IMPACT OF THE NON CASTRATION OF MALE PIGS ON GROWTH PERFORMANCE AND BEHAVIOUR- COMPARISON WITH BARROWS AND GILTS

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1 61st Annul Meeting of the Europen Assocition for Animl Production August 23 rd -27 th, 2010 Herklion, Crete Islnd, Greece Session 17 "Symposium: Alterntives to cstrtion in pigs" pper 8 IMPACT OF THE NON CASTRATION OF MALE PIGS ON GROWTH PERFORMANCE AND BEHAVIOUR- COMPARISON WITH BARROWS AND GILTS Quiniou N., Courbouly V., Slün Y., Chevillon P. IFIP - Institut du Porc, BP 35104, Le Rheu cedex, Frnce Corresponding uthor: nthlie.quiniou@ifip.sso.fr ABSTRACT Growth performnce, crcss qulity, behviour nd generl condition of crossbred (Pietrin x Lrge White) x (Lrge White x Lndrce) bors, brrows nd gilts fed d libitum nd group-housed were compred from wening until slughter. During the postwening nd the fttening periods, pigs were group-housed (8-9 or 6 pigs/pen, respectively). Pigs were ll slughtered on the sme dy. Between 28 nd 63 d of ge (post-wening period), growth performnce ws not significntly influenced by the gender. Between 63 nd 152 dys of ge (fttening period), dily feed intke of bors ws lower thn tht of brrows (2.41 nd 2.70 kg/d, respectively). Their verge dily gin ws similr nd not significntly different (1032 nd 1069 g/d, respectively), even if brrows presented higher growth rte t the beginning of the fttening period. Consequently, cstrtion ws ssocited with n increse of feed conversion rtio (2.62 vs. 2.26) nd crcss ftness. Gilt feed conversion rtio (2.48) ws intermedite between those of bors nd brrows. According to simultions performed with the InrPorc softwre over the kg body weight rnge, the digestible lysine requirement per unit of net energy intke ws on verge 0.1 g/mj higher for bors thn for gilts nd brrows. Brrows were less ctive thn gilts nd bors nd hd more leg problems t the end of the fttening period (lmeness, bursitis). Bors presented higher lesion scores (wounds/scrtches) during the first six weeks of fttening nd more socil behviour. Gilts were more interested by pen fetures thn by other pigs. Economic context needs to be considered in order to decide if dietry nutritionl vlues hve to be dpted on the bsis of bor requirements or if specific diets hve to be provided to bors nd gilts. More knowledge is required to chrcterise the bor behviour nd generl condition under restricted feeding conditions or when slughtering occurs in different conditions (older pigs, mny deprtures to the slughter house). INTRODUCTION Over the lst yers, the surgicl cstrtion of mles without nesthesi ws more nd more questioned in Europe with regrd to niml welfre considertions (Fredriksen et l., 2008). An lterntive to cstrtion could consist in the production of intct mles, s provided tht the bor tint problem cn be solved. In such context, questions rise, especilly in countries where only gilts nd brrows were bred trditionlly, bout their performnce, nutrient requirements, behviour, nd body condition in comprison with the two other genders. Differences between bors nd brrows or between bors nd gilts (Hnsen nd Lewis, 1993; Lbroue et l., 1994; Noblet et l., 1994; Xue et l., 1995; Quiniou et l., 1996) hve been extensively investigted in the 90's. Over the lst decdes, the verge level of growth performnce hs drmticlly chnged in response to the genetic selection for lener pigs. Subsequently, new dt re required to updte the effect of the gender on the dynmic of growth nd feed intke. Some recent studies were crried out on different genders but they only focused on two genders or presented only verge growth performnce. In ddition, the ntgonistic behviour nd mounts seem to be more frequently observed in mles thn in brrows or gilts (Cronin et l., 2003), which cn result in deteriorted body condition. In such context, the present experimentl progrm ws crried out to chrcterize the growth performnce, the behviour nd body condition of bors in comprison with brrows nd gilts, when group-housed nd fed d libitum. 1. MATERIALS AND METHODS 1.1. Experimentl design The experiment ws crried out in the experimentl unit of IFIP (Romillé, 35, Frnce) on crossbred pigs, progeny of Lrge White x Lndrce sows inseminted with semen of crossbred Lrge White x Pietrin sires. The pigs were studied from 63 d of ge until slughter, bove 110 kg BW. The performnces of growing bors were compred to those of brrows nd gilts when fed d libitum during the post-wening nd the fttening periods. Behviour nd body condition were chrcterised during the fttening period. Pigs of different genders were group-housed seprtely both during the post-wening period (from 28 to 62 d of ge) nd during the fttening period. Cre nd use of nimls were performed ccording to the certificte of Authoriztion to Experiment on Living Animls, n (delivered by the Ministry of Agriculture to N. Quiniou) Mngement of pigs At 5 dys of ge, only one third of mles were cstrted within ech litter. Bors were llocted to the cstrted group or to the non-cstrted group on the bsis of their birth weight. At wening, ll nimls were moved to post-wening unit nd group-housed seprtely (8 or 9 pigs/pen). Animls were llotted in the pens on the bsis of their sex, their dm, nd their BW t wening. At 62 d of ge, 30 pigs per gender were moved to one fttening room nd group-housed seprtely (6 pigs/pen). Five replictions of three pens were prepred. Within ech repliction, pigs were chosen in order to get 1

2 littermtes, or hlf- brothers/sisters ccording to the sire, of the three genders in the pens nd n verge initil BW per pen similr for the three genders. The pigs were fed d libitum until slughter. All pigs were slughtered on the sme dy Housing nd feeding conditions All pigs were bred in dynmic ventilted fttening rooms on totl sltted, concrete floor. The spce llownce ws 0.35 nd 0.65 m²/pig during post-wening nd fttening periods, respectively. Pigs hd free ccess to wter nd to pelleted dry diet in double spce feed dispenser. During the postwening period, pigs were fed with commercil diet. During the fttening period, single diet ws used, which net energy (NE) content ws 9.7 MJ/kg. Its stndrdized digestible lysine (LYSd) content to NE rtio ws fixed t 0.89 g/mj nd other digestible mino cids to LYSd rtio were djusted ccording to the idel protein concept, i.e. 30% for methionine, 60% for methionine + cystine, 65% for threonine nd 19% for tryptophn (Tble 1) Mesurements The pigs were individully weighed t wening (28 d of ge), the dy before the end of the post-wening period (62 d) fter 16-h feed deprivtion, t 21-d intervls until 100 kg nd therefter t 7-d intervls until slughter fter 6-h fsting to clculte the verge dily gin (ADG) over different periods. The feed intke per pen ws recorded between ech weighing nd used to clculte the verge dily feed intke (ADFI) nd the feed conversion rtio (FCR). In cse of deth or ny other problem, the pig removed from pen ws weighed. When the expected slughter weight (minimum 110 kg BW) ws chieved, the pigs were fsted t 8:00, weighed t 14:00 nd trnsported 87 km to commercil slughter house t 17:00. They were ll slughtered t 8:00 on the next dy fter 24-h without ny ccess to diet but n d libitum ccess to wter nd 15-h rest period before slughter. Pigs were stunned with CO 2, exsnguinted nd eviscerted. The hot crcss ws weighed; it corresponded to both hlf-crcsses with feet nd hed but without the kidney ft nd the tongue. The crcss len met content ws estimted from the bckft depth mesured between the 3 rd nd 4 th lst ribs (F34) nd the Longissimus dorsi muscle depth between the 3 rd nd 4 th lst ribs (M34) obtined with CGM invsive probe (Sydel, Lorient, Frnce). Pig behviour ws recorded during the fttening period using simplified nd instntneous scn smpling technique. When the observer rrived in the room t 15:00, pigs were encourged to stnd nd move. Observtions strted ten minutes lter. Ech pig inside ech pen ws observed 5 times, every 2-min. A first scn ws performed on ech pen nd therefter second scn ws performed gin on ech pen. The ethogrm consisted of gonistic/positive behviour, mounting, investigtion nd resting. No distinction ws mde between other behviours. On the dy following these observtions, the pigs were inspected for lesions using protocol similr to tht developed in the welfre ssessment tool Welfre Qulity (2009). Lmeness nd lesions were ctegorised s described in Tble 2. The skin lesions were counted for ech niml on different body res: er, front, flnks, hind-qurters nd legs, on both sides of the pig. The cumulted score corresponded to the sum of skin lesions observed pondered with coefficient (Tble 2). The observtion sessions were repeted four times: 3, 6, 9 nd 11 weeks fter the rrivl in the fttening room. Ingredients, g/kg Tble 1. Dietry chrcteristics (s fed). Clculted nutrient composition Whet 586 Moisture, g 133 Brley 150 Crude protein, g 162 Whet brn 30 Crude lysine, g 9.6 Soyben mel Digestible lysine (LYSd), g Rpeseed oil 9.8 Crude fiber, g 33 Cne molsses 20 Ash, g 39 Lysine (50% content) 4.5 Clcium, g 7.3 MHA 0.6 Phosphorus, g 4.8 Threonine 0.9 Digestible phosphorus, g Slt 4 Ether extrct, g 26 Clcium crbonte 10 Digestible energy, MJ Bi clcium phosphte 5.1 Net energy (NE), MJ 9.71 Phytses 0.1 LYSd / NE, g/mj 0.89 Vitmin nd trce minerl mixture 1. Stndrdised idel digestibility. 2. Without endogenous phytses (INRA-AFZ tbles, 2004). Score Lmeness 4 Tble 2: Lesion types nd ssocited severity scores Mening 0 Norml git 1 Abnorml git but still using ll legs 2 Minimum weight bering on one leg 3 Serious lmeness Lesion score 1 Scrtch or smll wound (size under 2 cm) 5 Wound between 2 nd 5 cm 16 Opened wound, size bove 5 cm 1.5. Clcultions nd sttisticl nlyses. Growth performnce were clculted over the whole period, i.e., post-wening or fttening, nd over the growing nd the finishing periods (before/fter 67 kg BW). Individul dt were submitted to multifctoril nlysis of vrince with the gender (G) nd the repliction (R) s the min effects nd the pen s the experimentl unit using the proc MIXED procedure of SAS (1998). A multifctoril nlysis of vrince ws lso performed in order to test the effect of the stge of growth nd its interction with the gender on the growth performnce. Crcss trits were nlysed with the hot crcss weight included in the sttisticl model s covrite. Dt recorded on pen scle were nlysed with G nd R s min effects. Dt were used to ssess the chronologicl increse of the verge body weight (BW) nd of the verge cumulted feed intke from the beginning of the fttening period with ge. These dt were curve-fitted to chrcterise ech gender in terms of BW nd feed intke nd used to model nutrient requirements using InrPorc softwre. In this growth model, ADG is described through modified Gompertz function (vn Milgen et l., 2008), of which prmeters re the expected BW 2

3 t 63 dys of ge (BW63d), the ge t which pigs rech 110 kg (ge110) nd shpe prmeter (BGompertz) tht describes the precocity of pigs (Brossrd et l., 2009) (Eqution below). The feed intke ws described s power function of BW. A clibrtion procedure ws used tht estimted sttisticlly the model prmeters of both growth nd intke curves using lgorithms provided by TPMth softwre. BW(Age)= ( )^ BW63 ( BGompertz (Age110 63)) ( BGompert (AGE 63)) { e e } ( 1+ e ( BGompertz (Age110 63)) ) performed per pen nd per stge, fter log-trnsformtion. An nlysis of vrince ws performed with the sex nd the stge of mesurement s min effects nd the pen s rndom effect (proc MIXED, SAS 1998)., Vribles tht were not normlly distributed nd lesion scores were nlysed using Kruskll-Wllis test. As fr s seldom behviour ws concerned, ll the observtions performed t the four stges of observtion were gthered in order to quntify the sex effect. Within ech stge, bursitis, til sttus nd lmeness frequencies were nlysed using Fisher's test. For til sttus, the clsses 1 nd 2 were combined. Similrly for lmeness, the clsses 2 nd 3 were combined. The vribles used to describe the different components of the behviour were expressed s percentge of the observtions Tble 3: Effect of the gender on growth performnce in Exp. 1 nd Exp. 2. Physiologicl stge Post-wening Growing-finishing Gender 1 Brrow Mle Gilt RSD Sttistics 1 Brrow Mle Gilt RSD Sttistics 1 Individul dt 2 Observtions, No Body weight, kg At28 d of ge At 43 d of ge At 63 d of ge At 105 d of ge b 67 b 2 G*** At 152 d of ge b b 7.4 G*** ADG, g/d b 75 G*** First hlf b 979 b G*** 99 Second hlf b 995 G P*** Results on pen bsis Observtions, No ADFI, kg/d b 2.45 b 0.07 G*** First hlf b G** 0.07 Second hlf b 2.82 b P*** FCR, kg/kg b 2.48 c 0.03 G*** First hlf G b G** Second hlf b 2.84 c P***, G P Gender: B= brrows, M= mles or bors, G= gilts. 2. Model 1: vrince nlysis with the gender (G) nd the repliction (R) s the min effects, nd the pen s the experimentl unit. Within row, mens without common superscript differ (P < 0.05). 3. During the post-wening period: first hlf =28-42 d, second hlf=43-63 d; during the fttening period: first hlf= d, second hlf= d. 4. Model 2: split plot nlysis of vrince with the gender, the repliction, the physiologicl sttus nd interctions s the min effects nd the pen considered s the experimentl unit. 2. RESULTS 2.1. Post-wening period The ADG ws not significntly influenced by the gender, whichever the period considered (). Despite lower vlues of ADFI nd G:F obtined in bors, the difference ws not significnt with those obtined in brrows nd gilts Fttening period Growth performnce. The ADG ws significntly influenced by the gender. The lowest growth rte ws observed in gilts ll long the fttening period. At slughter, they were subsequently lighter (113 kg) thn other genders (119 kg on verge). No difference on ADG ws induced by cstrtion over the totl fttening period. Yet, significnt interction between the gender nd the stge of growth ws observed (P<0.001). Indeed, brrow ADG ws significntly higher during the growing period, wheres the opposite ws observed during the fttening period. The ADFI ws 11% lower in mles when compred to brrows, wheres no difference ws observed between bors nd gilts (2.43 kg/d on verge). The G:F rtio ws significntly ffected by the gender. Tking into ccount differences observed on both ADG nd ADFI, the G:F of gilts ws intermedite between those of cstrted or entire mles. Crcss trits. A lower crcss yield ws obtined in bors (78.6%) thn in brrows nd gilts (79.9% on verge). Even if the BW of bors ws 4 kg hevier t slughter, the difference between their crcss weight nd those of gilts nd brrows ws only 1 kg. The bckft thickness mesured t slughter ws lower in bors nd gilts thn in brrows (Tble 3), wheres the muscle thickness ws not significntly influenced by the gender. Such results would be consistent with reduced crcss ftness in entire mles when compred to cstrted ones. 3

4 Tble 4: Effect of the gender on crcss chrcteristics Gender 1 B M G RSD Sttistics 1 Observtions, No Crcss weight, kg b 6 G* 2 Crcss yield, % b G***, W*** G34, mm b 15 b 3 G***, W*** M34, mm G 0.07, W* Len content, % See Tble The wrm crcss weight ws introduced in Model 1 s covrite. Growth profile. Averge BW nd cumulted feed intke from the beginning of the tril were used to chrcterise the growth nd feed intke curves for ech gender. From dt indicted in Tble 5, were used to clibrte Gompertz function nd power functions, respectively. The corresponding prmeters (Tble 6) were used in the InrPorc softwre in order to ssess the nutritionl requirements for the three genders. The evolution of the LYSd requirement per MJ NE with BW is illustrted in Figure 1. Tble 5: Evolution of BW nd feed intke with ge. Gender Age (d) BW (kg) ADFI, g/d Feed intke, g cumulted, g Bors Gilts Brrows Behviour. Whtever the stge of growth considered, the brrows hd lower level of ctivity thn bors nd gilts. Even if bors exhibited more socil behviour nd gilts more explortion, no significnt difference between genders ws obtined on this type of ctivity. No mounting behviour ws observed in brrows. This behviour ws minly observed in bors but lso in gilts (P<0.05). Mounting behviour ws observed during the four observtion sessions but its frequency ws rther vrible (1.4, 0.6, 1.4 nd 0.8% during sessions performed on week 3, 6, 9 nd 11, P>0.10). Figure 1: Evolution of the digestible lysine requirement (g/mj NE) with BW for the three genders, using InrPorc softwre. Tble 6: Growth curve prmeters. Gender B M G Growth curve 1 Initil ge, d BW t initil ge, kg Age t 110 kg, d Bgompertz Protein deposition, g/d Intke curve:.pv b, g b Gompertz model. 2. Averge vlue over the BW rnge considered. Tble 7: Frequency of the different behviours (%). Gender B M G RSD Stt. Observtions, No Pens, No Socil behviour G 0.08 S 0.06 Positive G 0.07 S* Negtive Mount b 0.2 b G* Investigtion b 27.0 b 7.0 G** S** Resting b 25.0 b G** Others Vrince nlysis with the gender (G) nd the observtion session S s min effects. 2. Kruskl Wllis test. Body condition. Lesions were scored t higher level in bors thn in brrows nd gilts (31.5 vs nd 24.1, respectively). The difference between genders ws significnt on weeks 3 nd 6, but not on weeks 9 nd 11 (Figure 2). During the tril, the vrition of lesion scores with time depended on the gender. It ws significntly higher in brrows on week 3 thn fterwrds. In contrst, lesion scores remined reltively constnt in gilts. In bors, lesions were more frequent (P<0.05) on weeks 3 nd 6 (40 nd 36, respectively) thn on weeks 9 nd 11 (26 nd 24, respectively). 4

5 Score b b Brrow Cstrt Mle Mâle Femle Femelle Semine Week Figure 2 : Evolution of the verge skin lesion score during the fttening period in the three genders. Tble 8: Effect of the gender on body condition scored (% pigs per score). Gender B M G Stt. 1 Observtions, No Bursitis, % 2 Score Score Score Til biting, % 2 Score Scores 1 nd Lmeness, % (week 11) Score 0 70 Score b 7 b 97 Scores 2 nd Fisher's test. 2. Frequencies clculted from ll observtions performed. 90 ns S 0.10 The frequency of socil behviour incresed over time from 17% on week 3 to 22% on weeks 6, 9 nd 11 (P<0.05). Simultneously, less explortion of the pen ws observed during the second hlf of the fttening period (27% on weeks 3 nd 6 vs 21% on weeks 9 nd 11, P<0.01). The verge score obtined for bursitis ws not significntly different between genders, even if the score 1 ws more frequently obtined in brrows, whtever the week considered. The scores 1 nd 2 used for til biting were gthered s this lter nottion occurred only for one bor. Intct tils were more often observed in gilts thn in entire nd cstrted mles, but the difference ws not significnt. No effect of the gender ws observed on the lmeness frequency on weeks 3, 6 nd 9. On the opposite, t the end of the fttening period (week 11), more leg wekness (score 1 nd 2) were observed in brrows thn in bors, frequency in gilts being intermedite (P<0.05). 3. DISCUSSION Cstrtion induced n increse of both ADFI nd FCR, which is in greement with literture dt. In our study, the ADFI nd the FCR were 12 nd 16% higher, respectively, in brrows thn in bors. Such vlues re intermedite between the strongest nd the wekest consequences of cstrtion reported in literture either from different breeds or over different BW S* rnges. When only dt obtined over similr BW re considered, it ppers tht the ADFI increment in brrows is less importnt wheres the FCR increment is more importnt in our study (Figure 3). Indeed, ccording to Xue et l. (1995), Zeng et l. (2002) nd Puly et l. (2008), cstrtion ws ssocited with n incresed ADFI nd with n incresed ADG, while no difference of ADG ws observed in our tril. An incresed difference of FCR in our study would be consistent with much more importnt difference of body ftness in the present tril when compred to literture. Yet, it is difficult to compre the effect of cstrtion on crcss lenness obtined in the previous studies s len content ws not mesured but ssessed from indirect clcultions. However, everyone greed bout the higher body ftness of brrows. The ADFI of mles ws close to tht of gilts, in greement with Hnsen nd Lewis (1993) nd Noblet et l. (1994). In contrst, the gilts presented slightly lower ADG, hence higher FCR. With regrd to these differences, gilt crcss lenness should be intermedite between brrows nd bors (Hnsen nd Lewis, 1993; Noblet et l., 1994). Indeed, ccording to our dt, the bckft thickness ws numericlly higher in gilts thn in bors, but the difference ws not significnt. A lower crcss yield in bors ws lredy reported by Hnsen nd Lewis (1993), Noblet et l. (1994), Quiniou et l. (1996) nd Zeng et l. (2002). This result ws explined by the contribution of offls, especilly the reproductive trct, to BW t slughter (Quiniou nd Noblet, 1995). Different LYSd requirement were estimted for the three genders, in greement with Noblet nd Quiniou (1999). Over the fttening period, the LYSd requirement per unit of NE intke decreses with incresed BW, but it remins higher ll over the BW rnge ( kg) for mles thn for brrows nd gilts. During the growing period, similr LYSd ws simulted for brrows nd gilts, which is consistent with the similr FCR obtined for these genders. On the opposite, during the finishing period, the LYSd requirement decresed more rpidly for brrows thn for gilts, resulting from the incresed ftness of body gin nd FCR in brrows over this BW rnge (Noblet et l., 1994). As illustrted in Figure 1, the bor LYSd requirement would be higher thn the LYSd/NE content in the diet supplied during the tril (0.89 g/mj). According to Quiniou et l. (2009), shortge of mino cid over short period of time t the beginning of the growing period, followed by mino cid supplies in excess, did not influence the overll performnce obtined until slughter. Yet, this deficiency might explin the significnt interction between the gender nd the physiologicl stge (Tble 3). Results obtined with the instntneous nd simplified method to describe the behviours performed by the pigs when they re ctive re consistent with those obtined through continuous observtions over longer period (Courbouly et l., 2008). A lower frequency ws obtined for resting behviour thn in literture, due to the method used; however it differed significntly mongst genders. After the disturbnce tht occurred before the beginning of the observtion sessions, the level of ctivity remined high over longer durtion for mles nd gilts thn for brrows. It ws ssocited with more frequent socil behviour performed by these two genders, especilly towrd negtive behviour for mles. Giersing et l. (2006) reported much more mrked gonistic behviour in mles thn in brrows nd gilts. 5

6 Figure 3 : A review of difference of growth performnce between genders (bse 100: mle) from literture dt obtined over BW rnge close to BW rnge in the present study ( ). Mounting behviour ws minly observed on mles, but lso sometimes in gilts. Mount ws performed by group-housed mles through out the fttening period, in greement with Boyle nd Björklund (2007). When mles were mixed with gilts, these uthors observed decresed frequency of mounting behviour. The higher frequency of socil behviour ws ssocited with higher lesion score in mles thn in other genders, t lest t the beginning of the fttening period. Aggressiveness decresed with ge ccording to Rydhmer et l. (2006). It took probbly more time for mles to orgnise the hierrchy between pen-mtes thn for brrows nd gilts. But, s soon s the hierrchy ws estblished, the lesion score remined stble, in greement with previous observtions performed on gilts nd brrows by Courbouly (2005). Til lesions were twice more frequent in brrows nd mles thn in gilts. This result is in greement with EFSA (2007), who reported significnt effect of the gender on til biting. No effect of cstrtion ws observed on this lesion. More frequent gonistic nd mounting behviours were expected to be ssocited with incresed leg wekness (Rydhmer et l., 2006). However, from weeks 3 to 9, no significnt effect of the gender ws observed on lmeness occurrence. During the lst observtion session, no problem ws observed in mles, wheres 10% of brrows exhibited lmeness. Lmeness is often ssocited with high ADG nd high crcss lenness (EFSA, 2007b). Yet, even if the AGD ws similr over ll the growth period, higher ADG were observed for brrows during the growing phse. An intensive growth t the beginning of the fttening period my hve contributed to lter leg qulity. Then, it would explin the leg wekness in brrows t the end of the fttening period, even when they performed no mounting ctivity. More leg problems were lso ssocited with more bursitis scored 2 in brrows. CONCLUSION The present study ws crried out in order to bring up-to-dte dt on growth performnce of brrows, mles nd gilts nd to obtin new informtion bout their behviour nd body condition when group-housed in smll pens nd fed d libitum. Additionl experiments need to be run in order to get informtion under other housing nd feeding conditions, in other words in the vrious on field breeding conditions. According to differences observed on growth performnce, the dietry mino cid level should be incresed in order to meet the mle requirement. The digestible lysine by MJ of net energy intke should increse by round +0.1 g, but other mino cids s well in greement with the idel protein concept. However, higher dietry nutrient content will result in more expensive feed cost per pig, nd it will be performed only under context of chep feedstuffs nd of good pyment of crcsses. No mjor effect of cstrtion ws observed on the behviour nd body condition. However, solutions hve to be proposed in order to reduce gonistic behviours nd lesions fter mixing t the beginning of the fttening period. Further experiments re necessry to explore the behviour of mle pigs when they re older t slughter or when mles from one given pen re not slughtered on the sme dy. ACKOWLEDGEMENTS INAPORC nd the "Progrmme Ntionl de Développement Agricole et Rurl" re grtefully cknowledged for their finncil support. The uthors grtefully cknowledge the ssistnce of the IFIP technicins nd stockmen t the experimentl sttion for their contribution to the study. 6

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