mice were inoculated with 30 times the infectious dose 50 (ID50) of MPV or 300 ID50 of MHV. At 3 d, 1 wk, and 2 wk postinoculation (PI), we transferred 25, 50, or 100 ml of bedding to cages of sentinel mice. Viral infection and shedding by index mice was confirmed by serology and fecal polymerase chain reaction assay. Transfer of soiled bedding between mice in static cages induced seroconversion of sentinel mice most reliably during peak viral shedding (1 wk PI for MPV and 3 d PI for MHV). Soiled bedding transfer between mice in individually ventilated cages induced a higher prevalence of sentinel seroconversion to MPV and MHV than that after transfer between mice in static cages. Our findings indicate that although soiled bedding transfer is an effective method for detecting MHV and MPV under optimal conditions, the method is less than 100% reliable under many conditions in contemporary mouse facilities.     

The effectiveness of a microisolator cage system and sentinel mice for controlling and detecting MHV and Sendai virus infections

Experiments were conducted to determine (a) whether BALB/c mice housed on soiled bedding can be used as sentinels for the detection of Sendai virus and MHV from infected mice housed in microisolators, and (b) whether the microisolator caging system protects mice against Sendai virus and MHV infections. Sentinel mice were housed in microisolator cages, exposed continuously to soiled bedding and bled at 21 and 42 days for serology. All sentinel mice were seropositive for MHV by 42 days; however, sentinel mice exposed to soiled bedding were seronegative for Sendai virus at 21 and 42 days. These results suggest that sentinels housed on soiled bedding may not detect all infectious murine viruses. This study also showed that the microisolator caging system provided an effective barrier against MHV infection at the cage level and suggests that the microisolators should protect mice against other infectious agents.     

Mate Choice for Non-siblings in Wild House Mice: Evidence from a Choice Test and a Reproductive Test

Two experiments were designed to test whether wild house mice discriminate between olfactory cues from different kin and, if so, whether given preferences would relate to actual reproductive decisions. Experimental animals were mice born to the offspring of wild-caught house mice. Litter-mates stayed together until 60 d of age and were then housed individually. In a choice test, animals were placed in the middle of an arena with 4 openings which led to small cages containing bedding material from opposite-sex animals of known kinship (full-sib, cousin, unrelated) or clean material. Test animals (11 oestrous females, 11 males tested with oestrous females' bedding, 8 males tested with material from non-oestrous females) preferred conspecific to control bedding. Males tested with oestrous females' bedding significantly preferred unrelated to full-sib odours. In a second experiment, 34 males were each mated simultaneously to 3 females (sister, cousin, unrelated) and these groups were then housed together for 5, 10, and 15 d. Females were checked for litters during the next 20 d. Reproductive rate increased significantly in the 15 d cohabitation group, and significantly more cousin and unrelated females than sisters gave birth to a litter.     

Social cues influence growth and sexual maturation of the male musk shrew (Suncus murinus)

Musk shrews were maintained from weaning (20 days of age) for 20 or 40 days in one of several social conditions. In Exp. 1, young males housed with adult females gained more weight and had heavier sex accessory organs than did young males housed with an adult male or reared alone. In Exp. 2 this same pattern of accelerated growth and sexual maturation was found when males were reared directly with an adult female or in a split cage where a wire barrier served to separate the male and his adult female cagemate. In Exp. 3, males were reared in cages containing clean or soiled bedding: soiled bedding was taken once every 5 days from the cage of an adult male, or a female. Under these conditions differences in the weights of reproductive tissues showed minimal variation with housing condition after 20 days of treatment. At that time males reared in soiled bedding taken from the cage of an adult female had accelerated development compared with control males. In Exp. 4, males were housed alone or in a split cage with an adult female which was separated by a wire mesh or a solid, opaque barrier. Males separated by a solid barrier from their female cagemates for 40 days had reproductive tissue weights equivalent to those measured in males reared alone. Taken together these results suggest that the presence of an adult female has dramatic effects on body growth and development of reproductive target tissues in young male musk shrews. Male-female social interactions could play an important role in the timing of puberty in this opportunistically breeding tropical mammal.     

Maintenance of mice in automatic rearing system. I. Rearing tests with ICR mice (author's transl)

Female ICR:JCL mice were reared in wire-mesh cages with nozzles for automatic water supply on a battery with an automatic washing system, and the evaluation of this system was made in comparison with the conventional feeding system with water bottles, alumite cages and changes of the bedding. In weight gains, feed intakes, water consumption, leucocyte and erythrocyte counts, hematocrit values or vaious organ weights during the period from 3 to 14 weeks of age, animals maintained by the automatic rearing system showed no significant difference as compared with those maintained by the conventional system, providing evidence for a conspicuous labor saving with the automatic control system.     

Preferences of group-housed female mice regarding structure of softwood bedding

Bedding influences various parameters in the housing of laboratory mice, such as health, physiology and behaviour (often considered as being integral parts of welfare). Notwithstanding existent studies about bedding preferences of individually tested mice, data about group-housed mice are still lacking. The aim of this study was to find out the structure preference for softwood bedding of group-housed mice. One hundred and eight 8-week-old female mice (C57BL6/JOlaHsd and BALB/cOlaHsd) were housed in groups of three and were given one-week free access to two different bedding structures at a time. In three test combinations, softwood shaving bedding was tested versus softwood chip bedding products of three different particle sizes (fine/medium/coarse-grained). The preference test was performed in a DoubleCage system composed of two Makrolon type IIL cages, connected by a perspex tunnel. This validated system was able to detect the crossings of each individual animal with correct crossing time and direction. On the basis of these data, dwelling times on the particular bedding structures were statistically analysed as a parameter for bedding preferences. In all three test combinations, a highly significant shaving preference was detected. On average, mice spent 70% of their dwelling time on the shavings. This preference was more explicit during the light period and in C57BL/6J mice. The relative ranking of the bedding structures was: shavings > coarse-grained chips > medium chips = fine chips. By means of these results, a shaving structure as bedding can be recommended for laboratory mice, whereas fine chip structures should be avoided.     

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.     

Intermittent stimulation and delay of puberty by urinary chemosignals and social contact in wild stock female house mice (Mus Domesticus)

A sequence of six experiments using wild stock house mouse (Mus domesticus) tested the effects of intermittent stimulation with either the urinary chemosignal released by grouped female mice or social contact from grouped females on the age of first vaginal oestrus in young females. Weanling female mice were exposed to bedding soiled by grouped females or cages containing grouped females for 15 min periods, then removed for a prescribed period, and placed again in a cage with soiled bedding or grouped females. The nature of the exposure to the puberty delaying effect, the number of total exposures each day, the total length of exposure to the stimulus, and the total time period over which the exposures occurred were varied. None of the treatment regimes employed here with soiled bedding from grouped females resulted in delays in the onset of first oestrus in test females. Young females exposed to grouped females for 6 or 8 exposures in a 4 h period, 6 or 8 exposures in an 8 h period, or 8 exposures in a 12 h period were significantly delayed in attaining puberty relative to control females that were exposed to cages containing clean bedding. These results are in contrast to earlier findings involving chemosignals that accelerate first oestrus wherein young females exhibited the capacity to accumulate the exposures to the urinary chemosignals from males, females in oestrus and pregnant or lactating females. Direct exposure to the grouped females on an intermittent basis can provide stimulation that is cummulative and results in delays in the onset of first oestrus.     

Role of photoperiod and temperature in production of the oestrus-inducing pheromone in male wild mice

Ninety adult males divided in six equal groups were exposed to different photoperiods for 21 days. Exposures included natural light (ca 11 hr), long photoperiod (16L:8D) and short photoperiod (8L:16D). The first three groups received these exposures at room temperature (13-20 degrees C) while the remaining three at raised temperature (36-38 degrees C). Soiled bedding of the above males was introduced in the cages of unisexually housed noncyclic females and their potentiality to induce oestrus was assessed. It was noticed that the bedding of all the males proved to be a stimulus inducing oestrus in the majority of the females during the 7 day exposure. There was no significant difference in the number of females returning to oestrus following exposure to soiled bedding of different males. These results elucidate that environmental factors, especially light and temperature do not influence the production/release of the oestrus-inducing pheromone in wild mice.     

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.     

Social influences on reproductive development and fertility in female Djungarian hamsters (Phodopus campbelli).

Social influences on the sexual maturation of female Djungarian hamsters were investigated in two experiments. In the first experiment females were housed from weaning with an adult male, by themselves, or with a weanling sister. Maturation was accelerated in females housed with males as indicated by younger age at first ovulation, increased rates of ovarian and uterine growth, and lower LH levels at some ages. Maturation was delayed in females housed with sisters compared to those housed alone as measured by time of first ovulation and by lower estradiol levels at some ages. The most marked differences between groups occurred 8 to 12 days after weaning, suggesting that events during this period are particularly important in the social mediation of sexual maturation. In the second experiment the effects of reproductive suppression (caused by living with a sister) on the subsequent fertility of females housed with males were examined. If male-female pairs were housed in clean cages, no effects were observed; however, pairs housed in cages previously soiled by the female and her sister had fewer young surviving until 1 week of age despite no differences in the age of pregnancy onset or in the initial litter size. Thus, even cues present in unrenewed soiled bedding may have subtle but long lasting effects on reproductive function.     

Effects of Different Types of Bedding Materials on Behavioral Development in Laboratory CD1 Mice (Mus musculus)

Male and female mice were housed in cages, containing different types of bedding materials (wood flakes or pulp chips), from 4 weeks of age in the F₀ generation to 11 weeks of age in the F₁ generation; selected reproductive and neurobehavioral parameters were measured in the F₁ generation. There were no adverse effects of bedding materials on litter size, litter weight, or sex ratios at the time of birth. With regard to behavioral development parameters, bedding materials did not influence any variables (p > 0.05) in both sexes. Regarding exploratory behavior in the F₁ generation, number of defecations significantly varied (p = 0.0203) with bedding materials in males at 3 weeks of age. The number of horizontal activities also significantly varied (p = 0.0342) with bedding materials in males at 8 weeks of age. Multiple‐T water maze performance data indicated that the time required was significantly shortened across trials in pulp chips group than wood flakes group in males (p = 0.0211). Moreover, all spontaneous behavior variables in males significantly varied with bedding materials, particularly the average time of movement was significantly different (p = 0.0037) in distance between parallel lines of types of bedding materials in the F₁ generation. The present study shows that bedding materials influence the neurobehavioral development in mice     

Efficacy of three microbiological monitoring methods in a ventilated cage rack

The use of individually ventilated caging (IVC) to house mice presents new challenges for effective microbiological monitoring. Methods that exploit the characteristics of IVC have been developed, but to the authors' knowledge, their efficacy has not been systematically investigated. Air exhausted from the IVC rack can be monitored, using sentinels housed in cages that receive rack exhaust air as their supply air, or using filters placed on the exhaust air port. To aid laboratory animal personnel in making informed decisions about effective methods for microbiological monitoring of mice in IVC, the efficacy of air monitoring methods was compared with that of contact and soiled bedding sentinel monitoring. Mice were infected with mouse hepatitis virus (MHV), mouse parvovirus (MPV), murine rotavirus (agent of epizootic diarrhea of mice [EDIM]), Sendai virus (SV), or Helicobacter spp. All agents were detected using contact sentinels. Mouse hepatitis virus was effectively detected in air and soiled bedding sentinels, and SV was detected in air sentinels only. Mouse parvovirus and Helicobacter spp. were transmitted in soiled bedding, but the efficacy of transfer was dependent on the frequency and dilution of soiled bedding transferred. Results were similar when the IVC rack was operated under positive or negative air pressure. Filters were more effective at detecting MHV and SV than they were at detecting MPV. Exposure of sentinels or filters to exhaust air was effective at detecting several infectious agents, and use of these methods could increase the efficacy of microbiological monitoring programs, especially if used with soiled bedding sentinels. In contemporary mouse colonies, a multi-faceted approach to microbiological monitoring is recommended.     

Effects of water dilution, housing, and food on rat urine collected from the metabolism cage

The objective of the study reported here was to investigate three factors that may affect the amounts of water consumed and urine excreted by a rat in the metabolism cage: water dilution, housing, and food. Young F344/N rats (eight per group) were used for all experiments. Food was withheld from rats before each 16-h urine collection, then rats were transferred into a metabolism cage. For trial A (water dilution), urine was collected from rats supplied with dyed water (0.05%, vol/vol). This was repeated three times over a 2-week period. Dye in water or urine was quantified, using a spectrophotometer. For trial B (housing), rats were individually housed in wire cages for 3 weeks before the first urine collection. Then they were group housed in the solid-bottom cage (four per cage). After 2 weeks of acclimation, urine collection was repeated. For trial C (food), one group of rats was provided with food, the other was not, during urine collection. About 8% of urine samples of small volume (< or = 3 ml) from trial A were contaminated with drinking water up to 13% of volume. The average urine volume associated with individual housing was approximately twice as large as that associated with group housing. When food was provided during urine collection, rats consumed similar amounts of water but excreted significantly smaller amounts of urine than did rats without food. It was concluded that water dilution of a urine sample from a sipper bottle is relatively small; rats individually housed in wire caging before urine collection can consume and excrete a larger quantity of water, compared with rats group housed in solid-bottom cages; and highly variable urine volumes are, in part, associated with lack of access to food during urine collection.     

笼底类型对肉仔鸡行为的影响及其与胸囊肿发生率的关系

为研究笼养肉仔鸡胸囊肿发生的行为学机制,观察比较3种盒式笼(笼底分别由铁丝网、塑料片和竹竿组成)中肉仔鸡从3至6周龄的行为,以及胸囊肿发生率的差异。结果表明6周龄时,肉仔鸡在3种笼底上的伏卧行为虽无显著差异,但在行为格局中其比例最高(均在70%以上),而站立、行走和晃动3种行为之和仅占10%左右;竹竿笼底上的肉仔鸡行走频次、晃动频次和比例均显著高于铁丝和塑料笼底上的(均P<0.05),而竹竿笼底上的肉仔鸡胸囊肿发生率显著低于铁丝笼底上的(P<0.05);随着周龄增长,铁丝笼中肉仔鸡行走和晃动频次均减少,伏卧时间延长,胸骨承受的重量增大,这增加了胸部与铁丝网笼底接触及摩擦的几率和时间。实验结果说明,笼养肉仔鸡行为格局趋向静态单一化(动态行为频次降低,静态行为比例占优势)与其胸囊肿发病率的变化相一致,提示两者存在某种内在联系。这验证了我们提出的假设,即依赖于笼底类型和周龄的肉仔鸡行为趋向静态性是胸囊肿形成的必经环节。     

The influence of bedding depth on behaviour in golden hamsters (Mesocricetus auratus)

Although digging was found to be important in captive rodents, most golden hamsters are provided with only little material to dig. In this study, the influence of different bedding depths and acute stressors on the behaviour and welfare of golden hamsters was analysed. Forty-five male golden hamsters were assigned singly to three experimental groups with 80, 40 or 10 cm deep wood shavings. Behaviour was evaluated by continuous running wheel activity and video recordings, a series of stressors was applied after 7 and 8 weeks. Burrows, if constructed, were mapped monthly. Additionally, adrenals, testes and body mass as well as hormone levels of corticosteroids and testosterone were measured at euthanasia. Hamsters kept with 10 cm deep bedding showed significantly more wire-gnawing and a higher running wheel activity than the hamsters in the other groups. In 80 cm deep bedding wire-gnawing was never observed. Stressor application showed no significant immediate influence on behaviour. All hamsters in 40 and 80 cm bedding constructed burrows which they occupied. The body condition (body weight/body size³) was significantly higher in the animals kept in deep (80 cm) compared with those housed in low (10 cm) bedding cages. The relative testes weights were significantly heaviest in the medium treatment group. No significant differences could be detected for the adrenal glands and testosterone levels. In this study, we showed that cages with at least 40 cm of bedding seemed to enhance the welfare of golden hamsters, although those in 80 cm bedding had more body fat compared with the other groups. However, deep bedding which is appropriate for burrowing can be recommended for golden hamsters.