Color Preferences of Laboratory Mice for Bedding Materials ...

Exp. Anim. 61(2), 109–117, 2012—Original—Color Preferences of Laboratory Mice for BeddingMaterials: Evaluation Using RadiotelemetryKohei Kawakami 1) , Bing Xiao 2) , Rei-ichiro Ohno 1) , Mohammed Z. Ferdaus 2) ,Miki Tongu 1) , Kazuo Yamada 3) , Takaya Yamada 1) , Masato Nomura 4) ,Yuta Kobayashi 1) , and Toru Nabika 2)1) Department of Experimental Animals, Center for Integrated Research in Science, Shimane University, 89–1Enya-cho, Izumo, Shimane 693-8501, Japan2) Department of Functional Pathology, Faculty of Medicine, Shimane University, 89–1 Enya-cho, Izumo, Shimane693-8501, Japan3) Department of Biochemistry, Faculty of Medicine, Shimane University, 89–1 Enya-cho, Izumo, Shimane 693-8501,Japan4) Department of Biotechnology and Chemistry, Faculty of Engineering, Kinki University, 1 Takaya Umenobe,Higashi-hiroshima, Hiroshima 739-2216, JapanAbstract: Preferences for different housing conditions in mice were evaluated by radiotelemetry.Male C57BL/6J and ICR mice were used. Preference for bedding materials in mice was comparedamong three materials, wood shavings (WS), paper (CF) and cloth (AG), using the length of stay incages as a parameter. The results indicated that mice stayed longer in a cage with AG than in cageswith other bedding materials. The present study confirmed our previous results and thereby indicatedthat radiotelemetry is a useful method to evaluate impacts of housing conditions on animal welfare.In the second part of this study, we used radiotelemetry to evaluate color preference of the mice forcloth bedding material. In C57BL/6J mice, staying time in black cloth was significantly longer thanthat in white cloth. In ICR mice, staying time in white cloth was significantly longer than that in blackcloth. The mice preferred the environment with the same color as their fur, which may be importantfor animal welfare.Key words: color preference, housing conditions, mice, telemetryIntroductionHousing conditions may affect the well-being oflaboratory animals as well as experimental results. Anappropriate environment is essential for the expressionof natural behaviors in animals. Therefore, maintaininggood standardized housing conditions may improve thecomparability and reproducibility of the outcomes ofanimal experiments [3, 6].Over recent decades, laboratory mice have providedsubstantial opportunities for researchers to performvarious biomedical studies because of their similarity tohumans, short life cycle and small size [21]. In spite ofthis, the effects of housing conditions on the physiologyand behavior of mice were not carefully evaluated formany years. The selection of a bedding material is acrucial aspect in environmental enrichment that promotesthe expression of natural behaviors and reducesabnormal behaviors [25].Many researchers have sought to improve cage designsby accommodating conditions for the exhibitionof species-specific behaviors [14, 34, 39]. The majority(Received 23 June 2011 / Accepted 18 October 2011)Address corresponding: K. Kawakami, Department of Experimental Animals, Center for Integrated Research in Science, Shimane University, 89–1Enya-cho, Izumo 693-8501, Japan© 2012 Japanese Association for Laboratory Animal Science

COLOR PREFERENCES OF MICE FOR BEDDING MATERIALS 111Fig. 1. The preference test system with mice. (A) Types of cage floor covering. From left to right: wood shavings(WS, Clean-chip TM ), paper (CF, Care-feeaz TM ), cloth (AG, Agrebe TM ). (B) Types of cage floorcovering. From left to right: black cloth (Agrebe TM ), white cloth (Agrebe TM ). (C) Two-direction device:two identical test cages connected to a central cage. (D) Three-direction device: three identical testcages connected to a central cage.half was for data acquisition. Staying time and activitywere recorded every 10 min. Preference for the beddingmaterials was assessed by calculating staying time percage, and resting time was defined as a period with noactivity.Experimental procedureExperiment 1: Experiments were designed to comparetwo bedding materials in C57BL/6J mice. As shown inFig. 1C, the preference tests consisted of three groupcomparisons: WS and CF, CF and AG, and AG and WS.The time course of experiments is shown in Fig. 2. Micewere randomly allocated to three groups as shown in thefigure to avoid bias due to the experimental order. Experimentswere started using mice at the age of 8 weeks.Experiment 2: Experiments were carried out to comparethe three bedding materials in C57BL/6J mice (Fig.1D); preference tests consisted of one group comparison:WS, CF, and AG. Experiments were started using miceat the age of 8 weeks.Experiment 3: Using the apparatus shown in Fig. 1C,experiments were carried out to compare the two colorsFig. 2. Experimental design for experiment 1.(black cloth and white cloth) in terms of the preferencesof C57BL/6J and ICR mice (Fig. 1B). Experiments werestarted using mice at the age of 8 weeks.Statistical analysisData are expressed as means ± SEM. Differences weretested with analysis of variance (ANOVA) and theScheffe post hoc test. Analyses were performed usingStatView (SAS Institute Inc., Cary, NC, USA). A P

112K. KAWAKAMI, ET AL.Fig. 3. Comparison of the period of stay of mice in each combination of bedding materialsunder light and dark phases using a two-direction device. Data represent means ± SEM(n=12). **: P

COLOR PREFERENCES OF MICE FOR BEDDING MATERIALS 113Fig. 5. Comparison of locomotor activity of mice in each combination of bedding materialsunder light and dark phases using a two-direction device. Data represent means ± SEM(n=12). **: P

114K. KAWAKAMI, ET AL.Fig. 6. Comparison of behavior of mice in three floor combinationsof bedding materials using a three-direction device.(A) Staying time, (B) resting time, and (C) activity. Datarepresent means ± SEM (n=12). * and **: P

COLOR PREFERENCES OF MICE FOR BEDDING MATERIALS 115ing and hiding within the cloth bedding material. Bytheir periods of stay among the three cages containingWS, CF, and AG, a difference in kinds of behavior ofthe mice between the light and dark periods was suggested(Fig. 6A and 6C). In both experiment 1 and experiment2, mice were found to strongly prefer the clothbedding material compared with the other materials. Asimilar result was obtained in our other study in whichboth male and female ICR mice had a strong preferencefor the cloth bedding materials compared with the othermaterials [33]. This suggests that the flexibility, hygroscopicity,and heat-retaining properties of cloth are comfortablefor mice [23]. However, compared with woodshavings or paper, observation of an animal in the clothbedding material cannot be carried out easily [22].In experiment 3, we used C57BL/6J and ICR mice.C57BL/6J mice are an inbred strain; they are commonlyused for embryo transfer and intergenic recombination,so we also utilized this strain here; although ICRmice are from a closed colony, we used them here forthe fundamental study of the bedding materials of mice[22, 24, 32]. Laboratory mice showed clear and consistentindividual preferences for cloth bedding materialsimilar in color (black and white) to the fur of strains ofboth C57BL/6J and ICR mice. However, this does notexplain why mice preferred places with a similar colorto their fur; it could have been motivated by fear via aconditioned place preference mechanism. Among mammals,trichromatic vision has only been observed inprimates. This is because they have three types of conephotoreceptor, each of which is maximally sensitive toshort (S), middle (M), or long (L) wavelengths of light[31]. Most mammals, including mice, are dichromats,possessing only S and M cone pigments, and thereforethe brains of mice did not need to evolve to make thesediscriminations [20, 37]. Relatively little is known aboutcolor vision in mice. In a recent investigation on colorpreferences, Sherwin et al. [35] reported that CBA micepreferred a white cage the most and a red cage the least.The preference for white contradicts results by Martinezet al. [27] and Arnedo et al. [2], who reported that, beforeconditioned place preference tests, mice preferred blackover white places. Their visual apparatus is basicallysimilar to that of humans [10, 29], and the retinal ganglioncells have spectral sensitivity in the range of360–640 nm [18]. Cone photoreceptor cells of highervertebrates act under daylight conditions, and their characteristiccolor sensitivities are attributed to the visualpigments having unique absorption spectra [30]. Someresearchers have suggested that mice have the capacityfor color vision [17], but others have made inconclusivestatements such as “whether mice have color vision isan open question” [1]. However, to ensure good welfare,we must understand the requirements of the animals, forwhich bedding material similar in color to their fur ispreferable.Measuring the strength of preference by examiningthe strength of motivation for a certain option makespreference tests even more valuable [36, 38]. Behavioralobservations in the home cage can be used to studysuch factors as differences in the behavioral repertoireafter changing the living conditions of the animals.Animal well-being is, in general, related to a broad behavioralrepertoire, meaning that assessment of an animal’swell-being requires a thorough knowledge of theanimal’s species-specific behavior and biology.In conclusion, the present study indicated that radiotelemetryis a useful approach for evaluation of environmentalpreferences in laboratory mice. The preferencetest for the colors (black and white) of cloth beddingmaterials showed that the C57BL/6J mice preferred stayingin black cloth and that the ICR mice preferred stayingin white cloth, namely, in materials with protectivecoloring. 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