Behaviour of golden hamsters (Mesocricetus auratus) kept in four ...

Behaviour of golden hamsters (Mesocricetus auratus) kept in four ...

Behaviour of golden hamsters (Mesocricetus auratus) kept in four ...


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85© 2007 Universities Federation for Animal WelfareThe Old School, Brewhouse Hill, Wheathampstead,Hertfordshire AL4 8AN, UKAnimal Welfare 2007, 16: 85-93ISSN 0962-7286<strong>Behaviour</strong> <strong>of</strong> <strong>golden</strong> <strong>hamsters</strong> (<strong>Mesocricetus</strong> <strong>auratus</strong>) <strong>kept</strong> <strong>in</strong> <strong>four</strong>different cage sizesK Fischer † , SG Gebhardt-Henrich* ‡ and A Steiger ‡†Fasanenstrasse 22, CH-4402 Frenkendorf, Switzerland‡Vetsuisse Faculty <strong>of</strong> the University <strong>of</strong> Bern, Division <strong>of</strong> Animal Hous<strong>in</strong>g and Welfare, PO Box Ch-3001, Bern, Switzerland* Contact for correspondence and request for repr<strong>in</strong>ts: sab<strong>in</strong>e.gebhardt@itz.unibe.chAbstractCages for laboratory and pet <strong>hamsters</strong> are usually small. Us<strong>in</strong>g video record<strong>in</strong>gs, the behaviour <strong>of</strong> sixty female <strong>golden</strong> <strong>hamsters</strong>(<strong>Mesocricetus</strong> <strong>auratus</strong>), housed <strong>in</strong>dividually <strong>in</strong> <strong>four</strong> different cage sizes, was compared <strong>in</strong> order to draw conclusions about theirwelfare. The cage sizes were 1,800 cm 2 , 2,500 cm 2 , 5,000 cm 2 , and 10,000 cm 2 . Enrichment items and litter depth were standardisedand all cages were equipped with a runn<strong>in</strong>g-wheel (30 cm diameter). Stereotypic wire-gnaw<strong>in</strong>g, usage <strong>of</strong> the provided space,weight ga<strong>in</strong>, and reactions to mild husbandry stressors were used as welfare <strong>in</strong>dicators. Stereotypic wire-gnaw<strong>in</strong>g was observed <strong>in</strong> allcage sizes, but <strong>hamsters</strong> <strong>in</strong> small cages gnawed significantly longer and more frequently. There were no significant differences <strong>in</strong>runn<strong>in</strong>g-wheel activity. In small cages <strong>hamsters</strong> made use <strong>of</strong> the ro<strong>of</strong> <strong>of</strong> their wooden shelters as an additional platform more <strong>of</strong>tenthan <strong>in</strong> big cages, which could suggest that they needed more space. Therefore, the welfare <strong>of</strong> pet <strong>golden</strong> <strong>hamsters</strong> <strong>in</strong> cages with am<strong>in</strong>imal ground floor area <strong>of</strong> 10,000 cm 2 seemed to be enhanced compared with smaller cages.Keywords: animal welfare, cage size, <strong>golden</strong> hamster, pet animal, runn<strong>in</strong>g-wheel, wire-gnaw<strong>in</strong>gIntroductionGolden <strong>hamsters</strong> (<strong>Mesocricetus</strong> <strong>auratus</strong>) are common laboratoryanimals <strong>in</strong> biomedical research as well as popularpets. Nevertheless, little work has been done with thespecific <strong>in</strong>tent to improve their hous<strong>in</strong>g conditions <strong>in</strong> thelaboratory, and even less is known <strong>of</strong> their hous<strong>in</strong>g requirementsas pets. Exceptions are studies by Bant<strong>in</strong> and Sanders(1989) and Kuhnen (1999a) on cage size, by Mrosovskyet al (1998) on runn<strong>in</strong>g-wheel preferences, by Reebs andMaillet (2003) on environmental enrichment, and the recentreview by Sørensen et al (2005). In the case <strong>of</strong> Kuhnen(1999a), <strong>golden</strong> <strong>hamsters</strong> were <strong>in</strong>dividually housed <strong>in</strong> <strong>four</strong>different cage sizes rang<strong>in</strong>g from 200 to 1,815 cm 2 . Meanfebrile response <strong>in</strong>creased with <strong>in</strong>creas<strong>in</strong>g cage size,whereas mean basel<strong>in</strong>e rectal temperature decreased. Theseresults <strong>in</strong>dicate that hous<strong>in</strong>g <strong>in</strong> small cages <strong>in</strong>duced chronicstress, which affected thermoregulation. The cage sizes usedby Kuhnen (1999a), however, were common for laboratoryrodents but much smaller than the cages used for pet<strong>hamsters</strong>. The Swiss guidel<strong>in</strong>es for pet stores provide a cagesize <strong>of</strong> 1800 cm 2 as the m<strong>in</strong>imum size for <strong>golden</strong> <strong>hamsters</strong>.The Swiss statutory m<strong>in</strong>imum size for one hamster is200 cm 2 . Cage size, ie available space, is <strong>of</strong> great significance<strong>in</strong> regard to the welfare <strong>of</strong> the animals, as shown <strong>in</strong>the studies mentioned above as well as <strong>in</strong> the behaviouraldemand studies by Sherw<strong>in</strong> and Nicol (1997) and Sherw<strong>in</strong>(2003, 2004).Pet rodents spend their whole life <strong>in</strong> their cages and shouldhave the possibility to meet their behavioural needs.Gattermann et al (2001) <strong>in</strong>vestigated the natural habitats <strong>of</strong><strong>golden</strong> <strong>hamsters</strong>. The closest distance between occupiedhamster burrows was 118 m. A mean tunnel length <strong>of</strong>199.5 ± 92.6 cm and a mean burrow depth <strong>of</strong>64.8 ± 17.6 cm were recorded. This shows that the naturalterritory <strong>of</strong> a hamster is considerably larger than any cage.Laboratory <strong>hamsters</strong> did not differ <strong>in</strong> behaviour comparedwith wild caught <strong>hamsters</strong> (Gattermann 2000). Despitedecades <strong>of</strong> domestication they rema<strong>in</strong> capable <strong>of</strong> surviv<strong>in</strong>g<strong>in</strong> a semi-natural environment as demonstrated byGattermann (2000). Therefore, domesticated <strong>hamsters</strong>might need more space than we commonly provide them.Additionally, little is known about the effects <strong>of</strong> handl<strong>in</strong>gand husbandry on the levels <strong>of</strong> stress experienced by pet<strong>hamsters</strong>. In laboratory rodents, rout<strong>in</strong>e handl<strong>in</strong>g andhusbandry procedures have been recognised as potentialstress factors (Balcombe et al 2004). Pet <strong>hamsters</strong> arefrequently caught out <strong>of</strong> their cages by their owners andcarried around. Also, cages are regularly cleaned and movedaround. It is to be expected that <strong>hamsters</strong> <strong>kept</strong> as pets arealso subjected to stressors comparable to rout<strong>in</strong>e handl<strong>in</strong>gprocedures <strong>in</strong> laboratory <strong>hamsters</strong>. Therefore, we also<strong>in</strong>cluded mild husbandry stressors such as handl<strong>in</strong>g andpush<strong>in</strong>g cages around <strong>in</strong> our study. The aim <strong>of</strong> this studywas to analyse behavioural differences <strong>of</strong> <strong>golden</strong> <strong>hamsters</strong>housed <strong>in</strong> different sized cages and subjected to mildUniversities Federation for Animal WelfareScience <strong>in</strong> the Service <strong>of</strong> Animal Welfare

86 Fischer et alFigure 1Timetable <strong>of</strong> the experiment. The stresstreatment was conducted dur<strong>in</strong>g theweeks 11 and 12.husbandry rout<strong>in</strong>e stressors and to draw conclusions abouttheir welfare. <strong>Behaviour</strong> can be a good <strong>in</strong>dicator for thestate <strong>of</strong> welfare <strong>in</strong> animals (Mason 1991; Mason & Mendl1993; but see Mason & Latham 2004). The welfare <strong>of</strong>captive <strong>hamsters</strong> can be assessed by measur<strong>in</strong>g thefrequency and duration <strong>of</strong> wire-gnaw<strong>in</strong>g. Wire-gnaw<strong>in</strong>g <strong>in</strong>mice seems to <strong>in</strong>dicate the <strong>in</strong>tention <strong>of</strong> break<strong>in</strong>g-out <strong>of</strong> thecage to explore the environment (Würbel et al 1998a, b;Nevison et al 1999). It is common <strong>in</strong> <strong>golden</strong> <strong>hamsters</strong> <strong>kept</strong><strong>in</strong> captivity (Gebhardt-Henrich et al 2005). The more ahamster performs this, the more welfare could be compromised.Physiological measurements, such as adrenalhormones and adrenal weight can also <strong>in</strong>dicate stress andwelfare <strong>of</strong> the <strong>golden</strong> hamster. Dur<strong>in</strong>g chronic stress,adrenal weight is <strong>in</strong>creased due to <strong>in</strong>creased hormonalproduction and can, therefore, be a helpful physiologicalparameter <strong>of</strong> stress measurement (Zimmer & Gattermann1986). S<strong>in</strong>ce the study focused especially on pet <strong>hamsters</strong>,cage sizes considerably larger than common laboratorycages were used. Areas <strong>of</strong> cages used <strong>in</strong> this study rangedfrom 1,800 cm 2 to 10,000 cm 2 . The area <strong>of</strong> the smallest cagewas chosen because it provided the m<strong>in</strong>imum for <strong>golden</strong><strong>hamsters</strong> <strong>in</strong> the Swiss pet shop guidel<strong>in</strong>es. An area <strong>of</strong>2,500 cm 2 is a common size for a hamster cage. The SwissAnimal Protection Society (STS) demands a m<strong>in</strong>imum area<strong>of</strong> 5,000 cm 2 and they recommend a cage <strong>of</strong> more than10,000 cm 2 (Lerch-Leemann 2002). In order to reducevariation due to sex, only one sex (female) <strong>hamsters</strong>were used.Materials and methodsAnimals and hous<strong>in</strong>g conditionsThe sixty female <strong>golden</strong> <strong>hamsters</strong> used for this study wereprogeny <strong>of</strong> the stra<strong>in</strong> Crl: LVG (SYR) from Charles River,Germany. Dur<strong>in</strong>g one year the sixty <strong>hamsters</strong> were bred <strong>in</strong>three series <strong>of</strong> 20 <strong>hamsters</strong> each. We used 17 dams and9 sires. The age difference <strong>of</strong> <strong>hamsters</strong> <strong>in</strong> one series wasmostly <strong>four</strong> days, up to a maximum <strong>of</strong> seven. A photoperiod<strong>of</strong> 12 h light, 12 h dark, dawn at 1300h was ma<strong>in</strong>ta<strong>in</strong>ed.Room temperature was 21 ± 2°C, relative humidity was notregulated, but ranged from 25 to 59%. Hamsters used <strong>in</strong> thisstudy were born and raised <strong>in</strong> cages with a wire top and adark blue opaque plastic dishpan as the bottom(95 × 57 × 45 cm; length × breadth × height) without arunn<strong>in</strong>g-wheel. Between 24 and 30 days <strong>of</strong> age, they wereplaced s<strong>in</strong>gly <strong>in</strong>to <strong>four</strong> differently sized cages: Size 1 was32 × 57 × 45 cm (length × breadth × height), ie 1,800 cm 2 ;size 2, 44 × 57 × 45 cm ie 2,500 cm 2 ; size 3, 95 × 57 × 45 cmie 5,000 cm 2 and size 4, 105 × 95 × 45 cm ie 10,000 cm 2 . Allcages were furnished with a wooden shelter(20 × 14 × 14 cm) with one entrance <strong>in</strong> front, litter (15 cmdeep wood shav<strong>in</strong>gs), hay, paper-towels, cardboard tubes,twigs, a sand-bath (diameter: 16 cm, ch<strong>in</strong>chilla sand) and arunn<strong>in</strong>g-wheel (diameter: 30 cm, width <strong>of</strong> perforated metalplate runn<strong>in</strong>g surface: 10 cm). Commercial pet hamster food(Witte Molen®, NL-Meeuwen) and water were <strong>of</strong>feredad libitum. This diet was supplemented by dry cat food andvitam<strong>in</strong> and m<strong>in</strong>eral supplements (Marienfelde Vitakalk). Inaddition, fresh fruits and vegetables were <strong>of</strong>fered daily.Litter was never changed completely. Only the dirty parts <strong>of</strong>the litter were replaced when necessary. Due to spacerestrictions, the experiments were performed <strong>in</strong> three series.Five cages <strong>of</strong> each size were used simultaneously. In each<strong>of</strong> the three series, 20 <strong>hamsters</strong> were distributed s<strong>in</strong>gly <strong>in</strong>the 20 cages. If possible, <strong>hamsters</strong> <strong>of</strong> one litter were placedrandomly <strong>in</strong>to all sizes, but the distribution was balancedaccord<strong>in</strong>g to their body mass <strong>in</strong> cages <strong>of</strong> <strong>four</strong> different sizes.The experiment was approved by the Cantonal Veter<strong>in</strong>aryOffice, Herrengasse 1, CH-3011, Berne, Switzerland.Procedure and measurementsProcedureIn week 0, at wean<strong>in</strong>g, the <strong>hamsters</strong> were approximately4 weeks <strong>of</strong> age. Dur<strong>in</strong>g the experiment they were weighedand videotaped on several occasions (Figure 1).In weeks 11 and 12 each hamster was stressed on twoconsecutive days. At 17 weeks <strong>of</strong> age, the <strong>hamsters</strong> weredecapitated after is<strong>of</strong>lurane-anaesthesia. The stresstreatment started with strongly shak<strong>in</strong>g the cage <strong>in</strong> a mannerthat the hamster was certa<strong>in</strong>ly woken up and probably upset.The animal was then chased briefly and handled for about30 – 60 seconds once caught. Handl<strong>in</strong>g consisted <strong>of</strong> pett<strong>in</strong>gand hold<strong>in</strong>g the hamster which was always keen to retreat.After handl<strong>in</strong>g, the hamster was placed <strong>in</strong>to a smallcardboard box for 30 m<strong>in</strong> and exposed to loud music forthree to five m<strong>in</strong>utes before be<strong>in</strong>g returned to its cage.© 2007 Universities Federation for Animal Welfare

Cage size for <strong>hamsters</strong> 87Figure 2Duration <strong>of</strong> behaviours <strong>in</strong> percent <strong>of</strong> total duration <strong>in</strong> the different cage sizes: a) wheel-runn<strong>in</strong>g, b) rest<strong>in</strong>g, c) rear<strong>in</strong>g, d) groom<strong>in</strong>g, e)wire-gnaw<strong>in</strong>g, f) feed<strong>in</strong>g, g) runn<strong>in</strong>g, h) gnaw<strong>in</strong>g, i) climb<strong>in</strong>g, j) digg<strong>in</strong>g, k) dr<strong>in</strong>k<strong>in</strong>g.Additionally, on the first day <strong>of</strong> stress, half <strong>of</strong> the litter waschanged while, on the second day, a confrontation withanother hamster was <strong>in</strong>stigated. At the end <strong>of</strong> the experiment,immediately prior to euthanasia, the anaesthetisedanimal was stretched out on a ruler and body length (snoutto tip <strong>of</strong> tail) was measured. The body condition <strong>of</strong> thehamster was calculated as bodyweight relative to bodylength (bodyweight at week 13/length 3 ); as a degree <strong>of</strong>adiposis. Blood was collected and analysed for corticosterone,cortisol and ACTH. After dissection the adrenalglands, heart, and spleen were weighed and the gastricmucosa was exam<strong>in</strong>ed for ulcers. As a precaution, all bra<strong>in</strong>swere exam<strong>in</strong>ed for hydrocephalus <strong>in</strong>ternus, as the conditionwas prevalent <strong>in</strong> the colony, although without anydetectable behavioural changes (Edwards et al 2006).Runn<strong>in</strong>g-wheel activityRevolutions <strong>of</strong> runn<strong>in</strong>g-wheels were constantly registeredby the Chronobiology Kit (Stanford S<strong>of</strong>tware Systems).For the analysis <strong>of</strong> the runn<strong>in</strong>g-wheel activity we used themedian <strong>of</strong> the daily revolutions until week 10, prior tostress<strong>in</strong>g the <strong>hamsters</strong>. For the analysis <strong>of</strong> the effects <strong>of</strong> mildstressors, the mean number <strong>of</strong> revolutions dur<strong>in</strong>g the 2 daysthese stressors were applied, as described above, as well as2 days before and after application, were compared.<strong>Behaviour</strong>The behaviour <strong>of</strong> the <strong>hamsters</strong> was recorded 3 times <strong>in</strong>weeks 3, 6 and 10 by us<strong>in</strong>g a light sensitive camera(Ikegami ICD-47E) and a video recorder (Panasonic AG-6730) from 1430 until 1730h. The highest level <strong>of</strong> activityoccurred dur<strong>in</strong>g this period (Fischer personal observation2004). A total <strong>of</strong> thirty m<strong>in</strong>utes <strong>of</strong> active behaviour perrecord<strong>in</strong>g, dur<strong>in</strong>g which period the hamster stayed outsidethe shelter, ie the subject was awake and clearly visible, wasanalysed us<strong>in</strong>g the Observer Version 5.0 (Noldus). Thethirty m<strong>in</strong>utes were split <strong>in</strong>to six × five-m<strong>in</strong>ute observation<strong>in</strong>tervals. If possible, the <strong>in</strong>tervals were equally spaced overthe three recorded hours. If observation <strong>in</strong>tervals could notbe equally spaced over the 3 hours <strong>of</strong> record<strong>in</strong>g, a total <strong>of</strong>thirty m<strong>in</strong>utes, ie 6 <strong>in</strong>tervals <strong>of</strong> the time when the <strong>hamsters</strong>were visible on the tape would, nonetheless, still beanalysed. In some cases 4% (7 <strong>hamsters</strong>, each with 1 observation)<strong>of</strong> <strong>hamsters</strong> were active for less than 30 m<strong>in</strong>utesdur<strong>in</strong>g 3 hours <strong>of</strong> record<strong>in</strong>g, therefore their observationalAnimal Welfare 2007, 16: 85-93

88 Fischer et alTable 1 Post hoc comparisons <strong>of</strong> runn<strong>in</strong>g-wheel activity 2 days before (2BS), 2 days dur<strong>in</strong>g (2DS) and 2 days after (2AS)stressor application.Comparison T-Value P-Value Revolutions per day2AS vs 2BS and 2DS 3.2059 0.0018232AS vs 2BS 2.2127 0.029267 +11882AS vs 2DS 3.3436 0.001177 +2115.362BS vs 2DS 1.1617 0.248200 +927.36The number <strong>of</strong> revolutions per day <strong>in</strong>dicate how many additional revolutions on average <strong>hamsters</strong> made dur<strong>in</strong>g the <strong>in</strong>dicated 2 days (firstcolumn first term <strong>in</strong> comparison with the other two days (first column second term).Table 2 Number <strong>of</strong> <strong>hamsters</strong> mak<strong>in</strong>g use <strong>of</strong> the ro<strong>of</strong> <strong>of</strong> their wooden shelter.Cage size (cm 2 ) Observed on shelter Not observed on shelter n1,800 14 1 152,500 12 2 145,000 5 10 1510,000 4 11 15Total 35 24 59(χ 2 3= 22.05, P < 0.0001). One hamster whose wheel was non-function<strong>in</strong>g was deleted.Table 3 The mean (± SD) concentrations <strong>of</strong> hormones <strong>in</strong> the serum <strong>of</strong> female <strong>golden</strong> <strong>hamsters</strong> <strong>in</strong> 4 different cagesizes.Cage size (cm 2 ) n Corticosterone(ng ml –1 )Cortisol(ng ml –1 )Corticosterone/cortisolcoefficientACTH(pg ml –1 )1,800 14 7.74 ± 5.43 8.94 ± 6.64 1.34 ± 0.94 9.64 ± 15.312,500 13 7.41 ± 4.48 8.88 ± 6.12 1.73 ± 1.56 12.85 ± 11.105,000 15 7.44 ± 5.10 8.25 ± 7.21 1.79 ± 2.67 15.20 ± 13.4310,000 14 6.76 ± 3.51 7.29 ± 6.67 1.26 ± 1.14 13.00 ± 14.61Table 4 The mean (± SD) masses <strong>of</strong> organs <strong>of</strong> female <strong>golden</strong> <strong>hamsters</strong> <strong>in</strong> 4 different cage sizes.Cage size (cm 2 ) n Adrenals (µg) Heart (mg) Spleen (mg)1,800 14 7.98 ± 1.67 0.53 ± 0.07 0.14 ± 0.032,500 13 8.22 ± 2.33 0.54 ± 0.06 0.13 ± 0.015,000 15 9.01 ± 2.27 0.53 ± 0.07 0.03 ± 0.0210,000 15 8.54 ± 2.18 0.50 ± 0.05 0.18 ± 0.22data was based purely on the time they were active. As one<strong>of</strong> the <strong>hamsters</strong> <strong>in</strong> cage size 2 was never active dur<strong>in</strong>g therecorded time, behavioural data for this animal are miss<strong>in</strong>g.The <strong>hamsters</strong> were observed cont<strong>in</strong>uously and the observedbehaviours, and locations <strong>of</strong> behaviours with<strong>in</strong> the cage,were classified follow<strong>in</strong>g Vonlanthen (2003). <strong>Behaviour</strong>aldata were expressed as the percentage <strong>of</strong> total observedtime, ie 90 m<strong>in</strong>, for all three record<strong>in</strong>gs (total percentduration). Furthermore, mean durations <strong>of</strong> bouts, andfrequencies <strong>of</strong> bouts were analysed. The open space <strong>of</strong> acage was def<strong>in</strong>ed as the area <strong>of</strong> the cage exclud<strong>in</strong>g anystructures like the runn<strong>in</strong>g-wheel, shelter, food bowl, sandbath, or wire.Statistical analysesAll statistical analyses were made with NCSS® 2001, orSAS® 8.02 (SAS Institute, Cary, NC). Data and residualswere checked for normality and transformed if necessaryand possible. If normality <strong>of</strong> residuals could not beachieved, non-parametric tests were used. Transformationsand tests are described <strong>in</strong> the results. Experimental series (1-3) and the occurrence <strong>of</strong> hydrocephalus were <strong>in</strong>cluded asfactors <strong>in</strong> the analyses <strong>of</strong> behavioural data and are onlymentioned if they had a significant <strong>in</strong>fluence. Correlationswere calculated by us<strong>in</strong>g Spearman rank correlation coefficients.One hamster was excluded from the behaviouralanalyses s<strong>in</strong>ce her wheel was malfunction<strong>in</strong>g over a long© 2007 Universities Federation for Animal Welfare

Cage size for <strong>hamsters</strong> 89Figure 3Frequency dur<strong>in</strong>g 30 m<strong>in</strong> observationsdur<strong>in</strong>g the active time <strong>of</strong> wire-gnaw<strong>in</strong>gbouts <strong>of</strong> <strong>in</strong>dividual <strong>hamsters</strong> <strong>in</strong> the differentcage sizes. Raw data are shown, butfor the analyses the data were squareroot transformed.Figure 4Duration <strong>of</strong> wire-gnaw<strong>in</strong>g (% <strong>of</strong> the totalobservation duration) <strong>in</strong> the 4 cage sizes.Boxes represent the central 50% <strong>of</strong> thedata, the horizontal l<strong>in</strong>e represents themedian, the vertical l<strong>in</strong>es show 1.5 timesthe <strong>in</strong>terquartile range, dots are valuesoutside this range, and stars representthe mean value <strong>of</strong> total duration whichwas 19.3% for 1,800 cm 2 , 14.5% for2,500 cm 2 , 9.55% for 5,000 cm 2 , and 4.2%for 10,000 cm 2 . Raw data are shown, forthe analyses the data were transformedas per Figure 3.period <strong>of</strong> the experiment, which could have had an<strong>in</strong>fluence on her behaviour.Results<strong>Behaviour</strong>Hamsters devoted most <strong>of</strong> their active behaviour to wheelrunn<strong>in</strong>g.The rema<strong>in</strong><strong>in</strong>g time was spent ma<strong>in</strong>ly on rest<strong>in</strong>g,rear<strong>in</strong>g and groom<strong>in</strong>g (Figure 2).The results <strong>of</strong> the different behavioural activities are listedbelow. The occurrence <strong>of</strong> hydrocephalus as a ma<strong>in</strong> factorwas never significant. There was no immediate <strong>in</strong>fluence <strong>of</strong>the stressors on the behaviour <strong>of</strong> the <strong>hamsters</strong>.Runn<strong>in</strong>g-wheel useAll <strong>hamsters</strong> used the runn<strong>in</strong>g-wheel. The average distancewas 8.3 km per day (8872 revolutions). The m<strong>in</strong>imum peranimal was on average 0.63 km per day; the maximum was18.56 km per day. These distances are not equivalent tolocomotion <strong>in</strong> a cage or <strong>in</strong> the natural habitat (Sherw<strong>in</strong>1998a). Dur<strong>in</strong>g the 10 weeks before the stress treatment,runn<strong>in</strong>g-wheel activity <strong>of</strong> <strong>hamsters</strong> was not significantlydifferent <strong>in</strong> all 4 cage sizes (ANOVA, F = 0.88, n = 59, ns).However, the more a hamster ran <strong>in</strong> the wheel, the less itgnawed at the wire (r s= –0.7105, n = 59, P < 0.0001) orclimbed (r s= –0.7261, n = 59, P < 0.0001). The runn<strong>in</strong>g-Animal Welfare 2007, 16: 85-93

90 Fischer et alFigure 5Mixed model REML <strong>of</strong> weight ga<strong>in</strong> fromwean<strong>in</strong>g to week 13 with cage size andseries as factor variables. Raw data areshown, for the analysis the data were logtransformed. In a pairwise comparison, thedifference between the smallest and thelargest cages was significant (P < 0.05).wheel data dur<strong>in</strong>g the two days <strong>of</strong> stress and the runn<strong>in</strong>gwheeldata <strong>of</strong> the two days after the stress treatment werethen compared with the runn<strong>in</strong>g-wheel activity on the twodays before the stress was applied.The stress treatment affected runn<strong>in</strong>g-wheel activity significantly<strong>in</strong> all cage sizes. Dur<strong>in</strong>g the two days after stresstreatment, runn<strong>in</strong>g-wheel activity was significantly higherthan before and dur<strong>in</strong>g stressor application (RepeatedMeasures ANOVA, n = 45, P = 0.0068, F = 5.31) (Table 1).From time-to-time some <strong>hamsters</strong> blocked the runn<strong>in</strong>gwheelwith litter and <strong>in</strong> certa<strong>in</strong> <strong>in</strong>stances the runn<strong>in</strong>g-wheelwas not function<strong>in</strong>g or the transmission <strong>of</strong> data failed. Thesedata were excluded from the analyses. Furthermore, allrunn<strong>in</strong>g-wheel data <strong>of</strong> one hamster <strong>in</strong> cage size 2 wereexcluded because the transmission <strong>of</strong> the runn<strong>in</strong>g-wheeldata failed consistently.The total duration <strong>of</strong> wheel-runn<strong>in</strong>g observed <strong>in</strong> the record<strong>in</strong>gswas significantly correlated with the median <strong>of</strong> therevolutions per day measured with the Chronobiology Kit(r s= 0.60, n = 58, P < 0.0001).Wire-gnaw<strong>in</strong>gCompared with gnaw<strong>in</strong>g at various structures (cardboardtube, twigs, shelter, etc) the <strong>hamsters</strong> gnawed at the wire forlonger periods (Wilcoxon Signed Rank Test: Z = 4.3439,P < 0.0001). The mean duration <strong>of</strong> wire-gnaw<strong>in</strong>g was7.6 ± 2.7 s and the mean duration <strong>of</strong> gnaw<strong>in</strong>g at other structureswas 0.9 ± 0.7 s. While 13 out <strong>of</strong> 59 (22%) <strong>hamsters</strong>showed both behaviours, 17 (29%) showed only wiregnaw<strong>in</strong>g,3 (5%) gnawed exclusively on other material thanwire, and 26 <strong>hamsters</strong> were never observed gnaw<strong>in</strong>g onanyth<strong>in</strong>g. There was no significant effect <strong>of</strong> cage size on thenumber <strong>of</strong> <strong>hamsters</strong> perform<strong>in</strong>g wire-gnaw<strong>in</strong>g. For furtheranalyses a m<strong>in</strong>imum threshold for duration (1% <strong>of</strong> totalobserved time) was def<strong>in</strong>ed to exclude <strong>hamsters</strong> that onlybit <strong>in</strong>to the bars briefly. Hamsters <strong>in</strong> small cages gnawedmore frequently at the wire than <strong>hamsters</strong> <strong>in</strong> larger cages(ANOVA, square root transformation: n = 22, F = 3.35,P = 0.05) (Figure 3).Total duration <strong>of</strong> wire-gnaw<strong>in</strong>g was significantly longer <strong>in</strong>small cages (Mixed model us<strong>in</strong>g REML, transformationy 1 = 2 ars<strong>in</strong>√y: n = 22, F = 14.00, P = 0.002) (Figure 4).Compar<strong>in</strong>g the smallest and the biggest cage size the differencewas significant (Tukey’s Studentized Range Test forpercent duration: P < 0.05). Furthermore, wire-gnaw<strong>in</strong>g waspositively correlated with climb<strong>in</strong>g (Spearman rank correlationcoefficient [r s] = 0.7180, n = 59, P < 0.0001), which<strong>in</strong>dicates that <strong>hamsters</strong> that used to gnaw on the wire alsoused to climb on the wire. Total duration <strong>of</strong> wire-gnaw<strong>in</strong>gwas positively correlated with f<strong>in</strong>al bodyweight (r s= 0.43,n = 22, P = 0.04).LocationHamsters spent most <strong>of</strong> their active time <strong>in</strong>side the runn<strong>in</strong>gwheel(58% <strong>in</strong> 1,800 cm 2 , 74% <strong>in</strong> 2,500 cm 2 ,63% <strong>in</strong> 5,000 cm 2 and 70% <strong>in</strong> 10,000 cm 2 ) (Figure 2). Thesedifferences were not significant. The rema<strong>in</strong><strong>in</strong>g time wasspent <strong>in</strong> the open space, at the wire, <strong>in</strong> the food bowl, on theshelter, or <strong>in</strong> the sand-bath. In small cages, more <strong>hamsters</strong>were observed at least once on top <strong>of</strong> the ro<strong>of</strong> <strong>of</strong> their shelter(Fisher’s Exact Test, n = 59, χ 2 = 22.05, P < 0.0001) (see3Table 2), but the total duration on top <strong>of</strong> shelters as well asthe total frequency <strong>of</strong> shelter ro<strong>of</strong> use did not differ amongcage sizes (ANOVAS, all P > 0.1).The use <strong>of</strong> the open space was much more pronounced <strong>in</strong>big cages (ANOVA, n = 59, P = 0.0187, F = 3.66). Thewhole area <strong>of</strong> all the cages was used regularly.© 2007 Universities Federation for Animal Welfare

Cage size for <strong>hamsters</strong> 91BodyweightAt week 0 bodyweights did not differ significantly <strong>in</strong> all<strong>four</strong> cage sizes (ANOVA, log-transformation: n = 60,F = 2.65, P = 0.14). Weight ga<strong>in</strong> from wean<strong>in</strong>g untilweek 13 was significantly reduced <strong>in</strong> big cages (Mixedmodel on log-transformed weight ga<strong>in</strong>s: n = 57, P = 0.01,F 3, 32= 4.53) (Figure 5). Series, age at wean<strong>in</strong>g, and littersize had no effect on weight ga<strong>in</strong>. Body condition also didnot differ significantly between cage sizes (ANOVA:n = 57, F = 1.93, P = 0.14). Dur<strong>in</strong>g autopsy, no difference<strong>in</strong> the amount <strong>of</strong> fatty tissue was noticed.Stress hormones and organ weightsNeither plasma stress hormone levels nor the coefficient <strong>of</strong>cortisol/corticosterone differed between cage sizes (P > 0.1)(Table 3). No differences were found <strong>in</strong> organ weights<strong>in</strong>clud<strong>in</strong>g the weights <strong>of</strong> the adrenal glands (Table 4).DiscussionThe aim <strong>of</strong> this study was to analyse behavioural differences<strong>of</strong> <strong>golden</strong> <strong>hamsters</strong> housed <strong>in</strong> different sized cages andsubjected to mild husbandry rout<strong>in</strong>e stressors and to drawconclusions about their welfare. Size related differences <strong>in</strong>wire-gnaw<strong>in</strong>g, use <strong>of</strong> the ro<strong>of</strong> <strong>of</strong> their shelter as additionalspace, use <strong>of</strong> open space, and weight ga<strong>in</strong> <strong>in</strong>dicated reducedwelfare <strong>in</strong> small cages. Our <strong>in</strong>vestigations showed that,although <strong>hamsters</strong> displayed wire-gnaw<strong>in</strong>g <strong>in</strong> all cage sizes,<strong>hamsters</strong> <strong>in</strong> small cages performed wire-gnaw<strong>in</strong>g more<strong>of</strong>ten and for longer periods. In small cages, more <strong>hamsters</strong>made use <strong>of</strong> the ro<strong>of</strong> <strong>of</strong> their shelter which could <strong>in</strong>dicatethat additional space was <strong>in</strong>creas<strong>in</strong>g welfare. The use <strong>of</strong>open space was much more pronounced <strong>in</strong> larger cages andthe whole area <strong>of</strong> the larger cages was used regularly. Thecage size did not <strong>in</strong>fluence runn<strong>in</strong>g-wheel activity <strong>of</strong><strong>hamsters</strong>. This was expected because rodents value wheelrunn<strong>in</strong>gvery much as shown <strong>in</strong> an operant test with mice(Sherw<strong>in</strong> 1998b).Hamsters gnawed longer and more frequently on the wirethan on other objects <strong>in</strong> their cage. Gnaw<strong>in</strong>g on cardboardtubes, twigs or the wooden shelter serves several purposes,such as help<strong>in</strong>g abrasion and clean<strong>in</strong>g <strong>of</strong> the teeth and alsoto produce nest<strong>in</strong>g material, provide food fibre, etc (Fischerpersonal observation 2004). Some <strong>hamsters</strong> shredded thecardboard tube and used its pieces as nest<strong>in</strong>g material. Incontrast, wire-gnaw<strong>in</strong>g seemed to be <strong>in</strong>effective; it couldnot be prevented by provid<strong>in</strong>g natural material to chew on,so wire-gnaw<strong>in</strong>g and gnaw<strong>in</strong>g at objects presumably have adifferent cause and/or function. Wire-gnaw<strong>in</strong>g might be anattempt to escape from the cage (Nevison et al 1999,Würbel et al 1998a, b), but it can also be <strong>in</strong>terpreted as redirectedbehaviour at a replacement object and thus as anabnormal behaviour, or even as a stereotypy. Stereotypicbehaviour is commonly def<strong>in</strong>ed as repetitive, unvary<strong>in</strong>gbehavioural patterns without obvious goal or function(Ödberg 1987), <strong>in</strong> animals <strong>kept</strong> under barren hous<strong>in</strong>g conditions(Mason 1991). Stereotypies are <strong>of</strong>ten observed <strong>in</strong>captive rodents (Würbel & Stauffacher 1996, 1997, 1998;Wiedenmayer 1997; Waibl<strong>in</strong>ger 1999) and are common<strong>in</strong>dicators <strong>of</strong> poor welfare (eg review by Mason 1991;Würbel 2001). Wire-gnaw<strong>in</strong>g <strong>in</strong> <strong>hamsters</strong> <strong>in</strong> the presentstudy was repetitive, <strong>in</strong>variant, performed at a particularspot on the wire top <strong>of</strong> the cage (Würbel et al 1996), andwithout function. Even if this behaviour is not considered astereotypy but an attempt to escape from the cage, it is stillan <strong>in</strong>dication that the wire-gnaw<strong>in</strong>g <strong>hamsters</strong> were notcontent with their hous<strong>in</strong>g.Therefore, the results <strong>of</strong> this study <strong>in</strong>dicated that hous<strong>in</strong>g <strong>in</strong>big cages improved the welfare <strong>of</strong> the <strong>hamsters</strong> because itresulted <strong>in</strong> less wire-gnaw<strong>in</strong>g. The biggest cage, with a size<strong>of</strong> 10,000 cm 2 , was the one with the shortest duration <strong>of</strong>wire-gnaw<strong>in</strong>g as well as the lowest frequency. Duration andfrequency <strong>of</strong> wire-gnaw<strong>in</strong>g <strong>in</strong> 10,000 cm 2 was half <strong>of</strong> thatseen <strong>in</strong> 5,000 cm 2 cages, albeit non-significantly. However,even though <strong>hamsters</strong> <strong>in</strong> small cages performed more wiregnaw<strong>in</strong>gthan <strong>hamsters</strong> housed <strong>in</strong> bigger cages, wiregnaw<strong>in</strong>goccurred <strong>in</strong> all cages. This suggests that even acage <strong>of</strong> 10,000 cm 2 was too small for female <strong>golden</strong><strong>hamsters</strong>. If we estimate the natural territory size from them<strong>in</strong>imum distance between occupied burrows <strong>in</strong> Syria, ourbiggest cages represented a mere 0.007% <strong>of</strong> it.The positive correlation between wire-gnaw<strong>in</strong>g andclimb<strong>in</strong>g can be expla<strong>in</strong>ed by the preference <strong>of</strong> some<strong>hamsters</strong> to climb to a particular spot on the front or the top<strong>of</strong> the cage to gnaw on the wire. Some <strong>hamsters</strong> used toclimb while paus<strong>in</strong>g dur<strong>in</strong>g wire-gnaw<strong>in</strong>g. They usuallyclimbed up and down the front side <strong>of</strong> the wire top but thenreturned to the same po<strong>in</strong>t and restarted wire-gnaw<strong>in</strong>g.Climb<strong>in</strong>g was considered as the source behaviour pattern<strong>of</strong> stereotypic wire-gnaw<strong>in</strong>g <strong>in</strong> laboratory mice (Würbelet al 1996).In addition to behavioural observations, physiologicalparameters could be useful to assess the welfare <strong>of</strong> the<strong>golden</strong> <strong>hamsters</strong>. The health <strong>of</strong> the animals is an importantfactor for welfare. Obesity and its negative consequencesare common <strong>in</strong> pets. Therefore it is important to give<strong>hamsters</strong> the appropriate cage size, where the risk <strong>of</strong> obesityis m<strong>in</strong>imised. Possible reasons for the higher weight ga<strong>in</strong> <strong>in</strong>small cages could be lower energy expenditure and/orgreater food <strong>in</strong>take. Faster runn<strong>in</strong>g <strong>in</strong> big cages, which usesmore energy, would expla<strong>in</strong> the higher energy consumption.Hamsters <strong>in</strong> smaller cages ga<strong>in</strong>ed more weight and wereobviously able to spend more energy on growth. At anadvanced age excessive energy will not be used for growth,at which po<strong>in</strong>t adiposis could become a problem <strong>in</strong> smallcages. The lack <strong>of</strong> a runn<strong>in</strong>g-wheel or other activities withthe possibility for high energy expenditure, could further<strong>in</strong>crease adiposis. Therefore, cage sizes 1 and 2 seem tohave been too small for the hous<strong>in</strong>g <strong>of</strong> pet <strong>hamsters</strong>.The lack <strong>of</strong> significant differences <strong>in</strong> hormonal levels couldbe due to methodological problems (Gebhardt-Henrich et alsubmitted). Due to the sensitivity <strong>of</strong> hormonal measurementsto (sometimes unknown and unavoidable) environmentalfactors, <strong>in</strong>terpretations <strong>of</strong> the stress levels <strong>of</strong> <strong>golden</strong><strong>hamsters</strong> based on these hormones must be made withcaution. It is probable that several problems contribute toAnimal Welfare 2007, 16: 85-93

92 Fischer et althe difficulties <strong>of</strong> <strong>in</strong>terpret<strong>in</strong>g hormonal measurements withregard to stress and these have been discussed sufficientlyelsewhere (Buchanan & Goldsmith 2004; Rushen 1991).However, the measurements <strong>of</strong> adrenal glands suggest thatstress levels did not differ between cage sizes. The stressexperienced as a result <strong>of</strong> common disturbances, mimickedby our stressor treatments, might not be <strong>in</strong>fluenced by thesize <strong>of</strong> the cage. Alternatively, 13 weeks <strong>in</strong> the differentcages might not have been sufficient to result <strong>in</strong> differentlysized adrenal glands. The lack <strong>of</strong> any significant effect <strong>of</strong>stressors on behaviour could also mean that the stressorswere not strong enough to elicit a response. However, thestress treatment <strong>in</strong>creased (short-term) runn<strong>in</strong>g <strong>in</strong> the wheel.There are numerous <strong>in</strong>terpretations <strong>of</strong> the causes <strong>of</strong>runn<strong>in</strong>g-wheel activity (see the review by Sherw<strong>in</strong> 1998a).A possible explanation is that the situation dur<strong>in</strong>g the stresstreatment was aversive to the <strong>hamsters</strong> and they tried toescape from the area. Runn<strong>in</strong>g <strong>in</strong> the wheel might haveprovided the illusion that they could leave the area. Thepossibility that runn<strong>in</strong>g <strong>in</strong> the wheel helped reduce experiencedstress is one that lies beyond the scope <strong>of</strong> this paperand rema<strong>in</strong>s the subject <strong>of</strong> an ongo<strong>in</strong>g study.Compared with other studies, all cages <strong>in</strong> our study wereenriched. All cages were furnished with the same structures(enrichment), but there was still more free space <strong>in</strong> bigcages. In big cages, <strong>hamsters</strong> had the possibility to runlonger distances, whereas enrichment items and the chanceto perform other behaviours were the same <strong>in</strong> all cages. Itwould be <strong>in</strong>terest<strong>in</strong>g to see whether stereotypic wiregnaw<strong>in</strong>gwould persist <strong>in</strong> big cages with more enrichment.Ödberg (1987) found that an <strong>in</strong>crease <strong>in</strong> cage size did notaffect stereotyped jump<strong>in</strong>g <strong>in</strong> voles, whereas enrichmentwith twigs reduced it. Although jump<strong>in</strong>g is not analagous towire-gnaw<strong>in</strong>g <strong>in</strong> <strong>hamsters</strong> it shows that the structure <strong>of</strong> theenvironment can be <strong>of</strong> greater importance to caged animalsthan the size <strong>of</strong> the cage. Spangenberg et al (2005) housedrats either s<strong>in</strong>gly <strong>in</strong> small cages (1,092 cm 2 ) with only oneblack plastic tube, or <strong>in</strong> groups <strong>in</strong> larger cages (3,938 cm 2 )which were provided with more and various enrichment.Rats <strong>in</strong> larger, more enriched cages displayed a morediverse behavioural repertoire which consisted <strong>of</strong> runn<strong>in</strong>g,climb<strong>in</strong>g and social behaviours. The size <strong>of</strong> a cage andenrichment are not <strong>in</strong>dependent. Big cages <strong>of</strong>fer more possibilitiesand space for enrichment than small cages. Moreenrichment items might lead to less stereotypic behaviourand improve animal welfare (eg Ödberg 1987; Würbel et al1998; Kuhnen 1999b). The comb<strong>in</strong>ation <strong>of</strong> a big cage witha correspond<strong>in</strong>g amount <strong>of</strong> enrichment could be an evenbigger improvement <strong>of</strong> welfare <strong>in</strong> <strong>golden</strong> <strong>hamsters</strong>.The well-be<strong>in</strong>g <strong>of</strong> caged animals is affected by manyfactors (Bant<strong>in</strong> & Sanders 1989). Weiss and Schtick 1982(<strong>in</strong> Bant<strong>in</strong> & Sanders 1989) showed that rats prefer to live<strong>in</strong> big, narrow cages compared to big, broad cages.Although our cages were much bigger than the cages <strong>in</strong>the mentioned study, the shape <strong>of</strong> the cage could also beimportant for <strong>hamsters</strong>.The available free space was used <strong>in</strong> all cage sizes.Hamsters <strong>in</strong> the two bigger cages used the whole groundarea and spent more time <strong>in</strong> the open space than <strong>hamsters</strong> <strong>in</strong>the two smaller cages. However, the <strong>hamsters</strong> <strong>in</strong> the twobigger cages used to walk along the walls, so that trails wereformed. Thigmotaxis (ie stay<strong>in</strong>g close to the walls andavoid<strong>in</strong>g the centre <strong>of</strong> an area) is common <strong>in</strong> rodents andsometimes used as an <strong>in</strong>dex <strong>of</strong> anxiety (Simon et al 1994;Syme & Hughes 1972). Therefore one explanation is that<strong>hamsters</strong> <strong>in</strong> bigger cages explored more than <strong>hamsters</strong> <strong>in</strong>smaller cages, despite an <strong>in</strong>herent fear <strong>of</strong> open spaces.A further factor is an additional platform <strong>in</strong>side the cage.The Swiss Animal Protection (SAP) postulates an <strong>in</strong>sertedfloor <strong>in</strong> small cages <strong>in</strong> order to enlarge the available space.The additional space on top <strong>of</strong> the wooden shelter wasused by almost every hamster <strong>in</strong> the two smallest cages.On the contrary only a few <strong>hamsters</strong> <strong>in</strong> the bigger cagesused the elevated platform. Although duration andfrequency did not differ significantly, this suggests that<strong>hamsters</strong> <strong>in</strong> the two smallest cage sizes may have used thetop <strong>of</strong> the wooden shelter as additional space, whereas<strong>hamsters</strong> <strong>in</strong> the bigger cages seemed to have enough spaceand preferred to stay on the floor.All <strong>hamsters</strong> used the sand-bath for groom<strong>in</strong>g regularly, butnot exclusively. Most <strong>hamsters</strong> wallowed <strong>in</strong> the sand. Thusa sand-bath seems very important for the welfare <strong>of</strong> <strong>golden</strong><strong>hamsters</strong>, whether housed <strong>in</strong> small or big cages.Conclusions and animal welfare <strong>in</strong>dicationsS<strong>in</strong>ce the frequency and duration <strong>of</strong> wire-gnaw<strong>in</strong>g wassignificantly higher <strong>in</strong> smaller cages than <strong>in</strong> the large cages,the welfare <strong>of</strong> pet <strong>golden</strong> <strong>hamsters</strong> might be improved byprovid<strong>in</strong>g enriched cages <strong>of</strong> at least 10,000 cm 2 . Further<strong>in</strong>vestigations should address the behaviour and development<strong>of</strong> stereotypic wire-gnaw<strong>in</strong>g <strong>of</strong> <strong>golden</strong> <strong>hamsters</strong> <strong>in</strong>differently enriched cages.AcknowledgmentsExtensive comments from Eva Waibl<strong>in</strong>ger (SAP) greatlyimproved the manuscript. We are grateful to the Institute <strong>of</strong>Veter<strong>in</strong>ary Pathology at the University <strong>of</strong> Berne forallow<strong>in</strong>g us to use their premises. Furthermore, we wouldlike to thank Zeljiko Kragic and Rolf Dürrenwächter fortheir technical help. The paper is based on the dissertationwith the same title by KF <strong>of</strong> the Vetsuisse Faculty Bern,Switzerland. This work was supported and f<strong>in</strong>anced by theSwiss Federal Veter<strong>in</strong>ary Office SFVO. Grant number:973.256 2.03.04.ReferencesBalcombe JP, Barnard ND and Sandusky C 2004Laboratory rout<strong>in</strong>es cause animal stress. Contemporary Topics <strong>in</strong>Laboratory Animal Sciences 43: 42-51Bant<strong>in</strong> GC and Sanders PD 1989 Animal cag<strong>in</strong>g: Is big necessarilybetter? Animal Technology 40: 45-54Buchanan KL and Goldsmith AR 2004. Non<strong>in</strong>vasiveendocr<strong>in</strong>e data for behavioural studies: the importance <strong>of</strong> validation.Animal <strong>Behaviour</strong> 67: 183-185© 2007 Universities Federation for Animal Welfare

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