Behaviour, social interactions and lesion scores of group-housed sows in relation to floor space allowance

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1 . Applied Animl Behviour Siene Behviour, soil intertions nd lesion sores of group-housed sows in reltion to floor spe llowne R.C. Weng,,), S.A. Edwrds, P.R. English SAC, Cristone Estte, Buksurn, Aerdeen AB1 9YA, UK UniÕersity of Aerdeen, 581 King Street, Aerdeen AB9 1UD, UK Aepted 10 Novemer 1997 Astrt The spe llowne pproprite for sows in group housing remins sientifilly undefined, sine the soil spe requirement of group of nimls nd the ftors whih ffet this re unknown. Eight estlished groups of six pregnnt, multiprous sows were used in replited Ltin Squre design of experiment, with 7 dy periods, to ompre four pen sizes providing.0,.4, 3.6 or 4.8 m rsow. For the lst 48 h of eh 7 dy period, ontinuous video reording ws mde to determine generl ehviour nd ll soil intertions. Time spent rooting inresed progressively with inresing spe llowne, wheres time spent sitting nd stnding intive were oth progressively redued. The totl frequeny of soil intertions nd ggressive ehviour oth inresed with deresing spe llowne. The Attk:Retret rtio ws signifintly higher, nd the Avoidne Index signifintly lower, in the smllest pen. All ody regions hd the highest ount of lesions fter sows hd een in the smllest pen, with dmge levels eing redued s pen re inresed. Anlysis of ody lesion sores, omining inidene nd severity, gve the sme tretment effets. In onlusion, the results indited tht minimum spe of etween.4 nd 3.6 m rsow ws neessry in the onditions of this experiment to promote good welfre. This result nnot e generlised to situtions of different group size, group stility or feeding method. q 1998 Elsevier Siene B.V. All rights reserved. Keywords: Pig-soil ehviour; Spe requirements; Anomlous ehviour ) Corresponding uthor. Ntionl Pingtung University of Siene nd Tehnology, 1 Hsueh-Fu Rod, Lo-Pi, Nei-Pu, Pingtung 9107, Tiwn, ROC r98r$19.00 q 1998 Elsevier Siene B.V. All rights reserved.. PII S

2 308 ( ) R.C. Weng et l.rapplied Animl BehÕiour Siene Introdution The requirement of pig for spe enompsses oth the physil spe tht is oupied y the niml when stnding or lying nd during posture hnges nd, when nimls re housed in groups, dditionl soil spe llowing them to show norml ehviour nd intertions. It is reltively simple to lulte mthemtilly the spe requirements for individul nimls in different postures from the reltionships etween their liveweight nd physil dimensions Petherik, nd spe envelopes when stnding nd lying Bxter nd Shwller, In ddition to their stti spe requirements, nimls generlly require some spe for exerise to mintin musle tone. In the se of pregnnt sows, this filittes prturition Ferket nd Hker, ut the preise exerise need is urrently unknown. The re overed y n extensively kept sow in the ourse of dy n e onsiderle, ut is likely to e hevily influened y the lotion of resoures nd the niml s degree of hunger nd forging motivtion. When the soil group rther thn the individul niml is onsidered, other spe requirements re pprent. These inlude spe for wide rnge of soil intertions inluding the estlishment of dominne Bxter, nd voidne of ggression Ewnk nd Brynt, 197; Jensen, Spe for voidne of potentil ggressors or espe from ttk is vitl for the welfre of low-rnking nimls in group housing. While it hs een demonstrted tht ertin types of housing system with restrited spe llowne n prelude the estlishment of stle soil sitution Jensen, 1984., the preise role of the quntity nd qulity of spe in this ontext is not known. In sitution of unrestrited spe in strw yrd, the distne over whih sows were pursued following ggressive intertions vried from 0 to 0 m Edwrds et l., Even in the sene of overt ggression, enfored proximity to nother sow my in itself e stressful. Hemsworth et l demonstrted hroni stress response in gilts housed t redued spe llowne 1, or 3 m rpig.. Similrly, gilts regrouped t spe llowne of 1 m rpig showed signs of physiologil stress response, i.e., elevted ortisol level nd impired immune response, t 1 dys fter grouping ompred with those grouped t m rpig Brnett et l., Comprle dt do not exist for groups of older, mixed-prity sows. Jensen found inresed ggression with redued spe llowne 1.4,.3 or 3.0 m rpig., ut this study onfounded spe with housing system design stlls, uiles or pen with seprte lying, dunging nd feeding res.. The preferred distne etween individuls will vry, depending on the reltionship of the nimls involved nd their urrent motivtionl stte. Forging sows in extensive onditions mintined n verge distne of 3.8 m etween group memers, nd distne of 50 m etween different groups Stol nd Wood-Gush, In dynmi groups with lrge spe llownes, sows lso mintined loser proximity to previously fmilir individuls thn to strngers Spoolder et l., To ensure sow welfre, housing design must, t the very lest, ensure unimpeded ess to neessry resoures, opportunity to void or espe from potentil ggressors, nd voidne of hroni physiologil stress. The minimum spe llowne neessry for these purposes for sow in group housing remins sientifilly undefined, sine

3 ( ) R.C. Weng et l.rapplied Animl BehÕiour Siene lthough the physil spe oupied during tivities suh s stnding, lying, feeding or mting is well doumented, the soil spe requirement for voidne of ggression, espe, seprtion of speifi tivity res nd explortion, nd the wy in whih suh spe might e time shred within group of nimls is unknown. As eginning to understnding this issue, this study mesured how generl ehviour nd soil intertions were hnged y different floor spe t stndrd group size, in pens with individul feeding stlls, nd relted this to physil inditor of welfre the level of skin lesions.. Mterils nd methods Eight groups of six pregnnt, multiprous sows Lrge White = Lndre, Pig Improvement Compny., formed t wening, were seleted for the experiment t 7 10 weeks post servie. These groups were used in replited Ltin Squre design of experiment, with 7 dy periods, to ompre four pen sizes providing.0,.4, 3.6 or 4.8 m rsow. Sows were fed one dily, t 0700 h, when they were given.7 kg of stndrd dry sow onentrte feed while onfined in individul feeding stlls for period of 1 h. These stlls were then losed off for the reminder of the dy, so tht the sows were onfined to the speified spe llowne in n re edded with deep strw. Spe ws vried y hnging the length of the pen t ommon width of 4.0 m. Wter ws freely ville from single nipple drinker mounted on the rer wll of the pen. At llotion, eh sow ws weighed, suutneous kft thikness t the P position ws mesured ultrsonilly s n index of ody ondition, nd ody length rown to tilhed. nd height t the shoulder were mesured. Skin lesions were sored t the eginning nd the end eh tretment period. At this time, nimls were individully inspeted nd eh lesion srth or ut. ws reorded nd mesured in m. The lesions were drwn on ody mp of eh pig, suh tht hek ould e mde s to whih lesions were dupliting those oserved t the previous reording period, nd whih hd ppered sine tht time. The distriution of lesions ws tegorised into eight ody setions: fe nd ers, nek, shoulder, entrl ody, udder, rump, til, vulv. Eh setion enompssed oth sides of the ody. The severity of dmge in eh setion ws tegorised in five lsses ording to the totl length of lesions: 0snone, 1s1 3 m, s3 6 m, 3s6 9 m, 4s)9 m. For the lst 48 h of eh 7 dy period, ontinuous video reording ws mde of every pen. These reordings were nlysed for generl tivity ptterns y time smpling the ehviour of eh sow t 5 min intervls. All soil intertions were reorded using the ethogrm of Jensen An dditionl tegory of ehviour, thret ws reorded, defined s sudden hed movement or move towrds nother sow whih sumitted or retreted without ontt eing mde. Using these reorded soil intertions, the Attk:Retret rtio ArR. nd Avoidne Index were lulted ording to the method of Jensen On ompletion of the reording period, sows were introdued immeditely to the next tretment. Within the Ltin Squre design, the tretments were pplied in rndom order, nd not ording to progressively inresing or deresing spe llowne.

4 310 ( ) R.C. Weng et l.rapplied Animl BehÕiour Siene Group totls were lulted from the individul sow dt nd were nlysed for the effets of tretment, group nd period using nlysis of vrine. Differenes in the frequeny distriution of different intertion types nd lotion of lesion sores were nlysed using the Chi-squre test Siegel, Results There were no differenes etween time periods in generl ehviour, soil intertions or lesion sores. Signifint differenes did our etween groups in some tegories of ehviour nd intertions, ut not lesion sores. Tle 1 shows the generl ehviour of the sows in reltion to spe llowne. Overll, sows spent most time lying 8%., with most of their tive time eing spent in rooting in the strw edding 37% of non-lying time.. Time spent rooting inresed progressively with inresing spe llowne, wheres time spent sitting nd stnding intive were oth progressively redued. Tle shows the frequeny of soil intertions in reltion to spe llowne. The ehviours of Prllel Pressing nd Inverse Pressing with or without Bites. nd Levering were never oserved throughout the whole experiment. Nose-to-Body ws y fr the most numerous intertion reorded in pens of ll sizes. The totl numer of soil intertions in 48 h, nd the inidene of ggressive ehviour, oth inresed with deresing spe llowne. The frequeny of ll tegories of ehviour exept Nose-to-Nose ws signifintly higher in the smllest pen size. Hed-to-Hed, Hed-to- Body-with-Bite, Nose-to-Body, Nose-to-Genitl nd Hed-Tilt were ll further redued t the lrgest spe llowne. x nlysis indited tht the pooled distriution of types of soil ehviour eight tegories with vlid frequeny of expeted vlues; Tle 1 The effet of pen size on the ehviour of group housed pregnnt sows Pen re m rsow SED Signifine Lying NS Stnding intive 133.4, )) Sitting , ))) Moving NS Rooting 184.0, 05.4, ))) Drinking NS Defeting NS Urinting )) Vlues given re the numer of oservtionsrpen in 46 h the h when sows were onfined in feeding stlls re omitted.. ) s p )) s p ))) s p Mens within rows with different supersripts differ signifintly p

5 ( ) R.C. Weng et l.rapplied Animl BehÕiour Siene Tle The effet of pen size on the frequeny of soil intertions in group-housed, pregnnt sows Pen re m rsow SED Signifine ))) Totl intertions ))) Hed-to-Hed )) Hed-to-Hed-with-Bite )) Hed-to-Body Hed-to-Body-with-Bite ))) Nose-to-Nose NS, ))) Nose-to-Body ,, )) Nose-to-Genitl ))) Thret ))) Hed-Tilt ))) Withdrw )) Attk:Retret rtio Avoidne Index , ) Vlues given re the numer of oservtionsrpen in 46 h the h when sows were onfined in feeding stlls re omitted.. For method of lultion of Indies, refer to Setion. ) s p )) s p ))) s p Mens within rows with different supersripts differ signifintly p Hed-to-Hed-with-Bite nd Hed-to-Body-with-Bite were omined, s were Nose-to-. Nose nd Nose-to-Genitl differed with pen size ll intertions: x s 46.06, df s 1, p When onsidering only ggressive intertions Hed-to-Hed, Hed-to-Body, Bite, or Thret., intertions with Bites ourred t higher frequeny thn expeted in the smllest pen size, whist Hed-to-Body ourred higher thn expeted frequeny in the smllest pen nd lower thn expeted frequeny in the lrgest pen ggressive intertions: x s 5.33, df s 9, p The distriution of Nosing-type intertions. Nose-to-Body or other ws not ffeted y pen size x s1.71, dfs3, p)0.05., nd neither ws the type of sumissive ehviour Hed Tilt or Withdrw. whih ws shown x s0.85, dfs3, p) The Attk:Retret rtio ws signifintly higher, nd the Avoidne Index signifintly lower, in the smllest pen. Tle 3 shows the inidene of skin lesions in reltion to spe llowne. The most ommon sites of ody lesions were the entrl ody, shoulder nd rump. All ody setions hd the highest ount of lesions fter sows hd een in the smllest pen, with dmge levels eing redued s pen re inresed. Anlysis of ody lesion sores, omining inidene nd severity, gve the sme tretment effets s for lesion ounts. The pooled site distriution of ody lesions four tegories s in Tle 3. did not differ etween tretments x s.60, dfs9, p) From the digrms mde t eh reording of the lotion nd length of srthes, it ws pprent tht very few were the sme s t the previous reording nd tht the totl sore ws resonle representtion of the effets of tht tretment. To determine whether the short time period hd

6 31 ( ) R.C. Weng et l.rapplied Animl BehÕiour Siene Tle 3 The effet of pen size on the inidene of skin lesions in group-housed, pregnnt sows Pen re m rsow SED Signifine ))) Totl lesions ))) Fe, ers, nek ))) Shoulder , ))) Centrl ody, udder ))) Rump, til, vulv Totl lesion sore ))) Vlues given re the numer of lesionsrpen t the end of the 7 dy period. For method of lultion of lesion sores, refer to Setion. ) s p )) s p ))) s p Mens within rows with different supersripts differ signifintly p influened the inidene of lesions, the dt reorded for eh group efore ommening the experiment t whih stge they hd een mintined t spe llowne of.4. m rsow sine group formtion ws ompred with the men vlue for the.4 m rsow experimentl tretment. There were no signifint differenes for ny ody region. 4. Disussion When deiding on the dequy of spe for group-housed sows, numer of ftors n e onsidered. The most importnt riteri must e tht there is dequte spe to void physil injury. Although none of the lesions reorded in this experiment were of severe nture, ny inrese in the frequeny of lesions n e onsidered to e n indition of n indequte environment De Koning, Considertion of the lesion inidene nd severity sore. would suggest spe llowne of greter thn.4 m rsow to e neessry under the irumstnes of this experiment. De Koning ws unle to detet differene in lesion sores etween groups of sows mintined t -.5, or )5.0 m rsow, ut his survey involved onfounding of mny other etween-frm ftors suh s group size, floor type nd feeding method. However, lower lesion sores were reorded in very lrge pens )0 m., while no differene ws found etween pens with totl re of -1 or 1 0 m. The two lrger pens in this study exeeded this re, so the results otined re in onordne in this respet. The extent to whih the lowest spe llowne indued physiologil stress ould not e determined in this experiment, sine nimls were not hronilly theterised for stress-free withdrwl of lood smples nd the time period ws too short to onsider lterntive mesures of hnge in drenl funtion or immune response. Study of eh tretment over prolonged period would hve neessitted doption of rndomised lok, rther thn Ltin Squre design, euse of the onstrints imposed y the limited time etween onfirmed pregnny nd frrowing. Sine signifint effets of

7 ( ) R.C. Weng et l.rapplied Animl BehÕiour Siene group were found in nlyses of ehviourl mesures, this would hve involved loss in preision of mesurement of the tretment effets. The dequy of the 7 dy period used in the experiment to detet true tretment differenes might e questioned ut, sine ll groups were well estlished prior to the experiment supposition supported y the sene of time period effets on the mesured prmeters., rpid nd onsistent short term response to hnge in spe would e expeted. The dequy of the experimentl period is lso supported y the high degree of onordne etween lesion sores t the sme spe llowne fter the 7 dy experimentl period nd the 7 10 week pre-experimentl period. The seond riteri for dequy of spe hs een suggested to e norml soil intertion pttern Jensen, The totl numer of soil intertions ws signifintly lower in the lrgest pen thn in ll other tretments. However, when potentilly dmging intertions those involving ites. were onsidered, only the lowest spe llowne resulted in signifint inrese in frequeny. The ility of suordinte sows to perform voidne ehviour hs een suggested s the most importnt ftor regulting soil stility Jensen, The highest frequeny of voidne ehviours Hed-Tilt nd Withdrw. ws seen in the smllest pen, ut it is the reltionship etween ggressive nd voidne ehviours whih is likely to e more importnt. Jensen used two lulted prmeters to evlute this reltionship. The AttkrRetret rtio is prmeter whih, when it hs vlue of less thn 1.0, indites tht nimls re voiding ggressive enounters y showing sumissive ehviour. The vlues otined in this experiment re ll lose to 1.0, ut only the lowest spe llowne gve vlue higher thn 1.0, nd signifintly higher rtio thn ll other tretments. The vlues otined for ll tretments re muh lower thn the vlues of.7 uiles. nd 8. stlls. otined in the more onfined of the housing systems studied y Jensen 1984., proly refleting the ft tht ll pens in the present experiment provided unostruted spe for movement. The vlues re, however, higher thn tht of 0.7 otined in his lest onfined system, whih is surprising in view of the ft tht two of the tretments provided sustntilly more totl nd uninterrupted spe, nd muh higher thn the vlue of 0.1 otined under free-rnging onditions Jensen nd Wood-Gush, The Avoidne Index is mesure of group stility nd expresses the numer of settled pir-reltions i.e., pirs demonstrting unidiretionl intertions. ompred to the totl numer of possile omintions within the group. A vlue of 0.0 mens tht no reltionships re settled, wheres vlue of 1.0 indites ll pirs re settled. The vlue for this index ws gin lower t the smllest spe llowne, inditing n norml soil sitution in estlished groups. The other vlues re generlly omprle to those otined in the lest onfined system of Jensen It n therefore e onluded tht the intertion dt indite spe llowne of.0 m rsow to e indequte for norml soil funtion, ut no signifint enefit to providing dditionl spe ove.4 m rsow. In the pen providing.0 m rsow, the frequeny of intertions ws y fr the highest reorded. Brnett et l found redution in ggressive ehviour when newly mixed, pregnnt gilts were provided with very smll spe llowne m rpig., nd suggested tht limited spe my interfere with or inhiit ggressive ehviour. This ws supported in susequent study with ovrietomised gilts Brnett et l., in

8 314 ( ) R.C. Weng et l.rapplied Animl BehÕiour Siene whih ggression following mixing ws lower in smll retngulr pens 1.4 m rpig. thn in squre pens providing the sme spe llowne or in lrger pens 3.4 m rpig.. However, in oth studies this result relted only to the 90 min following regrouping, nd the susequent totl numer nd severity of lesion sores ws not redued. This suggests tht, while redution in spe my inhiit initil ggression etween unfmilir nimls, the opposite sitution pertins in the longer term in stle groups. Alterntively, if redued spe does result in suppression of soil tivity Brnett et l., 199; Jensen,. 1984, it does not pper tht the lowest spe llowne of.0 m rsow investigted here hd rehed this threshold. While fewer ggressive intertions might e onsidered n indition of good welfre, the use of very limited spe to hieve this is likely to e ssoited with greter hroni soil stress, s indited y the hronilly elevted ortisol levels mesured in gilts with low spe llowne Brnett et l., A third possile riterion for dequy of spe is the expression of unmodified time udgets y the nimls. In this experiment, the frequeny of rooting, the predominnt explortory ehviour, ws redued y deresing spe llowne nd the frequeny of sitting nd stnding intive inresed. The ility to express explortory ehviour hs een onsidered to e n importnt omponent of pig welfre Wood-Gush nd Vestergrd, nd these results would therefore indite tht spe llowne of greter thn.4 m rsow is required for the norml expression of ehviour. In ttempting to generlise from the results of this experiment to other situtions, gret re must e tken. Firstly, it must e orne in mind tht the sows in this experiment were in settled groups prior to ommenement. Aggressive intertions re likely to e more severe, nd the spe requirement for espe nd voidne muh higher, in the period immeditely fter regrouping when reltive dominne is still eing ontested Edwrds et l., The seond qulifying irumstne is tht the sows were individully fed eh dy in protetive feeding stlls. It hs een shown tht the use of feeding stlls n redue mesures of poor welfre, inluding ggression round feeding, lesion sores nd totl plsm ortisol, in groups of reently mixed gilts in smll pens Brnett et l., 1996., nd in stle groups of gilts over omplete pregnny Edwrds et l., Ewnk nd Brynt 197. stted tht sumission nd domintion reltionships were only enfored in ompetition situtions whih, in the se of the pregnnt sow, most ommonly relte to ess to food Edwrds, The spe requirement for sows in system with ompetitive floor-feeding might therefore e very different. In this experiment, the only signifint resoures over whih to ompete would hve een the drinking point lthough wter ws freely ville t ll times. nd preferred spe. The use of strw-edded pens in this experiment might lso hve influened the results otined, sine some studies hve shown provision of roughge to redue ggression in group-housed sows Edwrds, Finlly, the experimentl results relte to only one group size six sows.. With lrger groups, the potentil for time shring of the spe ove tht physilly oupied y the odies of the sows is inresed. With lrger group size nd onstnt spe llowne per sow, the totl pen re is lso inresed. This n llow greter hoie of soil ompnions, voidne of fered individuls nd inresed totl espe re. Suh opportunities re exploited y the nimls, s evidened y the formtion of sptilly distint su-groups within the overll pen re Edwrds et l., 1986; Vn Putten nd vn de Burgwl, The

9 ( ) R.C. Weng et l.rapplied Animl BehÕiour Siene survey results of De Koning 1985 indited the possiility tht totl pen spe might e more importnt thn spe per sow in the voidne of injury. 5. Conlusion The results indite tht minimum spe of etween.4 nd 3.6 m rsow ws neessry in the onditions of this experiment to promote good welfre. This result nnot e generlised to situtions of different group size, group stility or feeding method. Aknowledgements We thnk Mr. A.H. Stewrt nd the stff of Tillyorthie Frm who ssisted with this experiment. SAC reeives finnil support from the Sottish Offie Agriulture, Environment nd Fisheries Deprtment. Referenes Brnett, J.L., Hemsworth, P.H., Cronin, G.M., Newmn, E.A., MCllum, T.H., Chilton, D., 199. Effets of pen size, prtil stlls nd method of feeding on welfre relted ehviourl nd physiologil responses of group-housed pigs. Appl. Anim. Behv. Si. 34, Brnett, J.L., Cronin, G.M., MCllum, T.H., Newmn, E.A., Effets of pen sizershpe nd design on ggression when grouping unfmilir dult pigs. Appl. Anim. Behv. Si. 36, Brnett, J.L., Cronin, G.M., MCllum, T.H., Newmn, E.A., Henessy, D.P., Effets of grouping unfmilir dult pigs fter drk, fter tretment with mperozide nd y using pens with stlls, on ggression, skin lesions nd plsm ortisol onentrtions. Appl. Anim. Behv. Si. 50, Bxter, M.R., Soil spe requirements of pigs. In: Zyn, R. Ed.., Soil Spe for Domesti Animls. Mrtinus Nijhof, The Hgue, pp Bxter, M.R., Shwller, C.E., Spe requirements for sows in onfinement. In: Bxter, S.H., Bxter, M.R., MCormk, J.A.D. Eds.., Frm Animl Housing nd Welfre. Mrtinus Nijhoff, The Hgue, pp De Koning, R., On the well-eing of dry sows. Dotorl thesis, University of Utreht. Edwrds, S.A., 199. Sientifi perspetives on loose housing systems for dry sows. Pig Vet. J. 8, Edwrds, S.A., Muhline, S., Stewrt, A.H., Designing pens to minimise ggression when sows re mixed. Fm. Build. Progr. 113, 0 3. Edwrds, S.A., Brouns, F., Stewrt, A.H Influene of feeding system on the welfre nd prodution of group housed sows. In: Collins, E., Boon, C. Eds.., Livestok Environment IV. Amerin Soiety of Agriulturl Engineers, St. Joseph, MI, pp Edwrds, S.A., Simmins, P.H., Wlker, A.J., Bekett, M.P., Behviour of 400 sows in single group with eletroni individul feeding. Proeedings of the Interntionl Symposium on Applied Ethology in Frm Animls, Bltonfured, Hungry. Ewnk, R., Brynt, M.J., 197. Aggressive ehviour mongst groups of domestited pigs kept t vrious stoking rte. Anim. Behv. 0, 1 8. Ferket, S.L., Hker, R.R., Effet of fored exerise during gesttion on reprodutive performne of sows. Cn. J. Anim. Si. 65,

10 316 ( ) R.C. Weng et l.rapplied Animl BehÕiour Siene Hemsworth, P.H., Brnett, J.L., Hnsen, C., Winfield, C.G., Effets of soil environment on welfre sttus nd sexul ehviour of femle pigs: II. Effets of spe llowne. Appl. Anim. Behv. Si. 16, Jensen, P., An ethogrm of soil intertion ptterns in group housed dry sow. Appl. Anim. Ethol. 6, Jensen, P., 198. An nlysis of gonisti intertion pttern in group housed dry sow ggression regultion through n voidne order. Appl. Anim. Ethol. 9, Jensen, P., Effets of onfinement on soil intertion ptterns in dry sows. Appl. Anim. Behv. Si. 1, Jensen, P., Wood-Gush, D.G.M., Soil intertions in group of free-rnging sows. Appl. Anim. Behv. Si. 1, Petherik, J.C., A iologil sis for the design of spe in livestok housing. In: Bxter, S.H., Bxter, M.R., MCormk, J.A.D. Eds.., Frm Animl Housing nd Welfre. Mrtinus Nijhoff, The Hgue, pp Siegel, S., Non-prmetri Sttistis for the Behviourl Sienes. MGrw-Hill, Tokyo. Spoolder, H.A.M., Buridge, J.A., Edwrds, S.A., Lwrene, A.B., Simmins, P.H., Inditors of soil reognition in gilts mixed into dynmi group of 30 sows. Anim. Si. 6, 630. Stol, A., Wood-Gush, D.G.M., The ehviour of pigs in semi-nturl environment. Anim. Prod. 48, Vn Putten, G., vn de Burgwl, J.A., Pig reeding in phses. In: Eletroni Identifition in Pig Prodution. RASE, Stoneleigh, pp Wood-Gush, D.G.M., Vestergrd, K., Inquisitive explortion in pigs. Anim. Behv. 45,