Camp Montoro et al. Porcine Health Management (2021) 7:7 https://doi.org/10.1186/s40813-020-00187-7 RESEARCH Open Access Effect of space allowance and mixing on growth performance and body lesions of grower-finisher pigs in pens with a single wet-dry feeder Jordi Camp Montoro1,2* , Laura Ann Boyle1, David Solà-Oriol2, Ramon Muns3, Josep Gasa2 and Edgar Garcia Manzanilla1,4 Abstract Background: Low space allowance (SA) and mixing may result in reduced growth performance (GP) and animal welfare issues because of adverse social behaviours directed to pen mates. This could be exacerbated in pens with single space feeders owing to social facilitation of feeding behaviour. The present study aimed to investigate the effect of SA and mixing on GP and body lesions (BL) in pens with one single space wet-dry feeder. Results: Two experiments were conducted on grower-finisher pigs from 10 to 21 weeks of age. In Exp1, pigs (N = 216) were assigned to three SA; 0.96 m2/pig (n = 6 pens; 10 pigs/pen; SA96), 0.84 m2/pig (n = 6; 12 pigs/pen; SA84) and 0.72 m2/pig (n = 6; 14 pigs/pen; SA72), in a randomized design. In Exp2, pigs (N = 230) were used in a 2 × 2 factorial randomized design considering SA and mixing as treatments. Pigs were assigned to two SA; 0.96 m2/pig (n = 10 pens; 10 pigs/pen; SA96) and 0.78 m2/pig (n = 10; 13 pigs/pen; SA78) and were either mixed or not at the entry to the finishing facility. GP was not affected by SA (P > 0.05) in either experiment. In Exp2, non-mixed pigs were 5.4 kg heavier (P < 0.001), gained 74 g more per day (P = 0.004), consumed 101.8 g more of feed per day (P = 0.007) and tended to have higher feed efficiency (P = 0.079) than mixed pigs from 11 to 21 weeks of age. Number of BL was affected by SA in both experiments. In Exp1, SA72 pigs had 74.4 and 97.4% more BL than SA96 and SA84 pigs at 20 weeks of age respectively (P < 0.01). In Exp2, SA78 pigs had 48.6, 43.6 and 101.3% more BL than SA96 pigs at 12, 16 and 21 weeks of age respectively (P < 0.05). Mixing did not affect the number of BL from 12 to 21 weeks of age in Exp2 (P > 0.05). Conclusion: Mixing had a considerable effect on growth performance thus, strategies to avoid or mitigate mixing should be considered. Although space allowance had no effect on growth performance, high number of body lesions in the lower space allowance indicates that space allowances equal or below 0.78 m2/pig are detrimental to the welfare of pigs despite following the EU legislation. Keywords: Animal welfare, Group size, Pig, Regrouping, Stocking density, Swine * Correspondence: jordi.montoro@teagasc.ie 1 Pig Development Department, Animal and Grassland Research and Innovation Centre, Teagasc, Moorepark, Fermoy, Co. Cork P61 C996, Ireland 2 Department of Animal and Food Sciences, Animal Nutrition and Welfare Service, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain Full list of author information is available at the end of the article © The Author(s). 2021 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Camp Montoro et al. Porcine Health Management (2021) 7:7 Page 2 of 8 Background reducing average daily gain (ADG) and average daily One of the greatest challenges for pig producers is to feed intake (ADFI) [22, 23] and it also affects animal maximise pig production efficiency and minimise hous- welfare as pigs show severe aggression after re-grouping ing cost, without compromising animal welfare and farm in order to establish a new social hierarchy [17]. Mixing sustainability. Housing costs are the second highest cost is unavoidable in facilities with large groups at the fin- during the grower-finisher period after feed cost [1]. A isher stage [8, 24], or it may also depend on the previous higher number of pigs per pen, reduces the housing cost management undertake during the farrowing and nur- per pig as pens are used more efficiently [2]. However, sery period [25]. However, farrow-to-finish commercial for a given pen size, increasing the number of pigs per farms with pens of 10 to 14 pigs per pen at the finishing pen causes a reduction in the space allowance (SA), and stage, could facilitate the maintenance of intact litters either a reduction in feeder space per animal in long from farrowing to slaughter with no mixing. Despite no trough systems or an increase in the ratio of animals per references are available, such a penning arrangement feeder in facilities with an ad libitum feeding arrange- with one single space wet-dry feeder is a common type ment [3]. This may result in a reduction in productive of accommodation for grower-finisher pigs in Europe. performance [4–6]. Changing the number of pigs per Thus, studies optimizing this system for efficiency and pen may induce confounding on whether productive animal health and welfare are needed. performance is affected by SA, feeder space or group Previous literature showed the effects of SA on growth size [7], although this method is the most common ap- performance in grower-finisher pigs [1, 4, 11] but the in- plied in commercial conditions. Nevertheless, recent re- formation on how mixing affects growth performance in search pointed out no effect of group size and feeder grower-finisher pigs is scarce and little attention has space on productive performance [1, 8, 9]. been paid to whether space allowance and mixing inter- Kyriazakis and Whittemore [10] reported a formula act with each other [22, 23]. Understanding how where SA in m2 is expressed as: SA = k × BW0.667 where productive performance is affected by different space al- k represents a space allowance coefficient and BW0.667 lowances and mixing in each system is important for pig represents the geometric conversion of body weight producers, veterinarians and advisors to make better (BW) in kg to area. Gonyou et al. [11] reported that management decisions. In the present study we hypothe- below 0.0336 m2/BW0.667 productive performance is af- sised that an interaction between mixing and SA exists fected. However, these thresholds are likely to change and it affects pig productive performance and animal for each type of building, floor type, feeders, environ- welfare. Therefore, the aim of the present study was to mental enrichment, sex and pig’s genetics [9, 12], and investigate the effect of space allowance and mixing on animal welfare may be compromised before performance growth performance and body lesions, as a proxy for ag- is affected. Space allowance is part of the Welfare Qual- gression, in pens with a single space wet-dry feeder dur- ity assessment of pig production [13] and it is well ing the grower-finisher stage. known that insufficient SA can lead to adverse social be- haviours directed to pen mates, resulting in skin lesions, lameness, and tail biting [14]. These lesions are more Methods sensitive indicators of pig welfare [15] than growth per- Care and use of animals formance. Existing research recognises the critical role Two experiments (Exp1 and Exp2) were conducted at played by space allowance [7, 14, 16] and mixing [17] on the Teagasc Pig Research Facility in Fermoy, Co. Cork, the number of body lesions per pig as an indicator of Ireland. Both experiments received ethical approval from poor animal welfare. The physical damage induced by the Teagasc Animal Ethics Committee (TAEC 204/ aggression may end affecting pig performance causing 2018). Danish Duroc × (Large White × Landrace) carcass condemnations and economic losses for pig pro- grower-finisher pigs were housed in mixed sex pens with ducers [18]. Moreover, damaging behaviour may con- fully slatted concrete floor (2.4 × 4.2 m) containing a sin- tribute to chronic stress which affects both mental and gle wet-dry feeder (330 mm [Width] × 370 mm [Depth] × physiologic natural state of the animals [19], thereby 1000 mm [Height]; MA37, Verba, Netherlands) and one having detrimental implications to the efficiency and supplementary nipple drinker. Water and pelleted feed sustainability of swine production systems [20]. were provided ad libitum. Temperature was controlled Mixing is a common strategy used in pig production by a mechanical ventilation system with fan speed and to sort pigs by weight to reduce variability and facilitate air inlet area regulated by a climate controller. Pens were management in the grower-finisher stage, even though it enriched with a larch wood post. Pigs were fed a single has minimal impact on the final variability in individual soybean meal-maize-wheat based finisher diet (16.2% pig weights within a pen [7, 21]. In fact, there are indica- Crude Protein, 9.7 MJ per Net Energy and 0.92% Stand- tions that mixing affects productive performance by ard Ileal Digestible Lysine per kg of feed) and remained Camp Montoro et al. Porcine Health Management (2021) 7:7 Page 3 of 8 in the facility until the first group of pigs reached 110 kg kg of feed consumed BW gain for each 2-week period. of BW and were sent to slaughter in both experiments. In Exp1, a total of 216 pigs were used and moved as Pen efficiency intact litter pens to the finisher accommodation at 10 weeks of age (26.3 ± 2.26 kg BW). Pigs were assigned per Overall pen efficiency was calculated for each treatment pen to three different SA; 0.96 m2/pig (10 pigs/pen; n = in both Exp1 and Exp2. Pen efficiency was calculated as kg daily gain 6; SA96), 0.84 m2/pig (12 pigs/pen; n = 6; SA84) and sq m space . 0.72 m2/pig (14 pigs/pen; n = 6; SA72), in a randomized design. Litter pens were adjusted to the SA treatments Body lesion counts by removing pigs in case it was necessary. All SA were Following the Welfare Quality® criteria [13], the body of above the minimum space per pig set by European legis- the pigs was divided into anterior, mid and posterior lation based on live weight [26]. part. Body lesion was defined as either surface penetra- In Exp2, a total of 230 pigs were used in a 2 × 2 factor- tion of the epidermis or penetration of the muscle tissue ial randomized design considering SA and mixing as [13]. Then, all skin lesions in each location were counted treatments. Pigs were moved to the finisher accommoda- individually as body lesions and recorded on a check tion at 11 weeks of age (34.3 ± 3.25 kg BW). Pigs were sheet [13]. In Exp1, body lesions were counted at 20 assigned to two different SA; 0.96 m2/pig (n = 10 pens; weeks of age before pigs started to go to slaughter. In 10 pigs/pen; SA96) and 0.78 m2/pig (n = 10 pens; 13 Exp2, body lesions were counted at 12, 16 and 21 weeks pigs/pen; SA78), all above the minimum space per pig of age. set by European legislation based on live weight [26]. Mixing was applied randomly to 5 pens of each SA while Statistical analyses the rest of the pens remained as litter pens. Litter pens All data were analysed using SAS v9.4 (SAS Institute were adjusted to the SA treatments by removing pigs in Inc., Cary, NC, USA). Each pen was considered as the case it was necessary. experimental unit for all data analyses. In Exp1, the In both experiments, space allowances were adjusted models included SA as fixed effects. In Exp2, models in- by changing the number of pigs per pen as it would hap- cluded SA, mixing and their interaction as fixed effects. pen in field conditions. Space allowance coefficient (k) Models for BW, ADG, ADFI, FCR and pen efficiency for each treatment were calculated using the formula were analysed using general linear mixed model ac- SA = k × BW0.667 [10] and are reported in Table 1. counting for repeated measurements in both experi- ments. Initial BW was used as a covariable for BW, ADG, ADFI and FCR. Body lesions were analysed using Measurements a generalized linear mixed model in both experiments. Body weight, feed intake and feed efficiency traits Difference between treatment groups on body lesions In both experiments, pigs were weighed per pen and A − Group B BW was recorded every two weeks until the first group were calculated as GroupGroup B . Multiple means com- of pigs reached 110 kg of BW and were sent to slaughter. parisons were done using Tukey-Kramer’s correction in Average daily gain was calculated for every 2 weeks all cases. Alpha level for determination of significance interval. Feed intake was recorded daily at a pen level, was 0.05 and trends were identified as alpha of 0.10. Re- added for every 2 week period and ADFI was calculated. sults for fixed effects are reported as least square means Feed conversion ratio (FCR) was calculated as ± standard error mean. Table 1 Initial and final space allowance coefficient (k) for each Results treatment in experiment 1 and 2 Body weight, feed intake and feed efficiency traits Experiment 1 Experiment 2 Final BW, ADG, ADFI and FCR from 10 to 20 weeks of Number of pigs/pen 10 12 14 10 13 age, were not affected by SA in Exp1 (P > 0.05; Table 2); Space allowance, m2/pig 0.96 0.84 0.72 0.96 0.78 although SA96 pigs were numerically heavier and had Space allowance coefficient, k a lower FCR than SA84 and SA72 pigs by the end of the Initial b 0.110 0.095 0.079 0.090 0.074 trial. Final 0.042 0.037 0.031 0.042 0.034 BW showed an interaction between SA and mixing in Exp2. SA78 non-mixed pigs were 6.1 and 6.5 kg heavier a The allometric expression of the space coefficient is as follows: κ = Space allowance (m2) / BW0.667 (kg) than SA96 and SA78 mixed pigs at 21 weeks of age b Initial body weight in experiment 1 was: 25.6 ± 1.38 kg (0.96 m2/pig), (P < 0.001; Table 3). This interaction was not present 26.1 ± 1.38 kg (0.84 m2/pig) and 27.4 ± 1.38 kg (0.72 m2/pig). Initial body weight in experiment 2 was: 34.6 ± 0.95 kg (0.96 m2/pig) and for ADG, ADFI or FCR. Non-mixed pigs gained 74 g 34.1 ± 0.95 kg (0.78 m2/pig) more per day (P = 0.004) and consumed 101.8 g more of Camp Montoro et al. Porcine Health Management (2021) 7:7 Page 4 of 8 Table 2 Effect of space allowance on productive performance feed per day (P = 0.007) than mixed pigs from 11 up to and body lesion counts in Exp11 21 weeks of age (Table 3). Non-mixed pigs tended to Trait Space Allowance, m2/pig 2 P-value have lower FCR compared to mixed pigs from 11 to 21 0.96 0.84 0.72 SEM weeks of age (P = 0.079; Table 3). BW, kg, 20 wk 103.5 100.6 99.8 1.38 0.162 ADG, g 1211.8 1155.0 1141.0 35.88 0.396 Pen efficiency Pen efficiency increased by reducing SA during the ADFI, g 2566.2 2558.9 2580.2 70.34 0.979 grower-finisher period in both experiments (P < 0.001). FCR 2.15 2.20 2.26 0.07 0.578 SA72 pigs had higher overall pen efficiency compared to 3 Body lesions , 20 wk SA96 and SA84 pigs in Exp1 (P < 0.001; Fig. 1). More- b Anterior 2.0 2.3 b 4.1 a 0.40 < 0.001 over, in Exp2, SA78 non-mixed pigs had higher overall Mid 1.0 1.0 1.6 0.26 0.263 pen efficiency than SA78 mixed pigs (P = 0.049) and Posterior 0.8 b 1.1 ab 1.7 a 0.23 0.021 SA96 non-mixed and mixed pigs (P < 0.001; Fig. 2). Also, b SA78 mixed pigs had higher overall pen efficiency than Total 3.8 4.3 b 7.5 a 0.78 0.003 1 SA96 non-mixed and mixed pigs (P < 0.05; Fig. 2). Body weight (BW), average daily gain (ADG), average daily feed intake (ADFI), feed conversion ratio (FCR) and body lesion counts from 216 grower-finisher pigs (6 pens/treatment; Least square means ± Standard error mean [SEM]) Body lesion counts from 10 to 20 weeks of age, when the first group of pigs reached 110 kg of Body lesion counts were higher at the lower SA at 20 BW and were sent to slaughter 2 0.96 m2/pig = 10 pigs/pen; 0.84 m2/pig = 12 pigs/pen; weeks of age in Exp1 (Table 2). SA72 pigs had 78.3 and 0.72 m2/pig = 14 pigs/pen 105.0% more lesions than SA84 and SA96 pigs on the 3 Mean of the total number of body lesions counted at anterior, mid, posterior and total body regions on both sides of the body anterior body region respectively (P < 0.001). There was a,b Within rows, significant differences between groups (P < 0.05) no difference in counts on the mid body region between SA (P > 0.05). On the posterior body region, SA72 pigs Table 3 Effect of space allowance × mixing on productive performance and body lesion counts in Exp21 2 Space Allowance 2 0.96 m /pig 0.78 m2/pig P-value Trait Mixed Non-Mixed Mixed Non-Mixed SEM Mixing Space Allowance Interaction b ab b a BW, kg, 21 wk 102.1 106.4 101.7 108.2 0.95 < 0.001 0.472 < 0.001 ADG, g 983.0 1034.1 955.4 1052.3 21.82 0.004 0.836 0.309 ADFI, g 2150.3 2222.3 2125.6 2257.1 32.57 0.007 0.880 0.374 FCR 2.18 2.12 2.19 2.11 0.04 0.079 0.974 0.692 Body lesions 3, 12 wk Anterior 4.2 4.0 6.8 7.3 0.70 0.960 < 0.001 0.622 Mid 2.2 2.3 2.7 2.5 0.47 0.903 0.457 0.777 Posterior 1.0 0.7 1.1 1.1 0.28 0.590 0.371 0.505 Total 7.6 7.0 10.8 10.9 1.23 0.828 0.004 0.748 Body lesions, 16 wk Anterior 3.8 3.7 5.6 5.3 0.71 0.801 0.019 0.894 Mid 1.8 3.0 3.6 3.4 0.56 0.210 0.038 0.119 Posterior 2.2 1.9 2.9 2.8 0.36 0.600 0.021 0.641 Total 7.7 8.6 12.0 11.4 1.51 0.886 0.018 0.598 Body lesions, 21 wk Anterior 2.6 2.0 4.2 4.0 0.59 0.380 0.002 0.497 Mid 0.8 1.0 2.3 1.8 0.39 0.983 0.003 0.410 Posterior 0.6 1.0 2.0 1.8 0.36 0.569 0.001 0.316 Total 4.1 3.9 8.6 7.5 1.21 0.622 < 0.001 0.834 1 Body weight (BW), average daily gain (ADG), average daily feed intake (ADFI), feed conversion ratio (FCR) and body lesion counts (Least square means ± Standard error mean [SEM]) from 230 grower-finisher pigs in 20 pens grouped by space allowance × mixing from 11 up to 21 weeks of age, when the first group of pigs reached 110 kg of BW and were sent to slaughter 2 0.96 m2/pig = 10 pigs/pen; 0.78 m2/pig = 13 pigs/pen 3 Mean of the total number of body lesions counted at anterior, mid, posterior and total body regions on both sides of the body a,b Within rows, significant differences between groups (P < 0.05) Camp Montoro et al. Porcine Health Management (2021) 7:7 Page 5 of 8 anterior, mid and posterior body region respectively at 21 weeks of age (P < 0.01). In total, SA78 pigs had 101.3% more lesions than SA96 pigs at the end of the trial (P < 0.001). Body lesion counts decreased from 16 to 21 weeks of age in all treatments (P < 0.05). Discussion Small group pens with 10–14 grower-finisher pigs are convenient from a management point of view because they allow for a rapid monitoring of health and welfare issues in pigs, without the need to access the pen. This pen system is normally linked to wet-dry feeders as these optimize feed efficiency [27]. Despite no references are available, the authors’ experience in groups like EUPIG (https://www.eupig.eu/) or the ECPHM suggests that this is one of the most common systems in growing- finishing units in the EU. To understand how space al- Fig. 1 Pen efficiency of the space allowance treatments from 10 to lowance and mixing influence growth performance and 20 weeks of age in Exp1. a, b Significant differences between welfare of pigs in this system, pigs were subjected to treatments (P < 0.05) three space allowances (0.96, 0.84 and 0.72 m2/pig) in a first trial, and two space allowances (0.96 and 0.78 m2/ had 112.5% more lesions than SA96 pigs (P = 0.021), al- pig) combined with mixing in the second trial. These though no differences were observed between SA84 pigs space allowances were chosen above the 0.65 m2/pig and the other groups (P > 0.05). In total, SA72 pigs had minimum set by European legislation based on live 74.4 and 97.4% more lesions than SA84 and SA96 pigs weight [26] which is already criticised from a welfare respectively (P < 0.01). In Exp2 (Table 3), body lesion point of view because of very low amount of shared counts were higher at lower SA, however no mixing and space [28]. The space allowances were adjusted by chan- interaction effect were observed (P > 0.05). SA78 pigs ging the number of pigs per pen as it would be observed had 72% more lesions on the anterior body region (P < in current field situations. This fact could induce con- 0.001) and 48.6% more lesions in total (P = 0.004) than founding on whether growth performance is affected by SA96 pigs at 12 weeks of age. There was no difference in space allowance, feeder space or group size [7]. How- the mid and posterior body region between SA treat- ever, these factors are usually confused in any commer- ments at 12 weeks of age (P > 0.05). At 16 weeks of age, cial conditions. Nevertheless, Schmolke et al. [8] SA78 pigs had 45.3, 45.8, 39.0 and 43.6% more lesions observed no detrimental effect on growth performance than SA96 pigs on the anterior, mid, posterior and total of pigs housed at 10, 20, 40 and 80 pigs per pen with a body region respectively (P < 0.05). SA78 pigs had 78.3, space allowance of 0.76 m2/pig and one single wet-dry 127.8 and 137.5% more lesions than SA96 pigs on the feeder provided for every 10 pigs. Moreover, Flohr et al. Fig. 2 Pen efficiency of the space allowance × mixing treatments from 11 to 21 weeks of age in Exp2. a, b Significant differences between treatments (P < 0.05) Camp Montoro et al. Porcine Health Management (2021) 7:7 Page 6 of 8 [1] also reported no effect of group size on ADG, ADFI reported that when pigs are subjected to multiple con- and FCR in similar conditions to the present study. This current environmental stressors such as high ambient results suggests that group size would not affect pro- temperature, regrouping and low space allowance, the ductive performance in the present study. Restricted final effect over productive performance is additive. feeder space could also impact growth performance [3]. In terms of animal welfare, the current study found Wastell et al. [9] compared group sizes of 20 and 26 pigs that the number of body lesions increased at lower space per pen and did not find any detrimental effect on allowances. This finding is in accordance with previous growth performance with 10 pigs per wet-dry feeder literature which reported a strong relationship between space compared to 13 pigs per wet-dry feeder space con- space allowance and body lesions [7, 14, 16]. Anil et al. sidering a space allowance of 0.65 or 0.78 m2/pig. This [7] stated that animal welfare is enhanced at higher results suggest that feeder space would not affect growth space allowances in terms of postural behaviour, lower performance in the present study. Hence, the present injuries and aggression. Space allowance affected the study discusses space allowance as the main factor to number of body lesions during the whole grower- affect growth performance regarding the pen system finisher period. Nevertheless, the number of body lesions studied. decreases as the pigs get heavier which is in accordance In terms of space allowance, previous studies observed with previous studies [33]. A possible explanation for that decreasing space allowance resulted in a poorer this might be related to the pigs’ experience and ability growth performance in pigs with space allowances of to adapt to their social environment and being in a 0.65 m2/pig and similar slaughter weights [4, 5, 9] or stable group for a long time which benefits the long 0.80 m2/pig when marketed to slaughter weights up to term welfare of the pigs [34, 35]. The present study 138 kg of BW [29]. Overall, all these studies can be com- raises the possibility that there is a threshold between pared using the allometric approach expressing space al- 0.78 and 0.84 m2/pig which an increase in the number of lowance as a coefficient (k) [10]. Gonyou et al. [11] body lesions due to space allowance is observed. Still, stated that the critical k value below which growth the number of body lesions as a proxy for aggression performance is affected as space allowance is further de- may vary because of other factors not controlled in the creased, ranges from 0.0317 to 0.0348 over all data sets present study, and moreover, it could also be related to analysed using a broken-line analysis. In our study, pigs the pen design and the wet-dry feeder space per pig. with 0.72 and 0.78 m2/pig reached the critical k value by One interesting finding was that highest body lesion the end of the trial when the first group of pigs reached counts were seen in the anterior body region which is the marketed weight (i.e. 110 kg of BW) and were sent consistent with fighting for access to the feeder [36]. Sin- to slaughter. Thus, the growth performance of the pigs gle space wet-dry feeders may allow to accommodate a would not be compromised during the grower-finisher high number of pigs per feeder space without having a period if space allowance is established based on the detrimental effect on growth performance [9, 37]. How- critical k value at the marketed weight. ever, López-Vergé et al. [38] observed that pigs allotted Mixing affected growth performance during the whole to more feeder spaces had low body lesion counts and grower-finisher period in Exp2. The drop in ADG and tended to have low BW variability within pen by the end ADFI is consistent with previous literature which ob- of the grower-finisher period. served that mixed pigs had decreased ADG and ADFI The results provided in the present study indicate when they were followed in a 4 week experiment at the that animal welfare may be compromised before beginning of the grower-finisher period [22, 23]. Stookey growth performance is affected. Averós et al. [39] sug- and Gonyou [30] also observed a depressed ADG in gested a critical k value of 0.039 for lying behaviour mixed pigs after being mixed for a 2 week period when with a broken-line analysis. This k value is higher than they had 83 kg of BW. The present study showed that the 0.0336 reported by Gonyou et al. [11] below which mixing causes a severe effect on growth performance in productive performance is affected. High number of currently modern facilities and genetics, and strategies body lesions caused by competition or aggression, are to avoid mixing or mitigate it are an important issue for likely associated with detrimental implications for pig future research [31, 32]. health and performance due to immunosuppression The underlying hypothesis in this study was that space caused by the social stress [40–42]. This fact may be allowance and mixing interact with each other in current exacerbated in farms that have more infectious dis- field situations. The study found that mixing effect on eases in comparison to the farm where the trial was final BW is exacerbated at lower space allowances (i.e. performed, which is free of the main infectious dis- 0.78 m2/pig). However, this interaction did not show up eases. Ultimately, compromised animal welfare has in any of the other variables and should be checked for detrimental implications to the sustainability of the repeatability in further experiments. Hyun et al. [22] swine production system [20]. Camp Montoro et al. Porcine Health Management (2021) 7:7 Page 7 of 8 Mixing pigs leads to agonistic social behaviour mainly SA: Space allowance; SA96: 0.96 m2/pig; SA84: 0.84 m2/pig; SA78: 0.78 m2/pig; within the first 24 h [43]. However, the current study ob- SA72: 0.72 m2/pig served that the number of body lesions due to aggression Acknowledgements in mixed groups is the same as the non-mixed groups The authors gratefully acknowledge Joana Cardoso Pessoa, Martyna Lagoda after 1 week of being mixed. This finding is consistent and the Teagasc Pig Research Facility staff for their help on this study. with previous studies which may be explained by the es- Authors’ contributions tablishment of the social hierarchy [44–46]. Neverthe- J.C.M, E.G.M and L.A.B conceived and designed the study. J.C.M collected the less, mixed pigs showed a poor growth performance data. J.C.M and E.G.M analysed the data. J.C.M drafted the manuscript. E.G.M, L.A.B, D.S.O, R. M and J. G reviewed and edited the manuscript. E.G.M compared to their counterparts in the study. This could supervised the study. All authors have read and agreed to the published be related to the social network properties and chronic version of the manuscript. stress that are not shown in body lesions [19, 46, 47]. Regarding pen efficiency, this study supports evidence Funding Jordi Camp Montoro was supported by the Teagasc Walsh Scholarship from previous observations [7] which showed that pigs Scheme grant-in-aid project Introducing new feeding programs and facilities in lower space allowances had higher overall pen effi- for Irish finishing pigs ref. 0415. The funders had no role in the study design, ciency. In addition, pen efficiency showed an interaction data collection and analysis, decision to publish, or preparation of the manuscript. between space allowance and mixing which indicates that pen efficiency in lower space allowance may be af- Availability of data and materials fected when pigs are mixed. These results may encour- The datasets used and analysed during the current study are available from the corresponding author on reasonable request. age pig producers to seek optimal space allowances to optimize overall efficiency and reduce housing costs. Ethics approval and consent to participate Nevertheless, the present study also observed that pig Both experiments from this study received ethical approval from the Teagasc Animal Ethics Committee (TAEC 204/2018). welfare is aggravated in low space allowances. This and if other environmental stressors such as high ambient Consent for publication temperature, mixing or the farm sanitary status are con- Not applicable. sidered, pig performance and pig producer’s income may Competing interests be mitigated even with improved pen efficiency. There- The authors declare that they have no competing interests. fore, further studies considering economic analyses on Author details how environmental stressors affect pig performance and 1 Pig Development Department, Animal and Grassland Research and welfare in different space allowances are needed. Innovation Centre, Teagasc, Moorepark, Fermoy, Co. Cork P61 C996, Ireland. 2 Department of Animal and Food Sciences, Animal Nutrition and Welfare Service, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain. Conclusions 3 Agri-Food and Biosciences Institute, Large Park, Hillsborough, Co Down, This study provides a deeper insight into how space al- Northern Ireland BT 26 6DR, UK. 4UCD Veterinary Sciences Centre, University lowance and mixing affect growth performance and ani- College Dublin, Belfield, Dublin 4 D04 V1W8, Ireland. mal welfare in pens of 10–14 grower-finisher pigs with Received: 26 October 2020 Accepted: 17 December 2020 one single wet-dry feeder. 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