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Effects of family housing on some behavioural and physiological parameters of juvenile farmed mink ( Mustela vison
  Effects of family housing on some behaviouraland physiological parameters of juvenilefarmed mink (  Mustela vison ) Sari Ha¨nninen*, Jaakko Mononen, Sanna Harjunpa¨a¨,Teija Pyyko¨nen, Juhani Sepponen, Leena Ahola University of Kuopio, Department of Biosciences, P.O. Box 1627, FIN-70211 Kuopio, Finland  Accepted 5 March 2007Available online 10 April 2007 Abstract Farmedminkaretraditionallyweanedattheageof6–8weeksandthekitsliveinmale–femalepairsuntilpelting time (approximately 6 months of age). It is possible that keeping an entire litter together with thedam in a row-cage system until pelting could provide the juvenile mink with some form of socialenrichment, lasting maternal contact and a more diverse physical environment. We compared traditionalpair housing of mink in standard mink cages (P group, 13 litters) with family housing in row-cage systemswhere several standard mink cages were connected to each other via openings in the nets separating thecages (F group, 13 litters). The F kits were housed in families of five to nine siblings and their mother. The Pkits were housed in male–female pairs. Animal density was the same for both groups. Therewere altogether41 F male, 33 F female, 31 P male and 31 P female kits, and 13 F and 13 P dams in the experiment.At the end of the study, the F kits had more bite scars (score 3.5  0.2 for males and 4.3  0.2 forfemales) than the P kits (males 1.1  0.1, females 1.3  0.1) ( P < 0.05), indicating that aggression mayhave been more common in family-housed than pair-housed kits. The mass of adrenals (males F:107  5 mg versus P: 123  6 mg, females F: 105  5 mg versus P: 107  5 mg,  P < 0.01) and serumcortisol levels after ACTH administration (439  28 nmol/l versus 448  32 nmol/l, 457  31 nmol/lversus 501  31 nmol/l, respectively,  P  = 0.067) were lower in F than P kits, which might indicate thattheFkitshadexperiencedlesslong-termstressthanthePkits.Thehousingsystemhadnoeffectonthebodymass of the kits at any time points when they were weighed, although feed consumption was lower in the FgroupthaninthePgroup(209  38 g/(d animal)versus248  15 g/(d animal))inNovember( P < 0.01).Inthelateautumn,withsub-zerotemperatures,theFanimalstypicallyhuddledtogetherinonenestbox,whichmay have provided them with thermoregulatory benefits. These benefits might partially explain thedifference in the function of the HPA-axis between the two groups. To conclude, although aggression www.elsevier.com/locate/applanimApplied Animal Behaviour Science 109 (2008) 384–395* Corresponding author. Tel.: +358 40 517 7844. E-mail address:  sari.hanninen@uku.fi (S. Ha¨nninen).0168-1591/$ – see front matter # 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.applanim.2007.03.002  was a severer problem in family than pair housing, the problems were altogether milder than in some earlierstudies. The mink kits housed as families might have been less stressed than the pair-housed kits, but thestress results were rather ambiguous. # 2007 Elsevier B.V. All rights reserved. Keywords:  Fur farming; Mink; Group housing; Welfare; Fur damage 1. Introduction Mink is the main animal species kept for fur in theworld. Over 25 million mink kits are raisedevery year (European Commission, 2001). It has been argued that the farming conditions of themink are far from the ideal.In the wild, the mink (  Mustela vison ) is a solitary and territorial animal (Birks, 1986;Dunstone, 1993; Niemimaa and Pokki, 1997), which ferociously defends its territory. At matingtime, in February and March, the males circulate into the territories of the females. A male mayguard a female for a few days after the mating, after which the male will move on searching foranotherfemale.Thekits,usuallyfromthreetosix,areborninMayorJune(NiemimaaandPokki,1997). They become nutritionally independent of their mother at 5–6 weeks of age, after whichthey hunt with their mother for a few weeks. The kits disperse at the age of 8–12 weeks (Birks,1986; Dunstone, 1993, see Nimon and Broom, 1999). Accordingly, if one encounters a group of  mink in nature, it is most likely a female hunting with her kits.Despite the fact that in the wild the mink can be aggressive towards its con-specifics (Birks,1986; Dunstone, 1993; Niemimaa and Pokki, 1997), farming practice has shown that juvenileanimals can be housed successfully in pairs or triplets (European Commission, 2001; Nimon andBroom, 1999). On farms, kits are weaned from their mother at 6–8 weeks of age. They may beweaned directly into male–female (usually brother–sister) pairs, or kept in litters until 11–12weeks of age before splitting them into pairs. Kits may also be kept in groups of three fromweaning (in July) to pelting (in November or December). One or two male siblings may also behoused with their mother. After pelting, all animals, i.e. the breeding stock, are housed singly.Early weaning of the mink kits may impair their welfare by increasing the incidence of tailbiting and stereotypies (Mason, 1994; Jeppesen et al., 2000). Nimon and Broom (1999) proposed that a study should be instigated to examine whether weaning could be postponed until the kitsare 11 or 12 weeks old. In the Netherlands, delayed weaning, at least until 11 weeks of age, isalready regulated by the law (see Vinke et al., 2002), and about 20% of the mink are alreadyhoused from birth until pelting as entire litters with their mothers in cage systems where onefamily has access to several traditional cages connected with openings (see a review in theEuropean Commission, 2001). There is also an increasing trend in the Nordic countries topostpone weaning to 8 weeks (European Commission, 2001).Earlier studies of the welfare effects of both ‘family housing’ (litter with the dam) and ‘grouphousing’ (litter without the dam) have produced contradictory results. Some Danish studiesindicate that aggression may be a problem in both family (Pedersen, 1999; Pedersen et al., 2004) and group (Hansen et al., 1997) housing conditions. Family housing may also jeopardise thewelfare of the mother, indicated by an elevated plasma cortisol level, higher level of fur damageand poorer teat condition (Pedersen and Jeppesen, 2001). On the other hand, in Dutch studiesexperiences of family housing have been mainly positive (de Jonge, 1996a,b; de Jonge andIwardeen, 1995; all cited in Nimon and Broom, 1999). S. Ha¨ nninen et al./Applied Animal Behaviour Science 109 (2008) 384–395  385  The contradictory results from the Netherlands and Denmark indicate that further research onthe welfare of mink in group or family housing systems is needed. Thus we undertook this studywhere the welfare effects of housing mink from birth to pelting in litters with their mothers werecomparedwith the traditional pair housing of the kits. Welfarewas assessed bybehavioural (bothdirect and indirect) and physiological measures. Although the dams were included in bothexperimental groups, the main emphasis was on the welfare of the kits. 2. Material and methods 2.1. Animals and housing conditions The experiment was carried out at the Juankoski Research Station of the University of Kuopio. It wasaccomplished in an animal barn with eight rows of mink cages. In May, wild colour type mink dams gavebirth in standard mink cages (30 cm  71 cm  38 cm,  W    L    H  ) with a wooden nest box(29 cm  27 cm  30 cm) with straw as bedding. The nest box was situated in the front of the cage,i.e. nearest to the corridor between the cage rows. Twenty-six litters with their mothers (age 1–5 years) wereselected to the study from the whole mink population of the farm (58 litters) and these were divided evenlyinto family- (F group,  N   = 13 families) and pair-housed (P group,  N   = 13 families) families. The groupswerematchedaccordingtothelittersizeandbirthdateofthekits.Thereweresixandsevenprimiparousandsevenandsixmultiparous(2yearsold:5and4,3yearsold:1and1,4yearsold:0and1,5yearsold:1and0)dams in the F and P group, respectively.In the F group, the litters (  N   = 13) with their mothers were maintained as families. These families weremoved to row cage systems when the kits were 6 weeks old. The row cage systems were formed byconnectingstandardminkcagestoeachotherwitha10 cmlongplastictubeof10 cmdiameter.Thetunnelwas in the upper rear part of the cage and access to the tunnel was from a wire-mesh platform(18 cm  30 cm,  W    L  ; 23 cm above the cage floor) situated on the rear wall of the cage (i.e. furthestfrom the corridor). The animals were housed in the density which is traditionally used during the growingseason in mink,i.e. two mink per cage. Thenumberof animals included in the F familiesvaried between 6and 10, and thus the number of cages in a row cage system varied between 3 and 5. (Any extra kits wereremoved from the families when they were 8 weeks old.) Typically therewere more male than female kitsin the F families: one more in eight families and three more in one family. In the remaining four families,there was one female kit more than there were male kits.Anothersetof13familieswashousedinthetraditionalway(thePgroup).Thekitswereweanedattheageof 8 weeks andsubsequentlythe dams were housedalone andthe kits inbrother–sister pairsin standard mink cages.ThePgroupanimalswereplacedinadjacentstandardcagesinonecagerowsothateachPfamilyhadanFfamilyofthesamelittersizeandage(i.e.itsmatchedpair)ontheothersideofthecorridorseparatingthetwocagerows.TherewereasmanycagesoccupiedbyeachPfamilyastherewerecagesoccupiedbythematchedFfamily.Forexample,anFfamilywithadamanditssevenkitshadarowcagewithfourcages,anditsmatchedPfamilyhadthreecagesforthekits(male–femalepairineach)andonecageforthedam.ThenumberofanimalsincludedinaPfamilyvariedbetweenfive(damplustwomale–femalekitpairs)andnine(damplusfourmale–female kit pairs). Any extra kits were removed also from the P families.There were a total of 136 kits (41 F males, 33 F females, 31 P males and 31 P females) and 26 dams (13family-housed and 13 solitary-housed) in the experiment. All animals were marked in June withsubcutaneous microchips (Indexel, Digital Angel Corporation).Nest boxes with straw bedding were available in all cages of both groups throughout the study. TheanimalswerefedwithfreshfuranimalfeedtwiceadayuntiltheendofSeptember andonceadaythereafter.The feed contained fish, slaughter offal, grain, protein mixture, oils, water and vitamin-iron addition and itwas manufactured according to the recommendations of Finnish Fur Breeders’ Association. The animalswere fed  ad libitum , i.e. there were leftovers from the previous day when the animals were fed for the firsttimethe nextday.Thefeedwas deliveredonthe roofsofthecages.IntheF group,thedailyfeed portionwas S. Ha¨ nninen et al./Applied Animal Behaviour Science 109 (2008) 384–395 386  divided evenly on the roofs of all cages available to a family. Water was available  ad libitum  until it froze inNovember and after that water was served twice a day. The general health of the animals was checked daily,and special attention was paid on fights or injuries to ensure that mink whose health was threatened wereseparated in time. 2.2. Data collected  The behavioural observations of the animals were performed by one and the same observer familiar tothe animals. She walked slowly and calmly along the corridor and scanned animals in each cage for a fewseconds in order to observe the behavioural state (active or passive) and position (nest box, front part of thecage, rear part of the cage, platform, and for the F group in which cage or nest box) of each individualanimal. An animal was regarded as being passive, if it was lying; only its head was allowed to move. Otherbehaviours were regarded as activity. Stereotyped behaviour (pacing and head-twirl with hind legsstationary, see e.g. Mason, 1993) and aggressive acts (violent contacts) were also observed. Matched FandPfamilieswerealwaysobservedassimultaneouslyaspossible,andittookonlyafewminutestoscanallthe 26 litters. The observations were performed three times (at 8–9 a.m., depending on light conditions,11 a.m. and 2 p.m.) during each test day and altogether on 5 days from August to November (at thebeginning of August, beginning and end of September, end of October and end of November). Since theindividuals (in the F group) could not be identified during these observations, the results were calculated aspercentages of animals within each family in each of behavioural category: resting in the nest box, active inthe nest box, resting in the cage, active in the cage, aggressive acts and stereotyped behaviour. To simplifythe presentation of the results, data from the three tests per each day were also combined by calculating theaverages for the behavioural states within each family.Grouppreference index(GPI)wascalculated fortheF familiesasdescribedby Gatterman(1990).GPIisa comparative value of the preference for staying in groups, and it is based on the number of pair-wiserelations within a group. GPI ranges from 0 (all individuals alone) to 100 (all individuals together) percent.Two mink were considered to be together, if they were in the same part of a cage (front, back or platform) orinthesamenestbox.TheaverageGPIforeachfamilywascalculatedfromthethreeobservationsduringoneobservation day.The dirtiness of the nest boxes and straw bedding in the box was recorded every second week fromAugust to November and scored on a subjective five-point scale from 0 (clean) to 4 (extremely dirty). At thesame time, the nest boxes were manually cleaned, dirty or wet bedding was removed and fresh beddingadded.The feed consumption of the families of both groups was measured twice, once in September and againin November. The daily  ad libitum  portions and leftovers were weighed (accuracy 1 g) during a 4-dayperiod.Theresultswerecombinedfromthese4daysandconvertedtodailyfeedconsumptionperanimalforeach family (F or P) per day.The kits and the dams were weighed (accuracy 1 g) when the kits were 6 weeks old (in June), inSeptember, in October and in November (at pelting when the kits were 27–30 weeks old).At pelting, the kits were injected (i.m.) with 0.06 ml synthetic ACTH (Synacthen–Depot 1 mg/ml, Ciba)to induce maximum cortisol production (ACTH-test, see e.g. Terlouw et al., 1997) and then killed 2 h later.TheamountofACTHgiventoeachanimalwasanoverdose(atleast0.026 mg/kg 0.75 )toensurethemaximalsecretion of cortisol toblood. The kits were killed by electrocution according to the recommendations of theEuropean Convention (1998). Death was ensured by immediate neck dislocation after the electrocution.Blood samples were drawn by heart puncture immediately after death and serum was analysed for cortisol(Coat-A-Count Cortisol Assay by Diagnostic Products Corporation, Los Angeles, CA).The kits were pelted and the severity of scars, assumed to be caused by biting, was recorded from theleather side of the fleshed skins. A subjective scale from zero to fivewas used: 0 = no scars; 1 = one to threesingle small holes, scars or red spots; 2 = more than three single holes, scars or red spots; 3 = as 2, but inaddition small areas with innumerable amounts of holes or scars; 4 = large areas with innumerable amountsof holes or scars; 5 = almost the whole skin covered with holes and scars. The length of the dried skin was S. Ha¨ nninen et al./Applied Animal Behaviour Science 109 (2008) 384–395  387  measured (accuracy 0.5 cm) from the tip of the nose to the base of the tail. The severity of fur chewing andbite damages separately in tail and body were analysed by using subjective scale from zero to five: 0 = nodamage, 1 = rather minor damage, 2 = minor damage, 3 = moderate damage, 4 = rather severe damage and5 = severe damage. The professionals of the Finnish Fur Sales Co. Ltd. recorded fur defects.The corpses were autopsied and the mass of adrenals (accuracy 0.1 mg) was measured. The mass of adrenals may be used as a measure of stress in animals (Selye, 1950; Go´mez et al., 1996; Hemsworth et al.,1996).The severity of fur chewing and bite damages separately in tail and body was recorded from the dams inNovember with using dichotomous scale: 0 = no chewing or bite damages, 1 = chewing or bite damagesfound. Note that there are no other individual measurements from the dams except the body weight and thefur chewing and bite damages, since the dams were used for breeding also in the following year. 2.3. Statistical analyses and presentation of the results Each F family had a P family that was matched for litter size and age of the kits, and therefore thesematched families were not independent of each other. Furthermore, litter mates were, of course, notindependent. The data concerning body size, mass of adrenals, serum cortisol level after administration of ACTH, scars, fur chewing, bite damages and fur defects were collected from individual animals, whereasthe values of the remaining dependent variables (behavioural data, dirtiness of nest boxes and feedconsumption) srcinated from groups of animals.The effects of experimental group and sex on body mass, mass of adrenals, serum cortisol level and skinlength were analysed with Linear Mixed Model (SPSS statistical software) (  N   = 136). These variablesfulfilled the demands of the test. Litter, matched pair and relative amount of males in each cage/row cagewere used as random factors. Body mass in November was used as a covariate when analysing mass of adrenals and serum cortisol level.The rest of the parameters were tested with non-parametric tests. Because of the dependence betweenanimals within each family and each matched-pair, the data from individual animals were combined bycalculating mean values from the values of individual animals before testing of differences in scars and furchewing in tail and body. This was done separately for both sexes within each family. The percentages of mink within a litter and within a sex with defects were calculated for the comparisons of the fur defects.Thus, four dependent variables were produced for each skin parameter: F males, F females, P males and Pfemales. Accordingly,  N   is 13 (i.e. the number of matched families) although the data in fact srcinates from136 kits. After this the results were analysed with Friedman test, and pair-wise comparisons of F males, Pmales, F females and P females were performed with a  post hoc  test presented in Siegel and Castellan(1988).The behavioural data (activity/resting, GPI and stereotypies), feed consumption and the data concerningthe dirtiness of the nest boxes were compared with Wilcoxon matched-pairs test if the two groups werecompared, or with Friedman two-way analyses of variance if time trends (i.e. repeated measurements) wereanalysed.  N   is 13 (i.e. the number of matched families) also in these analyses, although the data is from 136kits.Body mass gain of the dams was analysed with paired samples  t  -test (  N   = 12; because one female fromone matched pair died). Fur chewing in tail in dams (  N   = 12) was tested with Fisher’s exact test. Mortalityresults (kits and dams pooled) were also tested with Fisher’s exact test. P -values lower than 0.05 are regarded as significant,  P -values between 0.05 and 0.1 as tendencies ortrends, and  P -values greater than 0.1 as being non-significant (NS). The results are presented as mean orestimated marginal mean  standard error of mean (S.E.M.). 2.4. Ethical note The experiment was approved by the Institutional Animal Care and Use Committee of the University of Kuopio (licence number 99-44). S. Ha¨ nninen et al./Applied Animal Behaviour Science 109 (2008) 384–395 388
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