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Tail posture as a detector of tail damage and an early detector of tail biting in finishing pigs
Accepted Manuscript Title: Tail posture as a detector of tail damage and an early detector of tail biting in finishing pigs Authors: Mona Lilian Vestbjerg Larsen, Heidi Mai-Lis Andersen, Lene Juul Pedersen PII: DOI: Reference:
S0168-1591(18)30465-9 https://doi.org/10.1016/j.applanim.2018.08.016 APPLAN 4702
To appear in:
APPLAN
Received date: Revised date: Accepted date:
30-1-2018 6-6-2018 21-8-2018
Please cite this article as: Vestbjerg Larsen ML, Andersen HM-Lis, Pedersen LJ, Tail posture as a detector of tail damage and an early detector of tail biting in finishing pigs, Applied Animal Behaviour Science (2018), https://doi.org/10.1016/j.applanim.2018.08.016 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Tail posture as a detector of tail damage and an early detector of tail biting in finishing pigs
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Mona Lilian Vestbjerg Larsena*, Heidi Mai-Lis Andersenb, Lene Juul Pedersena
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Department of Animal Science, Aarhus University, Blichers Allé 20, 8830 Tjele, Denmark
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* Corresponding author. Tel.: +45 5150 7927.
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E-mail address: [email protected] (M. L. V. Larsen)
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Department of Agroecology, Aarhus University, Blichers Allé 20, 8830 Tjele, Denmark
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A tucked tail worked as a detector of tail damage in finishers Tail posture seemed promising as an early detector of tail biting in finishers Tail posture was affected by risk factors of tail damage
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Highlights
Abstract
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The purpose of the current study was to investigate the relation between the tail posture of finishing pigs and tail damage with the aims to use tail posture as (1) an detector of tail damage, (2) an early detector of
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tail biting to possibly predict and prevent bleeding tail damage. Tails of each individual pig (from 112 finishing pigpens) were scored three times per week for the full study period of 10 weeks. For the first aim,
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tail posture was observed directly in the stable three times per week, just prior to tail scoring, and pigs with a tucked tail were related to their tail scoring. The odds of being scored with a tail wound (both bleeding and non-bleeding) increased by almost sixfold if the pig was also observed with a tucked tail on the same day. More precisely, 28% of the pigs with a tucked tail were also scored with a tail wound, whereas this was only the case for 5% of the pigs with a different tail posture. This relation between a tucked tail and 1
tail damage was larger than previously found in weaners and suggests that a tucked tail could be used as an detector of tail damage, although with the risk of many false identifications of tail damage. For the second aim, tail posture was observed from video the last 3 days prior to bleeding tail damage for case pens (n=20; at least one pig with a bleeding tail wound) and their matched controls (n=20). The number of pigs with
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lowered tails (below the tail root) was observed by scan sampling during 6 h per day. A generally higher probability of having a lowered tail was seen in the case pens compared to the control pens, but the probability of having a lowered tail did not increase prior to bleeding tail damage. Thus, the results indicate that tail posture is a promising early detector of tail biting in finishing pigs, but observations going further back than 3 days from bleeding tail damage are needed to find out when the difference in tail posture arises.
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Alternatively, a less severe definition of tail damage could be used. Further, the differences found were
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relatively small, and thus to be able to predict pens in future risk of tail damage from changes in tail posture
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would probably demand the development of an automatic recording method for the number of lowered tails
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at pen level.
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Keywords: Finishing pigs; Tail posture; Tail damage; Early detection; Straw provision; Stocking density
1. Introduction
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Many pigs raised according to conventional production standards are tail docked due to its preventive effect against tail damage developed from tail biting. Tail biting is an animal welfare problem due to its negative
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consequences, such as experienced stress and pain in the pig (e.g. Munsterhjelm et al., 2013; Valros et al., 2013; Di Giminiani et al., 2017) and the fact that the biter probably performs the tail biting behaviour due to an internal frustration arising from lack of important resources such as lack of proper enrichment to fulfil the exploratory need of the pig (Taylor et al., 2010). However, pigs being tail docked also experience stress and pain during the procedure (Noonan et al., 1994; Herskin et al., 2016) and perhaps in the long term 2
(Simonsen et al., 1991; Herskin et al., 2015). Further, tail docking does not eliminate the occurrence of tail biting or tail damage (e.g. Sutherland et al., 2009; Larsen et al., 2017). Thus, as stated by the EU legislation (EU Council Directive 2008/120/EC), tail docking is only allowed to be performed if injuries to the pigs’ tail occur at the herd and if other preventive measures have been tried first such as improving the
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environment of the pigs. However, allocation of preventive measures may not always be enough to prevent tail damage, especially in undocked pigs (Larsen et al., 2017). Thus, an alternative strategy that could be used simultaneously with the allocation of preventive measures is early detection of tail biting to identify pens in risk of future tail damage. If the farmer was alarmed about pens in high risk of tail damage, then the farmer would be able to make temporary interventions against tail biting that it may not be possible to
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perform for the entire production period. The first step in developing and implementing such a strategy is
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to identify early detectors of tail biting, which for example could be behavioural changes observed prior to
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tail damage. As mentioned, both tail docking and tail biting are painful experiences for the pig. Noonan et
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al. (1994) found that tail-docked pigs tucked their tails between the legs just after the procedure, and they did it more than sham-handled pigs and pigs experiencing other mutilations, such as ear notching or teeth
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clipping. Thus, the experience of tail biting may also cause the pig to lower its tail for example to protect
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the tail from further biting. Larsen et al. (2016) summarised the literature on behavioural changes seen prior to tail damage and identified changes in the tail posture of pigs to be a possible early detector of tail biting
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that deserves more investigation. Only one study has investigated tail posture and its relation to tail biting and tail damage in finishing pigs (from 30 kg until slaughter), and this did not include observations of tail
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posture close in time to the occurrence of tail damage (Statham et al., 2009). This has been investigated in weaners (Zonderland et al., 2009; Lahrmann et al., 2018) and deserves investigation in finishing pigs, as
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the majority of tail damages, definitely in undocked pigs, occur in this phase of the production (Wallgren et al., 2016; Lahrmann et al., 2017). Zonderland et al. (2009) also found a relation between tail posture and tail damage when observed on the same day, which has not been investigated in finishing pigs either. Further, it is unknown whether tail posture and tail damage are directly related due to for example the need to protect the tail or it being the most comfortable posture when injured, or whether they are indirectly 3
related through the relation between tail posture and other stressors leading to tail damage such as lack of enrichment or high stocking density. The current study had three aims: (1) to investigate whether a relation existed for the individual finishing
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pig between tail posture and tail damage when observed on the same day, (2) to investigate whether pen level tail posture in finishing pigs changed prior to bleeding tail damage and whether it differed between pens scored with and not scored with bleeding tail damage and (3) to investigate whether risk factors of tail damage affected pen level tail posture. It was hypothesised that pigs with a tail tucked between the legs would have a higher risk of being simultaneously scored with tail damage, that the number of lowered tails
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would increase prior to bleeding tail damage, and that the number of lowered tails would be higher in the
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pens scored with bleeding tail damage compared to the pens not scored with bleeding tail damage.
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2. Materials and methods
Further information about the study not included here can be found in Larsen et al. (2017). The study was
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no. 2015-15-0201-00593).
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conducted in accordance with a protocol approved by the Danish Animal Experiments Inspectorate (Journal
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2.1 Animals, housing and management
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The experimental unit was 112 finishing pigpens divided between four batches (batch 1, 3, 4: 32 pens each; batch 2: 16 pens). A total of 1624 finishing pigs were included and inserted to the finishing pigunit at an
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average weight of 31.6 ± 6.6 kg at insertion. At insertion, all pigs were checked for damage on the tail, and no pigs with tail damage were included in the study. The finishing pigunit included two rooms (in batch 2, only one room was used), each with 16 identical finishing pigpens. The design and dimensions of the pens can be seen in Figure 1. To include stressors (undocked tails, no straw provided and high stocking density) that potentially would affect the tail posture of the pigs and which are considered risk factors of tail biting
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and tail damage, the pens within each batch were randomly divided between one level of each of three factors: (1) TAIL: pigs with undocked (n=52) or docked tails (n=60), (2) STRAW: not provided with straw (n=56) or provided with 150 g of straw per pig per day on the solid floor (n=56), (3) STOCK: stocking density of 0.73 m2/pig (n=56, 18 pigs per pen) or 1.21 m2/pig (n=56, 11 pigs per pen). Pigs were tail docked
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according to the Danish legislation to half of the tail’s original length with a hot-iron cutter within the first 4 days after birth (BEK nr. 1324). Further, the amount of feeding space per pig was kept approximately equal between the two stocking densities.
2.2 Tail damage – definition and identification
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A pen was recorded as a case pen when at least one pig in the pen was observed with a bleeding tail wound.
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In the following, this day is reffered to as day0 for the respective case pen. After the scoring of the first
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bleeding tail wound in the pen, the pen was no longer included in the study, and pigs with bleeding tail
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wounds were moved to sick pens. Pen level tail scorings were performed daily by the stock personnel from outside the pen, while more detailed tail scorings were conducted each Monday, Wednesday and Friday in
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each of the 10 weeks of the study period after the observation of tail posture (described in section 2.3).
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These detailed tail scorings were performed each scoring day by two observers by entering the pen and scoring each individual tail according to its length, damage and blood freshness if present. Batch 1 included
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five different observers who were all trained according to a scoring protocol with pictures and text, both by group discussions and practical scorings in the stable. Batch 2 included four observers, all of whom were
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also included in batch 1. Batch 3 included five observers of whom one was new and trained by the others. Batch 4 included four observers, of whom one was new and trained by the others. Blinding of observers
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was not possible due to the obviousness of the factors TAIL, STRAW and STOCK.
2.3 Behavioural observations Tail posture was observed both directly in the stable and from video recordings. The direct observations were conducted only in batch 1, 2 and 3 each Monday, Wednesday and Friday in the morning between 0800 5
and 1000 h. This was not conducted in batch 4 due to workload limitations. Thus, these observations were performed on 80 finishing pigpens and for the full study period of 10 weeks per batch. During the observations, the observer entered the pen, woke up the pigs and made sure that all pigs were standing. Afterwards, the observer was standing still in the pen counting the number of pigs with a hangning tail
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posture (the tail is either in a straigt line from the tail root or below the horizontal line from the tail root), number of pigs with the tail tucked between the legs and the total number of pigs in the pen. The identification number of pigs with a tucked tail posture was also recorded. When referring to a lowered tail in the following sections, this is the sum of the number of pigs with the hanging and tucked tail postures. No one, despite the observers, entered the pen or the rooms of the finishing pigunit on that particular day
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before tail posture had been observed. These observations were performed by the same trained observers
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as for tail scoring. Blinding of the observers was not possible due to the obviousness of the factors TAIL,
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STRAW and STOCK. However, tails were scored after the observation of tail posture, and thus the
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observers did not know whether tail damage was present in each pen. Tail posture was observed from video recordings during batch 1, 3 and 4, but only in pens with undocked
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pigs. Batch 2 could not be included, as no matched control pens were available (batch 2 only included four
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pens with undocked pigs due to delivery problems of undocked pigs during this batch). To obtain the video recordings, a camera (Monacor, TYPE-TVCCD-170S, Bremen, Germany) was installed about 3 m above
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the solid floor in each pen, ensuring a full view of the entire pen. These observations were performed the last 3 days prior to day0 (to replicate the method used by Lahrmann et al. (2018)) from 0800-1100 h
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(morning) and from 1530-1830 h (afternoon) by scan sampling every 30 minutes. At each scan, the observer counted the number of standing pigs in the pen and the number of standing pigs with a lowered tail (the tail
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is below the horizontal line from the tail root, also including pigs with a tucked tail posture). The same observations were performed on the same days in one matched control pen per case pen. It was aimed to match case pens to control pens that were from the same batch, had the same combination of TAIL, STRAW and STOCK and that had never been scored with a bleeding tail wound throughout the 10 weeks of the study period. In five cases, the last criteria could not be fulfilled, and these case pens were instead paired 6
with control pens that had not been scored with bleeding tail damage prior to or 1 week after day0. This was accounted for in the statistical analysis and did not affect the results significantly (P>0.05). The video observations were performed by a single trained observer. This observer was not blinded to either the factors TAIL, STRAW and STOCK or whether the pen was a case or control pen. The pens were observed in a
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random order across batches.
2.4 Statistical Analysis
All statistical analyses were performed in R Version 3.2.4. (R Core Team, 2017) using the package ”lme4” (Bates et al., 2015) for generalised linear mixed models. Four models were created, all being logistic
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regression for binomial data using the function “glmer”. All models were reduced according to a 5-%
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significance level (P<0.05). Differences are presented as odds ratios with connected 95% confidence
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intervals (CI).
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2.4.1 A tucked tail as a detector of tail damage in individual pigs (Model 1)
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Model 1 used data on individual pig level from each observation day throughout the study period of 10 weeks or until the pen was recorded as a case pen. Thus, each pen, and thereby pig, had a different number
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of observation days depending on whether and when the pen was recorded as a case pen. A pig could have
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the tail tucked between the legs or not (TP), a bleeding tail wound or not (BTW) and a tail wound (both bleeding and non-bleeding) or not (TWpig), all three as binomial variables. Model 1 tested whether an
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observation of a tail tucked between the legs would increase the odds of finding a tail wound. For this purpose, a model was created including TWpig as a response variable, TP as a main effect and allowed for a random intercept for each pig identification number nested within pen number (1 to 32 within batch 1 and 3; 1 to 16 within batch 2) nested within batch number (1 to 3). It was not possible to make a similar model for the response BTW, as too few pigs were scored with a bleeding tail wound (see Table 1).
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2.4.2 Changes in tail posture prior to bleeding tail damage observed directly in the stable (Model 2) Each case pen was paired with one to three matched control pens depending on the availability within the
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batch. The matched control pens were from the same batch and had the same combination of the factors TAIL, STRAW and STOCK as their respective case pens but were not recorded as case pens throughout the 10-week study period. A pen could be a matched control pen to multiple case pens. A case pen and its matched control pens were observed on the exact same dates prior to the scoring of bleeding tail damage in the case pens (day0). Model 2 used tail posture data from the last 3 observation days prior to day0 (one
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week) obtained through direct observations in the stable. The model included data from 22 case pens and
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31 matched control pens combined in 22 pairs. Prior to analysis, a day category variable (DAY) with three
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levels relative to day0 was created: “day-1 to day-3”, “day-4 to day-5” and “day-6 to day-7”. This was done
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to ensure that all pens were represented in each category, as tail posture was not observed on all days during the week. Furthermore, to account for ongoing tail biting in both the case pens and control pens, a binomial
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non-bleeding tail wound variable (TWpen) was created. TWpen was assigned 1 if the pen had been scored
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with at least one non-bleeding tail wound during the last 3 observation days prior to day0 and 0 if the pen had not been scored with any non-bleeding tail wounds during these days. This was different from being
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scored as a case pen where at least one pig in the pen should have been scored with a bleeding tail wound. The response variable was the proportion of pigs with lowered tails out of the total number of pigs in the
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pen. The model included the main effects pen type (case v. control), DAY, TWpen, period number (1: week 1-3; 2: week 4-6; 3: week 7-10), STRAW, STOCK, TAIL and all two-way interactions between pen type
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and the other main effects DAY, TWpen, TAIL, STRAW and STOCK. Further, a random intercept was allowed for each pen number (1 to 32 within batch 1 and 3; 1 to 16 within batch 2) nested within pair number (1 to 22) nested within batch number (1 to 3). Estimated results from the model are presented as the probability of having a lowered tail in the pen (in percentages).
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2.4.3 Changes in tail posture prior to bleeding tail damage observed from video recordings (Model 3) Model 3 used data observed from video the last 3 days prior to day0. The model included data from 20 pairs
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of case and control pens, all with undocked pigs (thus, TAIL was not included in the model). Here, TW pen was assigned 1 if at least one pig in the pen had been scored with a non-bleeding tail wound during these 3 days and otherwise assigned 0. The response variable was the proportion of pigs with lowered tails out of the number of pigs standing in the pen. The model included the main effects pen type (case v. control), day (day-1 v. day-2 v. day-3), observation period (morning v. afternoon), TWpen, period number (1: week 1-3;
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2: week 4-6; 3: week 7-10), STRAW, STOCK and all two-way interactions between pen type and the main
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effects day, observation period, TWpen, STRAW and STOCK. Further, a random intercept was allowed for
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each pen number (1 to 32) nested within pair number (1 to 22) nested within batch number (1, 3 and 4).
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standing in the pen (in percentages).
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Estimated results from the model are presented as the probability of having a lowered tail among the pigs
2.4.4 Effect of straw provision, stocking density and tail docking on tail posture (Model 4)
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Model 4 used tail posture data observed directly in the stable for the full study period of 10 weeks. As tail damage was expected to affect the tail posture of pigs, this was accounted for by a binomial tail biting
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variable (TB). TB was assigned 1 for the 2 observation days prior to and after a recording of a bleeding tail wound for the specific pen, here termed ‘the days with tail biting’. It was assigned 0 on all other days, here
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termed ‘the days without tail biting’. For case pens, the detailed tail scoring ended after day0 for that specific pen, and afterwards, until the end of the study period, the TB variable was created based solely on the daily tail scorings performed by the stock people from outside the pen. The response variable was the proportion of pigs with lowered tails out of the total number of pigs in the pen. The model included the main effects TAIL, STRAW, STOCK, TB and period number (1: week 1-3; 2: week 4-6; 3: week 7-10) and all two-way 9
interactions between STRAW, STOCK, TAIL and TB. Further, a random intercept was allowed for each pen number (1 to 32 within batch 1 and 3; 1 to 16 within batch 2) nested within batch number (1 to 3).
3.1 A tucked tail as a detector of tail damage in individual pigs
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3. Results
Descriptive results can be seen in Table 1. If pigs were observed not having the tail tucked between the legs, 4.7% and 0.2% of those pigs were later that day scored with a tail wound (both non-bleeding and bleeding tail wounds included) and a bleeding tail wound, respectively. If pigs were observed having the
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tail tucked between the legs, 28.5% and 8.5% of those pigs were later that day observed with a tail wound
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and a bleeding tail wound, respectively. An effect was found of TP (P<0.001) showing that having the tail
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almost sixfold (OR = 5.87, 95% CI [3.92-9.08]).
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tucked between the legs increased the odds of finding a tail wound on the same pig on the same day by
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3.2 Changes in tail posture prior to bleeding tail damage When tail posture was observed directly in the stable (Model 2), only TAIL had a general effect (P<0.01)
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with a higher probability in pens with undocked pigs (6.99%) compared to pens with docked pigs (4.03%; OR = 1.79, 95% CI [1.25-2.58]), irrespective of whether the pen was a case or control pen. The probability
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of having a lowered tail in the pen did not increase prior to bleeding tail damage, neither was it larger in the case pens compared to the control pens. Out of the 22 case pens and 31 control pens included, 19 and 23 of these were scored with at least one non-bleeding tail wound the last 3 observation days prior to day0, respectively, and the majority of these were pens with docked pigs (case pens = 15; control pens = 16).
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When tail posture was observed from video recordings the last 3 days prior to day0 for pens with undocked pigs (Model 3), an effect was found of pen type (P<0.05; OR = 1.60, 95% CI [1.14-2.23]), TWpen (P<0.05; OR = 1.65, 95% CI [1.25-2.52]) and STRAW (P<0.001; OR = 2.41, 95% CI [1.57-3.71]). All three results are illustrated in Figure 2. The probability of having a lowered tail among the pigs standing in the pen did
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not increase prior to bleeding tail damage. Out of the 20 case pens and 20 control pens included, seven and six of these were scored with at least one non-bleeding tail wound the last 3 observation days prior to day0, respectively.
3.3 Effect of straw provision, stocking density and tail docking on tail posture
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For the full study period when tail posture was observed directly in the stable (Model 4), an effect was
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found of STRAW (P<0.001) and STOCK (P<0.001). A higher probability of having a lowered tail was
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seen in pens without straw (3.74%) compared to pens with straw (2.70%; OR = 1.40, 95% CI [1.17-1.67])
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and in pens with high stocking density (5.35%) compared to low stocking density (3.74%; OR = 1.46, 95% CI [1.22-1.74]). Further, a two-way interaction was found between TAIL and TB (P<0.05) with a higher
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probability of having a lowered tail in pens with undocked pigs, both on days with (OR = 2.84, 95% CI
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[2.10-3.82]) and without tail biting (OR = 2.03, 95% CI [1.68-2.44]) and with a higher probability of having a lowered tail on the days with tail biting in pens with undocked pigs (OR = 1.27, 95% CI [1.09-1.49]). The
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result is illustrated in Figure 3.
Discussion
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The odds of being scored with a tail wound (non-bleeding and bleeding) increased when the pig was scored with a tucked tail on the same day. Further, case pens with undocked pigs observed from video recordings showed a higher probability of having a lowered tail compared to the control pens on all 3 days prior to day0. However, the probability of having a lowered tail did not increase prior to bleeding tail damage. The
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probability of having a lowered tail was higher in pens with no straw provision, in pens with the high stocking density and in pens with undocked pigs.
4.1 A tucked tail as an immediate detector of tail damage
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A relation was found between having a tucked tail and tail damage with increased odds of scoring a pig with a tail wound if the same pig was also scored with a tucked tail on the same day. Similar results were found by Zonderland et al. (2009) who studied undocked weaners. They saw that for pigs with a lowered tail, 30% had bite marks or tail wounds (with dried or fresh blood) on the tail, and this was 9% for pigs with a tail tucked between the legs. The current study found an even greater relation between a tucked tail and
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tail damage in finishing pigs with 28% of the pigs with a tucked tail also being scored with a tail wound
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(either bleeding or non-bleeding). However, results from both the current study and the study by Zonderland
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et al. (2009) also clearly demonstrated that using a tucked tail as a detector of tail damage will lead to many
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false identifications and false rejections of tail damage. The current study mostly focused on the lowered tail posture, as only few tucked tails were observed. However, Zonderland et al. (2009) showed that the
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lowered tail compared to the tucked tail as an immediate detector of tail damage will lead to both more true
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and false identifications of tail damage. Thus, if the goal is to identify tail damage as soon as possible, then the lowered tail posture may be an even more sensitive detector of both immediate and future tail damage.
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However, for the farmer, the tucked tail may be easier to observe with certainty.
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4.1 Changes in tail posture prior to bleeding tail damage The results of the current study suggest that pen level tail posture could be a promising early detector of tail
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biting in finishing pigs, but only in pens with undocked pigs. However, it is still unknown when the higher probability of having a lowered tail arises in the case pens, as no increase in this behaviour was seen during the last 3 days prior to bleeding tail damage. This contradicts to the results found by Lahrmann et al. (2018) who, besides seeing more lowered tails in case pens compared to control pens, also found an increase in number of lowered tails from the second last to the last day prior to tail damage. Lahrmann et al. (2018) 12
used the same method as in the current study, except that they studied undocked weaners and that they used a more severe definition of day0 with more pigs affected (at least four pigs with tail wounds, and on average nine, independent of the freshness of the wound). Most likely as a consequence of this more severe definition of day0, they also saw generally a higher proportion of lowered tails these last 3 days. Further,
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the definition used may explain the difference in the results, as case pens in the study by Lahrmann et al. (2018) had the potential to increase the number of pigs with tail damage prior to day0. In the current study, some pens were also scored with non-bleeding tail wounds prior to day0, but the number of pens affected was similar between case and control pens. Also, this was accounted for in the statistical model and seemed to affect the tail posture of pigs to the same degree as being scored as a case pen. Zonderland et al. (2009)
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also observed that not just tail wounds but also bite marks were related to lowered tails in undocked weaner
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pigs. Thus, the tail posture of pigs seems to be affected both by ongoing tail biting and by the number of
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pigs affected. This suggests that to observe a change in tail posture prior to tail damage, a less severe
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definition of day0 should be used than the one used in the current study. The effect of ongoing tail biting may also explain why the same results were not obtained when observing tail posture directly in the stable.
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Here, the majority of the case and control pens showed signs of ongoing tail biting in the form of non-
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bleeding tail wounds, and thus the effect of being scored as a case pen may be less clear. However, it could also be due to the observation method used, which may have disturbed the pigs to such a degree that it
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dimished the effect of tail biting and tail damage on tail posture. During the observations, the curious pigs surrounded the observer and ended up standing behind each other. This may have resulted in some pigs
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protecting their tail, irrespective of whether they had previously been tail bitten or had damage on their tail. This may also explain why a higher probability of having a lowered tail was seen in pens with the high
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stocking density (also representing a larger group size), as more pigs would be in this situation. Why this was not seen for the observation days prior to day0 may be due to the fact that most recordings of case pens occurred during the first half of the study period where the pigs may not take up enough space to show this effect of high stocking density. Thus, when observing tail posture in relation to tail biting or tail damage, it is important to minimise the level of disturbance that occurs during the observations. In the current study, 13
this was accomplished by observing from video recordings. The video recordings were only performed on pens with undocked pigs, and thus it is unknown whether the same results would have been found in the pens with docked pigs.
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4.2 The effect of risk factors to tail damage on the tail posture of pigs
Statham et al. (2009) found a higher number of tucked tails prior to day0 longer back than 1 week. This could be explained by ongoing tail biting or it could argue that the tail posture of pigs is affected by other factors than merely tail biting and tail damage. In the current study, lack of straw provison, high stocking density and raising pigs with undocked tails seemed to affect the tail posture of pigs with an increase in the
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probability of having a lowered tail. A possible explanation for the effect of stocking density was presented
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in section 4.1. Lack of straw provision affected the tail posture both generally for the entire study period
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and on the observation days prior to day0, but only when observed from video recordings. Pigs are
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considered to have a behavioural need to explore their environment (Studnitz et al., 2007). The EU legislation states that pigs must have access to a sufficient quantity of material to enable proper investigation
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and manipulation activities (EU Council Directive 2008/120/EC) where straw provided on the floor has
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been suggested as one of the materials that can stand alone, as it is manipulable, investigable, chewable and edible (EU Commission 2016). Lack of proper enrichment such as straw may work as a stressor that may
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be affecting the tail posture of pigs directly. Advocating for this first suggestion is the fact that an effect of lack of straw was found when also accounting for ongoing tail biting and tail damage. However, lack of
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straw provision is also a risk factor of tail damage (Larsen et al., 2017). Pigs not provided with straw in the current study may increase their interest in pen mates’ tails due to their unfilled need to explore their
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environment (Van Putten, 1980; Petersen et al., 1995), thus leading to a lowered tail. The results also advocate for this second suggestion, as the effect of lack of straw could not be confirmed for the observations made directly in the stable prior to day0 and, as discussed in section 4.1, the direct observation method was suggested to diminish the effect of ongoing tail biting. Having an undocked tail also increased the probability of having a lowered tail both prior to day0 and for the full study period, independent of 14
whether tail damage occured or not. Also, most pens with tail-docked pigs were scored with non-bleeding tail wounds prior to day0, and thus this effect of being undocked was probably not related to ongoing tail biting. Instead, it suggests that the undocked tail could be easier to lower and tuck between the legs than the docked tail. Again, this confirms that changes in tail posture seem most suitable as an early detector of
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tail biting in pens with undocked pigs.
5. Conclusions
Having a tucked tail increased the odds of the same pig being scored with a tail wound on the same day. Thus, a tucked tail can be used as a detector of tail damage at pig level but will also lead to many false
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identifications. Tail posture observed at pen level and in an undisturbed way in finishing pigs seemed like
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a promising early detector of tail biting, although only in pens with undocked pigs. Future research could
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focus on the tail posture longer back than 3 days from bleeding tail damage, or alternatively using a less
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severe tail damage definition of a case pen to observe when the change in tail posture arises. Further, the differences in probability of having a lowered tail were relatively small, which suggests that future research
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could also focus on developing an automatic method for observing a lowered tail at pen level. In addition,
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the tail posture of pigs was also affected by risk factors of tail damage including lack of straw provision
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and a high stocking density, but the exact reason why is still unknown.
6. Conflict of interest statement
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None of the authors of this paper has a financial or personal relationship with other people or organisations
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who could inappropriately influence or bias the content of this paper.
7. Acknowledgement This work was supported by the Green Development and Demonstration Programme under the Ministry of Food, Agriculture and Fisheries, Denmark (project IntactTails j.nr. 34009-13-0743). The authors thank all the technicians and student helpers doing the experimental work and video observations: Betty Skou, 15
Carsten Kjærulff Christensen, Birthe Houbak, John Misa Obidah, Anna Gustafsson, Johanne Jespersen,
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Maja Bertelsen and Louise Bendixen. Also thanks to the stable personnel for a high level of cooperation.
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References Bates, D., Maechler, M., Bolker, B., Walker, W., 2015. Fitting Linear Mixed-Effects Models Using lme4. Journal of Statistical Software 67, 1-48. BEK nr. 1324. Provision on tail docking and castration of animals (Bekendtgørelse om halekupering og kastration ad dyr), 29/11/2017.
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Di Giminiani, P., Edwards, S.A., Malcolm, E.M., Leach, M.C., Herskin, M.S., Sandercock, D.A., 2017. Characterization of short-and long-term mechanical sensitisation following surgical tail amputation in pigs. Scientific Reports 7. EU Commission 2016. Staff Working Document on best practices with a view to the prevention of routine tail-docking and the provision of enrichment materials to pigs. 8/3/2016. EU Council Directive 2008/120/EC. Laying down minimum standards for the protection of pigs. 18/12/2008.
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Herskin, M.S., Di Giminiani, P., Thodberg, K., 2016. Effects of administration of a local anaesthetic and/or an NSAID and of docking length on the behaviour of piglets during 5 h after tail docking. Research in Veterinary Science 108, 60-67.
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Herskin, M.S., Thodberg, K., Jensen, H.E., 2015. Effects of tail docking and docking length on neuroanatomical changes in healed tail tips of pigs. Animal 9, 677-681.
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Lahrmann, H.P., Busch, M., D’Eath, R., Forkman, B., Hansen, C., 2017. More tail lesions among undocked than tail docked pigs in a conventional herd. animal, 1-7.
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Lahrmann HP, Hansen CF, D’Eath R, Busch ME and Forkman B 2018. Tail posture predicts tail biting outbreaks at pen level in weaner pigs. Applied Animal Behaviour Science 200, 29-35. Larsen, M.L.V., Andersen, H.M.-L., Pedersen, L.J., 2016. Can tail damage outbreaks in the pig be predicted by behavioural change? The Veterinary Journal 209, 50-56.
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Larsen, M.L.V., Andersen, H.M.-L., Pedersen, L.J., 2017. Which is the most preventive measure against tail damage in finisher pigs: tail docking, straw provision or lowered stocking density? animal, doi:10.1017/S175173111700249X. Munsterhjelm, C., Brunberg, E., Heinonen, M., Keeling, L., Valros, A., 2013. Stress measures in tail biters and bitten pigs in a matched case-control study. Animal Welfare 22, 331-338.
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Noonan, G.J., Rand, J.S., Priest, J., Ainscow, J., Blackshaw, J.K., 1994. Behavioral observations of piglets undergoing tail docking, teeth clipping and ear notching. Applied Animal Behaviour Science 39, 203-213.
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Petersen, V., Simonsen, H.B., Lawson, L.G., 1995. The effect of environmental stimulation on the development of behaviour in pigs. Applied Animal Behaviour Science 45, 215-224. R Core Team, 2017. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL: https://www.R-project.org/. Simonsen, H.B., Klinken, L., Bindseil, E., 1991. Histopathology of intact and docked pigtails. British Veterinary Journal 147, 407-412. Statham, P., Green, L., Bichard, M., Mendl, M., 2009. Predicting tail-biting from behaviour of pigs prior to outbreaks. Applied Animal Behaviour Science 121, 157-164. 17
Studnitz, M., Jensen, M.B., Pedersen, L.J., 2007. Why do pigs root and in what will they root? A review on the exploratory behaviour of pigs in relation to environmental enrichment. Applied Animal Behaviour Science 107, 183-197. Sutherland, M.A., Bryer, P.J., Krebs, N., McGlone, J.J., 2009. The effect of method of tail docking on tailbiting behaviour and welfare of pigs. Animal Welfare 18, 561-570.
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Taylor, N.R., Main, D.C., Mendl, M., Edwards, S.A., 2010. Tail-biting: a new perspective. The Veterinary Journal 186, 137-147. Valros, A., Munsterhjelm, C., Puolanne, E., Ruusunen, M., Heinonen, M., Peltoniemi, O.A.T., Poso, A.R., 2013. Physiological indicators of stress and meat and carcass characteristics in tail bitten slaughter pigs. Acta Veterinaria Scandinavica 55. Van Putten, G., 1980. Objective observations on the behaviour of fattening pigs. Animal Regulation Studies 3, 105-188.
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Wallgren, T., Westin, R., Gunnarsson, S., 2016. A survey of straw use and tail biting in Swedish pig farms rearing undocked pigs. Acta Veterinaria Scandinavica 58, 84.
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Zonderland, J.J., van Riel, J.W., Bracke, M.B., Kemp, B., den Hartog, L.A., Spoolder, H.A., 2009. Tail posture predicts tail damage among weaned piglets. Applied Animal Behaviour Science 121, 165-170.
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Figure legends Figure 1. Pen designs used in the study: (A) pen for finishing pigs with 1.21 m2/pig (11 pigs/pen), (B) pen for finishing pigs with 0.73 m2/pig (18 pigs/pen). Feeders with either two or three feeding places are
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represented by the white rectangles, drinking cups by the black hollow circles, and the two solid black squares represent two hard wooden sticks in separate vertical racks provided as general enrichment for all pens.
Figure 2. The probability of having a lowered tail among the standing pigs in the pen. Pens were either
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control pens (C) or case pens (TD), were either not scored with at least one non-bleeding tail wound the
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last 3 observation days prior to day0 (TW no) or were (TW yes), and were either provided with straw (S)
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or not provided with straw (NS). Difference in lower case letters (a, b) shows a significant difference
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between levels of either factor.
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Figure 3. The probability of having a lowered tail in the pen. Pens either had docked or undocked pigs and were either observed on days with tail biting (two observations prior to and after the recording of a bleeding
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tail wound in the specific pen) or on days without tail biting (all other observation days during the study period). Difference in lower case letters (a, b) shows a significant difference between pens with docked and
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undocked pigs. Difference in upper case letters (A, B) shows a significant difference between observation
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days with and without tail biting.
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20
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Table 1. Number of observations (on individual pig level) scored with a tail wound (both non-bleeding and bleeding tail wounds included) and a bleeding tail wound combined with an observation of the tail tucked between the legs.
Tail wound (n)
Bleeding tail wound (n)
No
Yes
% Yes
21499
20460
1039
4.8
No
21369
20367
1002
4.7
Yes
130
93
37
28.5
Total (n)
No
Yes
% Yes
21442
57
0.3
21323
46
0.2
119
11
8.5
A
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A
N
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Tail between legs (n)
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Total (n)
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S0168-1591(18)30465-9 https://doi.org/10.1016/j.applanim.2018.08.016 APPLAN 4702
To appear in:
APPLAN
Received date: Revised date: Accepted date:
30-1-2018 6-6-2018 21-8-2018
Please cite this article as: Vestbjerg Larsen ML, Andersen HM-Lis, Pedersen LJ, Tail posture as a detector of tail damage and an early detector of tail biting in finishing pigs, Applied Animal Behaviour Science (2018), https://doi.org/10.1016/j.applanim.2018.08.016 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Tail posture as a detector of tail damage and an early detector of tail biting in finishing pigs
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Mona Lilian Vestbjerg Larsena*, Heidi Mai-Lis Andersenb, Lene Juul Pedersena
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Department of Animal Science, Aarhus University, Blichers Allé 20, 8830 Tjele, Denmark
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* Corresponding author. Tel.: +45 5150 7927.
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E-mail address: [email protected] (M. L. V. Larsen)
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Department of Agroecology, Aarhus University, Blichers Allé 20, 8830 Tjele, Denmark
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A tucked tail worked as a detector of tail damage in finishers Tail posture seemed promising as an early detector of tail biting in finishers Tail posture was affected by risk factors of tail damage
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Highlights
Abstract
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The purpose of the current study was to investigate the relation between the tail posture of finishing pigs and tail damage with the aims to use tail posture as (1) an detector of tail damage, (2) an early detector of
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tail biting to possibly predict and prevent bleeding tail damage. Tails of each individual pig (from 112 finishing pigpens) were scored three times per week for the full study period of 10 weeks. For the first aim,
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tail posture was observed directly in the stable three times per week, just prior to tail scoring, and pigs with a tucked tail were related to their tail scoring. The odds of being scored with a tail wound (both bleeding and non-bleeding) increased by almost sixfold if the pig was also observed with a tucked tail on the same day. More precisely, 28% of the pigs with a tucked tail were also scored with a tail wound, whereas this was only the case for 5% of the pigs with a different tail posture. This relation between a tucked tail and 1
tail damage was larger than previously found in weaners and suggests that a tucked tail could be used as an detector of tail damage, although with the risk of many false identifications of tail damage. For the second aim, tail posture was observed from video the last 3 days prior to bleeding tail damage for case pens (n=20; at least one pig with a bleeding tail wound) and their matched controls (n=20). The number of pigs with
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lowered tails (below the tail root) was observed by scan sampling during 6 h per day. A generally higher probability of having a lowered tail was seen in the case pens compared to the control pens, but the probability of having a lowered tail did not increase prior to bleeding tail damage. Thus, the results indicate that tail posture is a promising early detector of tail biting in finishing pigs, but observations going further back than 3 days from bleeding tail damage are needed to find out when the difference in tail posture arises.
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Alternatively, a less severe definition of tail damage could be used. Further, the differences found were
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relatively small, and thus to be able to predict pens in future risk of tail damage from changes in tail posture
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would probably demand the development of an automatic recording method for the number of lowered tails
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at pen level.
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Keywords: Finishing pigs; Tail posture; Tail damage; Early detection; Straw provision; Stocking density
1. Introduction
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Many pigs raised according to conventional production standards are tail docked due to its preventive effect against tail damage developed from tail biting. Tail biting is an animal welfare problem due to its negative
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consequences, such as experienced stress and pain in the pig (e.g. Munsterhjelm et al., 2013; Valros et al., 2013; Di Giminiani et al., 2017) and the fact that the biter probably performs the tail biting behaviour due to an internal frustration arising from lack of important resources such as lack of proper enrichment to fulfil the exploratory need of the pig (Taylor et al., 2010). However, pigs being tail docked also experience stress and pain during the procedure (Noonan et al., 1994; Herskin et al., 2016) and perhaps in the long term 2
(Simonsen et al., 1991; Herskin et al., 2015). Further, tail docking does not eliminate the occurrence of tail biting or tail damage (e.g. Sutherland et al., 2009; Larsen et al., 2017). Thus, as stated by the EU legislation (EU Council Directive 2008/120/EC), tail docking is only allowed to be performed if injuries to the pigs’ tail occur at the herd and if other preventive measures have been tried first such as improving the
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environment of the pigs. However, allocation of preventive measures may not always be enough to prevent tail damage, especially in undocked pigs (Larsen et al., 2017). Thus, an alternative strategy that could be used simultaneously with the allocation of preventive measures is early detection of tail biting to identify pens in risk of future tail damage. If the farmer was alarmed about pens in high risk of tail damage, then the farmer would be able to make temporary interventions against tail biting that it may not be possible to
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perform for the entire production period. The first step in developing and implementing such a strategy is
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to identify early detectors of tail biting, which for example could be behavioural changes observed prior to
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tail damage. As mentioned, both tail docking and tail biting are painful experiences for the pig. Noonan et
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al. (1994) found that tail-docked pigs tucked their tails between the legs just after the procedure, and they did it more than sham-handled pigs and pigs experiencing other mutilations, such as ear notching or teeth
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clipping. Thus, the experience of tail biting may also cause the pig to lower its tail for example to protect
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the tail from further biting. Larsen et al. (2016) summarised the literature on behavioural changes seen prior to tail damage and identified changes in the tail posture of pigs to be a possible early detector of tail biting
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that deserves more investigation. Only one study has investigated tail posture and its relation to tail biting and tail damage in finishing pigs (from 30 kg until slaughter), and this did not include observations of tail
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posture close in time to the occurrence of tail damage (Statham et al., 2009). This has been investigated in weaners (Zonderland et al., 2009; Lahrmann et al., 2018) and deserves investigation in finishing pigs, as
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the majority of tail damages, definitely in undocked pigs, occur in this phase of the production (Wallgren et al., 2016; Lahrmann et al., 2017). Zonderland et al. (2009) also found a relation between tail posture and tail damage when observed on the same day, which has not been investigated in finishing pigs either. Further, it is unknown whether tail posture and tail damage are directly related due to for example the need to protect the tail or it being the most comfortable posture when injured, or whether they are indirectly 3
related through the relation between tail posture and other stressors leading to tail damage such as lack of enrichment or high stocking density. The current study had three aims: (1) to investigate whether a relation existed for the individual finishing
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pig between tail posture and tail damage when observed on the same day, (2) to investigate whether pen level tail posture in finishing pigs changed prior to bleeding tail damage and whether it differed between pens scored with and not scored with bleeding tail damage and (3) to investigate whether risk factors of tail damage affected pen level tail posture. It was hypothesised that pigs with a tail tucked between the legs would have a higher risk of being simultaneously scored with tail damage, that the number of lowered tails
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would increase prior to bleeding tail damage, and that the number of lowered tails would be higher in the
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pens scored with bleeding tail damage compared to the pens not scored with bleeding tail damage.
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2. Materials and methods
Further information about the study not included here can be found in Larsen et al. (2017). The study was
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no. 2015-15-0201-00593).
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conducted in accordance with a protocol approved by the Danish Animal Experiments Inspectorate (Journal
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2.1 Animals, housing and management
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The experimental unit was 112 finishing pigpens divided between four batches (batch 1, 3, 4: 32 pens each; batch 2: 16 pens). A total of 1624 finishing pigs were included and inserted to the finishing pigunit at an
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average weight of 31.6 ± 6.6 kg at insertion. At insertion, all pigs were checked for damage on the tail, and no pigs with tail damage were included in the study. The finishing pigunit included two rooms (in batch 2, only one room was used), each with 16 identical finishing pigpens. The design and dimensions of the pens can be seen in Figure 1. To include stressors (undocked tails, no straw provided and high stocking density) that potentially would affect the tail posture of the pigs and which are considered risk factors of tail biting
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and tail damage, the pens within each batch were randomly divided between one level of each of three factors: (1) TAIL: pigs with undocked (n=52) or docked tails (n=60), (2) STRAW: not provided with straw (n=56) or provided with 150 g of straw per pig per day on the solid floor (n=56), (3) STOCK: stocking density of 0.73 m2/pig (n=56, 18 pigs per pen) or 1.21 m2/pig (n=56, 11 pigs per pen). Pigs were tail docked
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according to the Danish legislation to half of the tail’s original length with a hot-iron cutter within the first 4 days after birth (BEK nr. 1324). Further, the amount of feeding space per pig was kept approximately equal between the two stocking densities.
2.2 Tail damage – definition and identification
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A pen was recorded as a case pen when at least one pig in the pen was observed with a bleeding tail wound.
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In the following, this day is reffered to as day0 for the respective case pen. After the scoring of the first
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bleeding tail wound in the pen, the pen was no longer included in the study, and pigs with bleeding tail
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wounds were moved to sick pens. Pen level tail scorings were performed daily by the stock personnel from outside the pen, while more detailed tail scorings were conducted each Monday, Wednesday and Friday in
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each of the 10 weeks of the study period after the observation of tail posture (described in section 2.3).
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These detailed tail scorings were performed each scoring day by two observers by entering the pen and scoring each individual tail according to its length, damage and blood freshness if present. Batch 1 included
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five different observers who were all trained according to a scoring protocol with pictures and text, both by group discussions and practical scorings in the stable. Batch 2 included four observers, all of whom were
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also included in batch 1. Batch 3 included five observers of whom one was new and trained by the others. Batch 4 included four observers, of whom one was new and trained by the others. Blinding of observers
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was not possible due to the obviousness of the factors TAIL, STRAW and STOCK.
2.3 Behavioural observations Tail posture was observed both directly in the stable and from video recordings. The direct observations were conducted only in batch 1, 2 and 3 each Monday, Wednesday and Friday in the morning between 0800 5
and 1000 h. This was not conducted in batch 4 due to workload limitations. Thus, these observations were performed on 80 finishing pigpens and for the full study period of 10 weeks per batch. During the observations, the observer entered the pen, woke up the pigs and made sure that all pigs were standing. Afterwards, the observer was standing still in the pen counting the number of pigs with a hangning tail
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posture (the tail is either in a straigt line from the tail root or below the horizontal line from the tail root), number of pigs with the tail tucked between the legs and the total number of pigs in the pen. The identification number of pigs with a tucked tail posture was also recorded. When referring to a lowered tail in the following sections, this is the sum of the number of pigs with the hanging and tucked tail postures. No one, despite the observers, entered the pen or the rooms of the finishing pigunit on that particular day
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before tail posture had been observed. These observations were performed by the same trained observers
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as for tail scoring. Blinding of the observers was not possible due to the obviousness of the factors TAIL,
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STRAW and STOCK. However, tails were scored after the observation of tail posture, and thus the
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observers did not know whether tail damage was present in each pen. Tail posture was observed from video recordings during batch 1, 3 and 4, but only in pens with undocked
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pigs. Batch 2 could not be included, as no matched control pens were available (batch 2 only included four
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pens with undocked pigs due to delivery problems of undocked pigs during this batch). To obtain the video recordings, a camera (Monacor, TYPE-TVCCD-170S, Bremen, Germany) was installed about 3 m above
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the solid floor in each pen, ensuring a full view of the entire pen. These observations were performed the last 3 days prior to day0 (to replicate the method used by Lahrmann et al. (2018)) from 0800-1100 h
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(morning) and from 1530-1830 h (afternoon) by scan sampling every 30 minutes. At each scan, the observer counted the number of standing pigs in the pen and the number of standing pigs with a lowered tail (the tail
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is below the horizontal line from the tail root, also including pigs with a tucked tail posture). The same observations were performed on the same days in one matched control pen per case pen. It was aimed to match case pens to control pens that were from the same batch, had the same combination of TAIL, STRAW and STOCK and that had never been scored with a bleeding tail wound throughout the 10 weeks of the study period. In five cases, the last criteria could not be fulfilled, and these case pens were instead paired 6
with control pens that had not been scored with bleeding tail damage prior to or 1 week after day0. This was accounted for in the statistical analysis and did not affect the results significantly (P>0.05). The video observations were performed by a single trained observer. This observer was not blinded to either the factors TAIL, STRAW and STOCK or whether the pen was a case or control pen. The pens were observed in a
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random order across batches.
2.4 Statistical Analysis
All statistical analyses were performed in R Version 3.2.4. (R Core Team, 2017) using the package ”lme4” (Bates et al., 2015) for generalised linear mixed models. Four models were created, all being logistic
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regression for binomial data using the function “glmer”. All models were reduced according to a 5-%
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significance level (P<0.05). Differences are presented as odds ratios with connected 95% confidence
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intervals (CI).
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2.4.1 A tucked tail as a detector of tail damage in individual pigs (Model 1)
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Model 1 used data on individual pig level from each observation day throughout the study period of 10 weeks or until the pen was recorded as a case pen. Thus, each pen, and thereby pig, had a different number
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of observation days depending on whether and when the pen was recorded as a case pen. A pig could have
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the tail tucked between the legs or not (TP), a bleeding tail wound or not (BTW) and a tail wound (both bleeding and non-bleeding) or not (TWpig), all three as binomial variables. Model 1 tested whether an
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observation of a tail tucked between the legs would increase the odds of finding a tail wound. For this purpose, a model was created including TWpig as a response variable, TP as a main effect and allowed for a random intercept for each pig identification number nested within pen number (1 to 32 within batch 1 and 3; 1 to 16 within batch 2) nested within batch number (1 to 3). It was not possible to make a similar model for the response BTW, as too few pigs were scored with a bleeding tail wound (see Table 1).
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2.4.2 Changes in tail posture prior to bleeding tail damage observed directly in the stable (Model 2) Each case pen was paired with one to three matched control pens depending on the availability within the
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batch. The matched control pens were from the same batch and had the same combination of the factors TAIL, STRAW and STOCK as their respective case pens but were not recorded as case pens throughout the 10-week study period. A pen could be a matched control pen to multiple case pens. A case pen and its matched control pens were observed on the exact same dates prior to the scoring of bleeding tail damage in the case pens (day0). Model 2 used tail posture data from the last 3 observation days prior to day0 (one
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week) obtained through direct observations in the stable. The model included data from 22 case pens and
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31 matched control pens combined in 22 pairs. Prior to analysis, a day category variable (DAY) with three
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levels relative to day0 was created: “day-1 to day-3”, “day-4 to day-5” and “day-6 to day-7”. This was done
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to ensure that all pens were represented in each category, as tail posture was not observed on all days during the week. Furthermore, to account for ongoing tail biting in both the case pens and control pens, a binomial
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non-bleeding tail wound variable (TWpen) was created. TWpen was assigned 1 if the pen had been scored
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with at least one non-bleeding tail wound during the last 3 observation days prior to day0 and 0 if the pen had not been scored with any non-bleeding tail wounds during these days. This was different from being
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scored as a case pen where at least one pig in the pen should have been scored with a bleeding tail wound. The response variable was the proportion of pigs with lowered tails out of the total number of pigs in the
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pen. The model included the main effects pen type (case v. control), DAY, TWpen, period number (1: week 1-3; 2: week 4-6; 3: week 7-10), STRAW, STOCK, TAIL and all two-way interactions between pen type
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and the other main effects DAY, TWpen, TAIL, STRAW and STOCK. Further, a random intercept was allowed for each pen number (1 to 32 within batch 1 and 3; 1 to 16 within batch 2) nested within pair number (1 to 22) nested within batch number (1 to 3). Estimated results from the model are presented as the probability of having a lowered tail in the pen (in percentages).
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2.4.3 Changes in tail posture prior to bleeding tail damage observed from video recordings (Model 3) Model 3 used data observed from video the last 3 days prior to day0. The model included data from 20 pairs
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of case and control pens, all with undocked pigs (thus, TAIL was not included in the model). Here, TW pen was assigned 1 if at least one pig in the pen had been scored with a non-bleeding tail wound during these 3 days and otherwise assigned 0. The response variable was the proportion of pigs with lowered tails out of the number of pigs standing in the pen. The model included the main effects pen type (case v. control), day (day-1 v. day-2 v. day-3), observation period (morning v. afternoon), TWpen, period number (1: week 1-3;
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2: week 4-6; 3: week 7-10), STRAW, STOCK and all two-way interactions between pen type and the main
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effects day, observation period, TWpen, STRAW and STOCK. Further, a random intercept was allowed for
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each pen number (1 to 32) nested within pair number (1 to 22) nested within batch number (1, 3 and 4).
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standing in the pen (in percentages).
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Estimated results from the model are presented as the probability of having a lowered tail among the pigs
2.4.4 Effect of straw provision, stocking density and tail docking on tail posture (Model 4)
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Model 4 used tail posture data observed directly in the stable for the full study period of 10 weeks. As tail damage was expected to affect the tail posture of pigs, this was accounted for by a binomial tail biting
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variable (TB). TB was assigned 1 for the 2 observation days prior to and after a recording of a bleeding tail wound for the specific pen, here termed ‘the days with tail biting’. It was assigned 0 on all other days, here
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termed ‘the days without tail biting’. For case pens, the detailed tail scoring ended after day0 for that specific pen, and afterwards, until the end of the study period, the TB variable was created based solely on the daily tail scorings performed by the stock people from outside the pen. The response variable was the proportion of pigs with lowered tails out of the total number of pigs in the pen. The model included the main effects TAIL, STRAW, STOCK, TB and period number (1: week 1-3; 2: week 4-6; 3: week 7-10) and all two-way 9
interactions between STRAW, STOCK, TAIL and TB. Further, a random intercept was allowed for each pen number (1 to 32 within batch 1 and 3; 1 to 16 within batch 2) nested within batch number (1 to 3).
3.1 A tucked tail as a detector of tail damage in individual pigs
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3. Results
Descriptive results can be seen in Table 1. If pigs were observed not having the tail tucked between the legs, 4.7% and 0.2% of those pigs were later that day scored with a tail wound (both non-bleeding and bleeding tail wounds included) and a bleeding tail wound, respectively. If pigs were observed having the
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tail tucked between the legs, 28.5% and 8.5% of those pigs were later that day observed with a tail wound
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and a bleeding tail wound, respectively. An effect was found of TP (P<0.001) showing that having the tail
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almost sixfold (OR = 5.87, 95% CI [3.92-9.08]).
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tucked between the legs increased the odds of finding a tail wound on the same pig on the same day by
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3.2 Changes in tail posture prior to bleeding tail damage When tail posture was observed directly in the stable (Model 2), only TAIL had a general effect (P<0.01)
CC
with a higher probability in pens with undocked pigs (6.99%) compared to pens with docked pigs (4.03%; OR = 1.79, 95% CI [1.25-2.58]), irrespective of whether the pen was a case or control pen. The probability
A
of having a lowered tail in the pen did not increase prior to bleeding tail damage, neither was it larger in the case pens compared to the control pens. Out of the 22 case pens and 31 control pens included, 19 and 23 of these were scored with at least one non-bleeding tail wound the last 3 observation days prior to day0, respectively, and the majority of these were pens with docked pigs (case pens = 15; control pens = 16).
10
When tail posture was observed from video recordings the last 3 days prior to day0 for pens with undocked pigs (Model 3), an effect was found of pen type (P<0.05; OR = 1.60, 95% CI [1.14-2.23]), TWpen (P<0.05; OR = 1.65, 95% CI [1.25-2.52]) and STRAW (P<0.001; OR = 2.41, 95% CI [1.57-3.71]). All three results are illustrated in Figure 2. The probability of having a lowered tail among the pigs standing in the pen did
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not increase prior to bleeding tail damage. Out of the 20 case pens and 20 control pens included, seven and six of these were scored with at least one non-bleeding tail wound the last 3 observation days prior to day0, respectively.
3.3 Effect of straw provision, stocking density and tail docking on tail posture
U
For the full study period when tail posture was observed directly in the stable (Model 4), an effect was
N
found of STRAW (P<0.001) and STOCK (P<0.001). A higher probability of having a lowered tail was
A
seen in pens without straw (3.74%) compared to pens with straw (2.70%; OR = 1.40, 95% CI [1.17-1.67])
M
and in pens with high stocking density (5.35%) compared to low stocking density (3.74%; OR = 1.46, 95% CI [1.22-1.74]). Further, a two-way interaction was found between TAIL and TB (P<0.05) with a higher
D
probability of having a lowered tail in pens with undocked pigs, both on days with (OR = 2.84, 95% CI
TE
[2.10-3.82]) and without tail biting (OR = 2.03, 95% CI [1.68-2.44]) and with a higher probability of having a lowered tail on the days with tail biting in pens with undocked pigs (OR = 1.27, 95% CI [1.09-1.49]). The
CC
EP
result is illustrated in Figure 3.
Discussion
A
The odds of being scored with a tail wound (non-bleeding and bleeding) increased when the pig was scored with a tucked tail on the same day. Further, case pens with undocked pigs observed from video recordings showed a higher probability of having a lowered tail compared to the control pens on all 3 days prior to day0. However, the probability of having a lowered tail did not increase prior to bleeding tail damage. The
11
probability of having a lowered tail was higher in pens with no straw provision, in pens with the high stocking density and in pens with undocked pigs.
4.1 A tucked tail as an immediate detector of tail damage
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A relation was found between having a tucked tail and tail damage with increased odds of scoring a pig with a tail wound if the same pig was also scored with a tucked tail on the same day. Similar results were found by Zonderland et al. (2009) who studied undocked weaners. They saw that for pigs with a lowered tail, 30% had bite marks or tail wounds (with dried or fresh blood) on the tail, and this was 9% for pigs with a tail tucked between the legs. The current study found an even greater relation between a tucked tail and
U
tail damage in finishing pigs with 28% of the pigs with a tucked tail also being scored with a tail wound
N
(either bleeding or non-bleeding). However, results from both the current study and the study by Zonderland
A
et al. (2009) also clearly demonstrated that using a tucked tail as a detector of tail damage will lead to many
M
false identifications and false rejections of tail damage. The current study mostly focused on the lowered tail posture, as only few tucked tails were observed. However, Zonderland et al. (2009) showed that the
D
lowered tail compared to the tucked tail as an immediate detector of tail damage will lead to both more true
TE
and false identifications of tail damage. Thus, if the goal is to identify tail damage as soon as possible, then the lowered tail posture may be an even more sensitive detector of both immediate and future tail damage.
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However, for the farmer, the tucked tail may be easier to observe with certainty.
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4.1 Changes in tail posture prior to bleeding tail damage The results of the current study suggest that pen level tail posture could be a promising early detector of tail
A
biting in finishing pigs, but only in pens with undocked pigs. However, it is still unknown when the higher probability of having a lowered tail arises in the case pens, as no increase in this behaviour was seen during the last 3 days prior to bleeding tail damage. This contradicts to the results found by Lahrmann et al. (2018) who, besides seeing more lowered tails in case pens compared to control pens, also found an increase in number of lowered tails from the second last to the last day prior to tail damage. Lahrmann et al. (2018) 12
used the same method as in the current study, except that they studied undocked weaners and that they used a more severe definition of day0 with more pigs affected (at least four pigs with tail wounds, and on average nine, independent of the freshness of the wound). Most likely as a consequence of this more severe definition of day0, they also saw generally a higher proportion of lowered tails these last 3 days. Further,
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the definition used may explain the difference in the results, as case pens in the study by Lahrmann et al. (2018) had the potential to increase the number of pigs with tail damage prior to day0. In the current study, some pens were also scored with non-bleeding tail wounds prior to day0, but the number of pens affected was similar between case and control pens. Also, this was accounted for in the statistical model and seemed to affect the tail posture of pigs to the same degree as being scored as a case pen. Zonderland et al. (2009)
U
also observed that not just tail wounds but also bite marks were related to lowered tails in undocked weaner
N
pigs. Thus, the tail posture of pigs seems to be affected both by ongoing tail biting and by the number of
A
pigs affected. This suggests that to observe a change in tail posture prior to tail damage, a less severe
M
definition of day0 should be used than the one used in the current study. The effect of ongoing tail biting may also explain why the same results were not obtained when observing tail posture directly in the stable.
D
Here, the majority of the case and control pens showed signs of ongoing tail biting in the form of non-
TE
bleeding tail wounds, and thus the effect of being scored as a case pen may be less clear. However, it could also be due to the observation method used, which may have disturbed the pigs to such a degree that it
EP
dimished the effect of tail biting and tail damage on tail posture. During the observations, the curious pigs surrounded the observer and ended up standing behind each other. This may have resulted in some pigs
CC
protecting their tail, irrespective of whether they had previously been tail bitten or had damage on their tail. This may also explain why a higher probability of having a lowered tail was seen in pens with the high
A
stocking density (also representing a larger group size), as more pigs would be in this situation. Why this was not seen for the observation days prior to day0 may be due to the fact that most recordings of case pens occurred during the first half of the study period where the pigs may not take up enough space to show this effect of high stocking density. Thus, when observing tail posture in relation to tail biting or tail damage, it is important to minimise the level of disturbance that occurs during the observations. In the current study, 13
this was accomplished by observing from video recordings. The video recordings were only performed on pens with undocked pigs, and thus it is unknown whether the same results would have been found in the pens with docked pigs.
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4.2 The effect of risk factors to tail damage on the tail posture of pigs
Statham et al. (2009) found a higher number of tucked tails prior to day0 longer back than 1 week. This could be explained by ongoing tail biting or it could argue that the tail posture of pigs is affected by other factors than merely tail biting and tail damage. In the current study, lack of straw provison, high stocking density and raising pigs with undocked tails seemed to affect the tail posture of pigs with an increase in the
U
probability of having a lowered tail. A possible explanation for the effect of stocking density was presented
N
in section 4.1. Lack of straw provision affected the tail posture both generally for the entire study period
A
and on the observation days prior to day0, but only when observed from video recordings. Pigs are
M
considered to have a behavioural need to explore their environment (Studnitz et al., 2007). The EU legislation states that pigs must have access to a sufficient quantity of material to enable proper investigation
D
and manipulation activities (EU Council Directive 2008/120/EC) where straw provided on the floor has
TE
been suggested as one of the materials that can stand alone, as it is manipulable, investigable, chewable and edible (EU Commission 2016). Lack of proper enrichment such as straw may work as a stressor that may
EP
be affecting the tail posture of pigs directly. Advocating for this first suggestion is the fact that an effect of lack of straw was found when also accounting for ongoing tail biting and tail damage. However, lack of
CC
straw provision is also a risk factor of tail damage (Larsen et al., 2017). Pigs not provided with straw in the current study may increase their interest in pen mates’ tails due to their unfilled need to explore their
A
environment (Van Putten, 1980; Petersen et al., 1995), thus leading to a lowered tail. The results also advocate for this second suggestion, as the effect of lack of straw could not be confirmed for the observations made directly in the stable prior to day0 and, as discussed in section 4.1, the direct observation method was suggested to diminish the effect of ongoing tail biting. Having an undocked tail also increased the probability of having a lowered tail both prior to day0 and for the full study period, independent of 14
whether tail damage occured or not. Also, most pens with tail-docked pigs were scored with non-bleeding tail wounds prior to day0, and thus this effect of being undocked was probably not related to ongoing tail biting. Instead, it suggests that the undocked tail could be easier to lower and tuck between the legs than the docked tail. Again, this confirms that changes in tail posture seem most suitable as an early detector of
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tail biting in pens with undocked pigs.
5. Conclusions
Having a tucked tail increased the odds of the same pig being scored with a tail wound on the same day. Thus, a tucked tail can be used as a detector of tail damage at pig level but will also lead to many false
U
identifications. Tail posture observed at pen level and in an undisturbed way in finishing pigs seemed like
N
a promising early detector of tail biting, although only in pens with undocked pigs. Future research could
A
focus on the tail posture longer back than 3 days from bleeding tail damage, or alternatively using a less
M
severe tail damage definition of a case pen to observe when the change in tail posture arises. Further, the differences in probability of having a lowered tail were relatively small, which suggests that future research
D
could also focus on developing an automatic method for observing a lowered tail at pen level. In addition,
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the tail posture of pigs was also affected by risk factors of tail damage including lack of straw provision
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and a high stocking density, but the exact reason why is still unknown.
6. Conflict of interest statement
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None of the authors of this paper has a financial or personal relationship with other people or organisations
A
who could inappropriately influence or bias the content of this paper.
7. Acknowledgement This work was supported by the Green Development and Demonstration Programme under the Ministry of Food, Agriculture and Fisheries, Denmark (project IntactTails j.nr. 34009-13-0743). The authors thank all the technicians and student helpers doing the experimental work and video observations: Betty Skou, 15
Carsten Kjærulff Christensen, Birthe Houbak, John Misa Obidah, Anna Gustafsson, Johanne Jespersen,
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A
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Maja Bertelsen and Louise Bendixen. Also thanks to the stable personnel for a high level of cooperation.
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References Bates, D., Maechler, M., Bolker, B., Walker, W., 2015. Fitting Linear Mixed-Effects Models Using lme4. Journal of Statistical Software 67, 1-48. BEK nr. 1324. Provision on tail docking and castration of animals (Bekendtgørelse om halekupering og kastration ad dyr), 29/11/2017.
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Di Giminiani, P., Edwards, S.A., Malcolm, E.M., Leach, M.C., Herskin, M.S., Sandercock, D.A., 2017. Characterization of short-and long-term mechanical sensitisation following surgical tail amputation in pigs. Scientific Reports 7. EU Commission 2016. Staff Working Document on best practices with a view to the prevention of routine tail-docking and the provision of enrichment materials to pigs. 8/3/2016. EU Council Directive 2008/120/EC. Laying down minimum standards for the protection of pigs. 18/12/2008.
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Herskin, M.S., Di Giminiani, P., Thodberg, K., 2016. Effects of administration of a local anaesthetic and/or an NSAID and of docking length on the behaviour of piglets during 5 h after tail docking. Research in Veterinary Science 108, 60-67.
A
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Herskin, M.S., Thodberg, K., Jensen, H.E., 2015. Effects of tail docking and docking length on neuroanatomical changes in healed tail tips of pigs. Animal 9, 677-681.
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Lahrmann, H.P., Busch, M., D’Eath, R., Forkman, B., Hansen, C., 2017. More tail lesions among undocked than tail docked pigs in a conventional herd. animal, 1-7.
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Lahrmann HP, Hansen CF, D’Eath R, Busch ME and Forkman B 2018. Tail posture predicts tail biting outbreaks at pen level in weaner pigs. Applied Animal Behaviour Science 200, 29-35. Larsen, M.L.V., Andersen, H.M.-L., Pedersen, L.J., 2016. Can tail damage outbreaks in the pig be predicted by behavioural change? The Veterinary Journal 209, 50-56.
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Larsen, M.L.V., Andersen, H.M.-L., Pedersen, L.J., 2017. Which is the most preventive measure against tail damage in finisher pigs: tail docking, straw provision or lowered stocking density? animal, doi:10.1017/S175173111700249X. Munsterhjelm, C., Brunberg, E., Heinonen, M., Keeling, L., Valros, A., 2013. Stress measures in tail biters and bitten pigs in a matched case-control study. Animal Welfare 22, 331-338.
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Noonan, G.J., Rand, J.S., Priest, J., Ainscow, J., Blackshaw, J.K., 1994. Behavioral observations of piglets undergoing tail docking, teeth clipping and ear notching. Applied Animal Behaviour Science 39, 203-213.
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Petersen, V., Simonsen, H.B., Lawson, L.G., 1995. The effect of environmental stimulation on the development of behaviour in pigs. Applied Animal Behaviour Science 45, 215-224. R Core Team, 2017. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL: https://www.R-project.org/. Simonsen, H.B., Klinken, L., Bindseil, E., 1991. Histopathology of intact and docked pigtails. British Veterinary Journal 147, 407-412. Statham, P., Green, L., Bichard, M., Mendl, M., 2009. Predicting tail-biting from behaviour of pigs prior to outbreaks. Applied Animal Behaviour Science 121, 157-164. 17
Studnitz, M., Jensen, M.B., Pedersen, L.J., 2007. Why do pigs root and in what will they root? A review on the exploratory behaviour of pigs in relation to environmental enrichment. Applied Animal Behaviour Science 107, 183-197. Sutherland, M.A., Bryer, P.J., Krebs, N., McGlone, J.J., 2009. The effect of method of tail docking on tailbiting behaviour and welfare of pigs. Animal Welfare 18, 561-570.
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Taylor, N.R., Main, D.C., Mendl, M., Edwards, S.A., 2010. Tail-biting: a new perspective. The Veterinary Journal 186, 137-147. Valros, A., Munsterhjelm, C., Puolanne, E., Ruusunen, M., Heinonen, M., Peltoniemi, O.A.T., Poso, A.R., 2013. Physiological indicators of stress and meat and carcass characteristics in tail bitten slaughter pigs. Acta Veterinaria Scandinavica 55. Van Putten, G., 1980. Objective observations on the behaviour of fattening pigs. Animal Regulation Studies 3, 105-188.
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Wallgren, T., Westin, R., Gunnarsson, S., 2016. A survey of straw use and tail biting in Swedish pig farms rearing undocked pigs. Acta Veterinaria Scandinavica 58, 84.
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Zonderland, J.J., van Riel, J.W., Bracke, M.B., Kemp, B., den Hartog, L.A., Spoolder, H.A., 2009. Tail posture predicts tail damage among weaned piglets. Applied Animal Behaviour Science 121, 165-170.
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Figure legends Figure 1. Pen designs used in the study: (A) pen for finishing pigs with 1.21 m2/pig (11 pigs/pen), (B) pen for finishing pigs with 0.73 m2/pig (18 pigs/pen). Feeders with either two or three feeding places are
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represented by the white rectangles, drinking cups by the black hollow circles, and the two solid black squares represent two hard wooden sticks in separate vertical racks provided as general enrichment for all pens.
Figure 2. The probability of having a lowered tail among the standing pigs in the pen. Pens were either
U
control pens (C) or case pens (TD), were either not scored with at least one non-bleeding tail wound the
N
last 3 observation days prior to day0 (TW no) or were (TW yes), and were either provided with straw (S)
A
or not provided with straw (NS). Difference in lower case letters (a, b) shows a significant difference
D
M
between levels of either factor.
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Figure 3. The probability of having a lowered tail in the pen. Pens either had docked or undocked pigs and were either observed on days with tail biting (two observations prior to and after the recording of a bleeding
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tail wound in the specific pen) or on days without tail biting (all other observation days during the study period). Difference in lower case letters (a, b) shows a significant difference between pens with docked and
CC
undocked pigs. Difference in upper case letters (A, B) shows a significant difference between observation
A
days with and without tail biting.
19
20
D
TE
EP
CC
A
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U
N
A
M
21
D
TE
EP
CC
A
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U
N
A
M
Table 1. Number of observations (on individual pig level) scored with a tail wound (both non-bleeding and bleeding tail wounds included) and a bleeding tail wound combined with an observation of the tail tucked between the legs.
Tail wound (n)
Bleeding tail wound (n)
No
Yes
% Yes
21499
20460
1039
4.8
No
21369
20367
1002
4.7
Yes
130
93
37
28.5
Total (n)
No
Yes
% Yes
21442
57
0.3
21323
46
0.2
119
11
8.5
A
CC
EP
TE
D
M
A
N
U
Tail between legs (n)
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Total (n)
22