Effects of cage density on behavior in young adult mice

Optimal housing conditions for mice can be achieved by minimizing environmental variables, such as those that may contribute to anxiety-like behavior. This study evaluated the effects of cage size on juvenile mice through assessment of differences in weaning weight, locomotor skills, and anxiety-like behavior. Eighteen pairs of male and pregnant female Swiss-Webster (Cr:SW) mice were housed in 3 different caging scenarios, providing 429, 505, or 729 cm2 of space. Litters were standardized to 10 pups per litter in each cage. Mice reared in each caging scenario were assessed with the open-field, light-dark exploration, and elevated plus-maze tests. No differences in weaning weight were noted. Mice reared in the 505- and 729-cm2 cages explored a significantly larger area of the open-field arena than did those in the 429-cm2 cages. Those reared in the 505-cm2 cages spent more time in the center of the open field than did those in the 729-cm2 cages, suggesting that anxiety-like behavior may be increased in the animals housed in the larger cages. This study did not establish a consistent link between decreased floor space and increased anxiety-like behavior; neither does there appear to be a consistent effect of available floor area on the development of locomotor skills on mouse pups.     

Behavioral assessment of intermittent wheel running and individual housing in mice in the laboratory

Physical cage enrichment—exercise devices for rodents in the laboratory—often includes running wheels. This study compared responses of mice in enriched physical and social conditions and in standard social conditions to wheel running, individual housing, and open-field test. The study divided into 6 groups, 48 female BALB/c mice group housed in enriched and standard conditions. On alternate days, the study exposed 2 groups to individual running wheel cages. It intermittently separated from their cage mates and housed individually 2 groups with no running wheels; 2 control groups remained in enriched or standard condition cages. There were no significant differences between enriched and standard group housed mice in alternate days' wheel running. Over time, enriched, group housed mice ran less. Both groups responded similarly to individual housing. In open-field test, mice exposed to individual housing without running wheel moved more and faster than wheel running and home cage control mice. They have lower body weights than group housed and wheel running mice. Intermittent withdrawal of individual housing affects the animals more than other commodities. Wheel running normalizes some effects of intermittent separation from the enriched, social home cage.     

Training Nonhuman Primates Using Positive Reinforcement Techniques

Physical cage enrichment—exercise devices for rodents in the laboratory—often includes running wheels. This study compared responses of mice in enriched physical and social conditions and in standard social conditions to wheel running, individual housing, and open-field test. The study divided into 6 groups, 48 female BALB/c mice group housed in enriched and standard conditions. On alternate days, the study exposed 2 groups to individual running wheel cages. It intermittently separated from their cage mates and housed individually 2 groups with no running wheels; 2 control groups remained in enriched or standard condition cages. There were no significant differences between enriched and standard group housed mice in alternate days' wheel running. Over time, enriched, group housed mice ran less. Both groups responded similarly to individual housing. In open-field test, mice exposed to individual housing without running wheel moved more and faster than wheel running and home cage control mice. They have lower body weights than group housed and wheel running mice. Intermittent withdrawal of individual housing affects the animals more than other commodities. Wheel running normalizes some effects of intermittent separation from the enriched, social home cage.     

The effects of parity, litter size, season, and breeding protocol on the number of DBA/2J Ten mice available for weaning.

Data on the reproductive behavior of DBA/2J Ten mice, collected from October 1970 through March 1973 and utilizing a 2-female, 1-male breeding system, with the mice remaining together throughout their reproductive life indicates: a) Litter size tends to increase through the fourth litter, the first litter being much smaller than successive litters; b) Survival rates of litters with 2--4 pups increase with successive deliveries; c) Survival rates of litters with 5--9 pups are approximately the same regardless of parity; d) There is a circannual rhythm in the number of pups available for weaning da 21, which is attributable to changes in postnatal viability. Data collected using a breeding pen system, with isolation of females pre- and post-delivery (March 1973 to March 1974) indicates: a) There is a reduction in live litter sizes in later litters with this system; b) There is a large reduction in the proportion of pups surviving to weaning with this system when compared with the other breeding system.     

The domestication of Crocidura dsinezumi as a new laboratory animal.

The dsinezumi shrew (Crocidura dsinezumi), a small insectivore, has been bred for the first time as a laboratory animal. The original animals were captured using Sherman's live traps and transferred into wooden cages. After several generations they were housed in plastic cages. Their diet consisted of trout pellets, cat food, and water provided ad libitum. Monogamous pairs were housed together for 2-3 weeks for mating, and the male was separated from the female during delivery and nursing. In captivity, the reproductive activity was observed throughout the year and the gestation period was estimated at 28-30 days with a litter size of between 1 and 4 pups. Pups grew very rapidly, and reached adult body size (mean: male, 9.7 g; female, 8.3 g) and sexual maturation at 6-8 weeks of age. The reproductive life was estimated at one and a half years, while the longevity was approximately 2 years.     

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.     

The Effect of Cage Space on Behavior and Reproduction in Crl:CD1(Icr) and C57BL/6NCrl Laboratory Mice

Recommendations for the amount of cage space required for female mice with litters were first made in the 2011 Guide for the Care and Use of Laboratory Animals. We hypothesized that if a difference in mouse behavior and reproduction exists within the limits of commercially available caging, this difference would be detected between the smallest and largest cages. C57BL/6NCrl and Crl:CD1(Icr) breeding mice were randomly assigned to a cage treatment: LP 18790 (226cm²); A RC1 (305cm²); A N10 (432cm²); T 1291 (800cm²) and a breeding configuration: single (male removed after birth); pair (1 male + 1 female); or trio (1 male + 2 females) in a factorial design for 12 weeks. All cages received 8-10g of nesting material and nests were scored weekly. Pups were weaned between post-natal day 18 and 26 and were weighed at weaning. Adult behavior and location in the cage were recorded by scan samples every 30 min over 48 hr of video recorded on PND 0-8 and PND 14-21 when pups were in the cage. Press posture and play behavior were recorded by 1/0 sampling method. Cage space did not significantly alter typical reproductive measures. Pups in the smallest cage played less than in the other cages. Adults in the smallest cage displayed more press posture than in the two largest cages. Mice in the largest cage spent more time under the feeder than in other areas of the cage. Nest score was also the highest in the largest cage. Housing breeding groups of mice in a range of commercially available cage sizes does not affect reproduction but behavioral measures suggest that the smallest cage tested, LP 18790, may be stressful for outbred mice when pups are present.     

Maternal behavior deficits in nulliparous oxytocin knockout mice

The first observations of postpartum oxytocin knockout (OTKO) mice found no maternal behavior deficits. However, it is unclear how detailed those observations were. In this study, we compared maternal behavior exhibited by OTKO and wild-type (WT) nullipara toward six 2-4-day-old foster pups during test sessions conducted on 3 successive days. Each day, subjects were placed in a clean cage 30 min prior to introduction of pups which were deposited in a clump adjacent to the middle of a long wall of each test cage. Behavior was measured for 3.5 h after which pups and test subjects were returned to their home cages. On test days 1 and 3, a significantly smaller proportion of OTKO females retrieved pups to a corner of their cage. Also, significantly fewer pups were retrieved to corners by OTKO females. In contrast to most WTs, most OTKO females mothered pups in the center of the cage where they were initially deposited. Pup-licking frequencies were significantly lower in OTKO females. Their self-grooming frequencies also trended toward being lower. Latencies to retrieve and lick pups, latencies to and frequencies of still crouching over pups and proportion of time in nest did not differ between groups. Our findings suggest that OT stimulates a significant proportion of pup-licking in nulliparous mice, a situation similar to lactating rat mothers. Our results also indicate that OT may play a role in the motivation to retrieve pups to a more secure location.     

The effect of cage size and enrichment on core temperature and febrile response of the golden hamster

The aim of this study is to determine the effect of cage size and cage enrichment. Golden hamsters were individually housed in standard cages of four different sizes and in enriched cages of three different sizes since 3 weeks of age. Each of the seven housing groups consisted of 12 hamsters. After 14 weeks of housing in their respective environments the measurements started. The mean baseline rectal temperature was significantly higher in hamsters housed in small cages than in hamsters housed in large cages. After the injection of fever-inducing lipopolysaccharide rectal temperature increased by 1 to 2 degrees C. The increase of rectal temperature and the fever index were the highest in animals housed in large cages and the smallest in animals housed in small cages. Through cage enrichment and increasing cage size the mean febrile response increased while the mean baseline rectal temperature decreased. Cage size and cage enrichment had no effect on the dispersion of the measured values. The differences in microclimate between large and small cages were too small to have an effect on thermoregulation. The results indicate that housing in small cages induce chronic stress which obviously affects thermoregulation. The findings demonstrate that the results of some physiological experiments are significantly influenced by the pre-experimental housing conditions.     

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.     

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 housed mice at three different cage changing frequencies: 7, 14, and 21 days, each at three different cage ventilation rates: 30, 60 and 100 air changes per hour (ACH), for a total of nine experimental conditions. For each condition, we evaluated the health of 12 breeding pairs and 12 breeding trios of C57BL/6J mice for 7 months. Health was assessed by breeding performance, weanling 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 concentrations, relative humidity, and temperature one day prior to changing the cage. The relative humidity, carbon dioxide concentrations, and temperature of the cages at all conditions were within acceptable levels. Ammonia concentrations remained below 25 ppm (parts per million) in most cages, but, even at higher concentrations, did not adversely affect the health of mice. Frequency of cage changing had only one significant effect; pup mortality with pair matings was greater at the cage changing frequency of 7 days compared with 14 or 21 days. In addition, pup mortality with pair matings was higher at 30 ACH compared with other ventilation rates. In conclusion, under the 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.     

Reproductive responses to variation in temperature and food supply by house mice: II. Lactation

Lactating HS/Ibg house mice housed at 21 degrees C and 5 degrees C were assigned to 3 feeding regimes: ad libitum, daily rations of 80% of ad libitum, or 60% of ad libitum beginning on the day that they bore litters. Significant interaction between temperature and food restriction was found for litter survivorship, pup survivorship, litter size, female body weight, and cumulative biomass production. The interaction was due to a magnification of the effects of food restriction at the colder temperature: i.e. mice fed ad libitum were similar at the two temperatures, mice fed the 80% ration differed, and mice fed the 60% ration differed to a greater extent. The dominant response to food restriction was cannibalism by females, which might be associated with the rate of loss in body weight by the female on the days preceding cannibalism of one or more pups. Incidents of cannibalism tended to involve a limited number of pups and to be repeated until a sustainable litter size was reached. In 3 of the food-restricted treatments, females weaned relatively large litters of relatively small pups, but in the most severe treatment (in the group fed the 60% ration at 5 degrees C), the females weaned small litters of large pups. The patterns of cannibalism and variable relative investment in individual pups reflect the aggressive breeding strategy of this classic colonizing species.     

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.     

光周期对布氏田鼠幼仔生长发育的影响

通过比较法对实验室内布氏田鼠 (Microtusbrandti)幼仔生长发育与光周期关系的研究表明 ,尽管出生和断乳时的窝仔数及断乳时窝仔存活率不受光周期的影响 (t test,P >0 0 5 ) ,每种光周期条件下出生和断乳时雌雄比例差异不显著 (Chi square检验 ,P >0 0 5 ) ,不同光周期间雄性比例无明显差异 (百分数的检验 ,P >0 0 5 ) ,但是 ,随着幼仔的生长 ,出生并饲养在长光照周期 (LD ,14L∶10D)下的个体体重、体长和肥满度显著大于短光照周期 (SD ,10L∶14D)下的幼体 ,尤在出生 9或 14天以后的各阶段 (t test,P <0 0 5 )。在 6 0日龄时 ,LD雄鼠的睾丸、附睾及储精囊成熟指数显著高于SD鼠 (t test,睾丸 ,t =3 30 9,df =14,P <0 0 1;附睾 ,t=3 6 2 2 ,df =14,P <0 0 1;储精囊 ,t=3 379,df =14,P <0 0 1)。但LD组的皮毛厚度和绒毛长度显著低于SD组 (t test,皮毛厚度t=- 5 185 ,df =14,P <0 0 1;绒毛长度t=- 2 415 ,df =14,P <0 0 5 )。作者认为体重、肥满度和性腺成熟指数 (GSI)高的LD鼠较SD鼠更适应于繁殖期的繁殖生存 ;而生长发育缓慢 ,皮毛厚度、绒毛长度高的SD鼠更能适应越冬生存。在自然环境中 ,光周期可能被布氏田鼠作为季节环境变化的信号 ,使其在形态和生殖方面提前作好准备 ,采取不同的策略以适     

Behavioural responses of rats to early housing conditions and to protein-energy malnutrition

Lactating rats were fed either the commercial diet (CO) or the low protein diet which induced symptoms of protein - energy deprivation (PD). They were housed in cages either individually (IH) together with eight offspring or in a large community cage (COM) shared by six dams and 48 youngs. After weaning all rats lived in cages by 4-5 animals. The PD terminated at the age of 49 days. Behaviour was tested on the 10th, 42nd and 150 th days of life. Body weight was recorded during nursing period both in dams and pups, after weaning in male rats. The low protein diet affected both body weight and maternal behaviour of the dams. In PD + IH pups growth as well as behavioural development was retarded. Behavioural alterations persisted even after the PD had been treated. The COM housing improved the body weight in the PD + COM dams, behaviour of both the PD + COM dams ond the pups was less affected than of the PD + IH group. The effect of the early housing was long lasting, manifested itself in elevated exploratory activity and in the decreased emotional responses in both the PD + COM and the CO + COM groups at the age of 42 and 150 days.     

The effect of housing and environmental enrichment on stereotyped behavior of adult vervet monkeys (Chlorocebus aethiops)

Little information is available on the response of vervet monkeys to different housing conditions or on the suitability of enrichment devices or methods for vervet monkeys. In this study, the authors evaluated the occurrence of stereotyped behavior in adult vervet monkeys under various conditions of housing and enrichment. The variables included cage size, cage level (upper or lower), enrichment with a foraging log, enrichment with an exercise cage and presence of a mate. The authors first determined the incidence of stereotyped behavior in captive-bred, singly housed adult female and male vervet monkeys. They then exposed monkeys to different housing and enrichment situations and compared the incidence of stereotyped behavior among the monkeys. The authors found that more females than males engaged in stereotyped behavior and that females, on average, engaged in such behavior for longer periods of time than males. Stereotyped behavior was most often associated with a small, single cage. The average amount of observed stereotyped activity in monkeys housed in a small cage was significantly lower when the monkeys had access to either a foraging log or an exercise cage. Stereotyped behavior was also lower in female monkeys that were housed (either with a male or without a male) in a larger cage. The least amount of abnormal behavior was associated with the largest, most complex and enriched housing situation. Males and females housed in cages on the lower level of two-level housing engaged in more stereotyped behavior than did monkeys housed in the upper level, regardless of the presence or type of enrichment provided.     

Postisolation aggression and olfactory cues.

Aggressive maternal behavior was tested by placing intruders in the home cages of 210 individually housed lactating mice 3-8 days postpartum. The intruders were of 6 types: castrated males and females, intact males and females, mothers of 3-8 day old pups, and mothers of older pups. All fights were initiated by the resident lactating female. There were significantly fewer attacks on castrated males than on intact males (p less than .001), and fewer attacks on castrated females than on intact males and females (p less than .001, p less than .01, respectively). There were no attacks on mothers of 3-8 day old pups. Attacks on older mothers were significantly more frequent than on younger mothers (p less than .01). The results indicate that maternal aggression in albino mice is strongly influenced by the hormonal and reproductive state of the intruder.     

The Effect of DNA Repair Defects on Reproductive Performance in Nucleotide Excision Repair (NER) Mouse Models: An Epidemiological Approach

In this study, we used an epidemiological approach to analyze an animal database of DNA repair deficient mice on reproductive performance in five Nucleotide Excision Repair (NER) mutant mouse models on a C57BL/6 genetic background, namely CSA, CSB, XPA, XPC [models for the human DNA repair disorders Cockayne Syndrome (CS) and xeroderma pigmentosum (XP), respectively] and mHR23B (not associated with human disease). This approach allowed us to detect and quantify reproductive effects based on a relatively small number of matings. We measured and quantified the scale of the effect between factors that might influence reproductive performance (i.e. age at co-housing, seasons) and reproductive parameters (i.e. litter size and pairing-to-birth interval –‘pbi’). Besides, we detected and quantified the differences in reproductive performance between wild type mice and heterozygous/homozygous NER mutant mice. From our analyses, we found impaired reproduction in heterozygous and homozygous knock out mice; in particular, reduced litter size and lengthened pbi was related to the NER mutation-mHR23B, in heterozygous couples, even if they were otherwise phenotypically normal. Heterozygous mHR23B couples produced a 6.6-fold lower number of mHR23B^−/− pups than indicated by Mendelian expectation; other genetic deficiencies studied were not statistically significant from each other or wild type controls. We concluded that careful epidemiological evaluations by analysis of animal database could provide reliable information on reproductive performance and detect deviations that would remain unnoticed without this. Also, some managerial aspects of mouse breeding could be evaluated.     

Enrichment materials do not negatively affect reproductive success and offspring survival and weight in mice

Environmental enrichment is designed to improve the overall welfare of laboratory animals, including mice. Few studies have directly assessed the effects of different types of enrichment on mouse offspring survival and growth. The authors examined how survival and growth of C57BL/6 mouse pups are affected by three kinds of cage enrichment materials: compressed cotton squares, two-ply tissues and plastic igloos. During the last week of gestation and the first two weeks postpartum, the authors observed cages with litters and noted use of the enrichment materials, quality of nest construction, number of pups per litter and weight of pups. Both the first and second litters were evaluated for each dam. Dams and pups had continuous contact with the enrichment materials, especially cotton squares and tissues. Neither the presence nor the type of enrichment material influenced the survival and weight of offspring, suggesting that the use of such materials does not negatively impact reproductive success or offspring survival.     

Pregnancy in female house mice exposed to urinary chemosignals from other females.

Seven experiments were performed to investigate pregnancy termination, urinary chemosignals, and litter sex ratio variation in female house mice. Experiments tested the effects of urine from adult and prepubertal females, housed individually or in groups, on successful insemination and litter production by females treated at different times and for different periods during the 3 weeks before mating and during gestation. Treatment of females with urine from adult females housed eight per cage or with urine pooled from eight adult females housed individually for 2 or 3 weeks before mating resulted in fewer successful pregnancies and significantly more female-biased litters. Treatment with urine from adult or prepubertal females housed eight per cage or with urine pooled from eight mice housed individually for the first 6 days of gestation or throughout pregnancy resulted in a significant increase in the rate of pregnancy termination. These treatments resulted in lower body weights at birth and slower growth rates in all males and in some females. Puberty was delayed in female progeny from urine-treated dams in five of seven experiments, and these young females attained first oestrus at greater mean body weights than mice in other treatments. These findings indicate that, in mice, at high population density, communication via a urinary chemosignal can alter reproduction in recipient females. Availability of, and competition for, resources such as food would be greater at higher densities, possibly lowering the probability of reproductive success. Pregnancy termination and delays in reproduction and attainment of sexual maturity might lead to greater successful reproduction at a later time.