Computers and Electronics in Agriculture 99 (2013) 209–217

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Computers and Electronics in Agriculture

journal homepage: www.elsevier .com/locate /compag

Analysis of aggressive behaviours of pigs by automatic video recordings

0168-1699/$ - see front matter � 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.compag.2013.09.015

⇑ Corresponding author at: Fancom Research, Panningen, Industrieterrein 34,5981 NK Panningen, The Netherlands. Tel.: +31 77 306 96 00, mobile: +31619112799; fax: +31 77 306 96 01.

E-mail address: moczak@fancom.com (M. Oczak).

Maciej Oczak a,b,⇑, Gunel Ismayilova c, Annamaria Costa c, Stefano Viazzi b, Lilia Thays Sonoda d,Michaela Fels d, Claudia Bahr b, Jörg Hartung d, Marcella Guarino c, Daniel Berckmans b, Erik Vranken a,b

a Fancom Research, Panningen, Industrieterrein 34, 5981 NK Panningen, The Netherlandsb M3-BIORES: Measure, Model, Manage Bioresponses, Katholieke Universiteit Leuven, Kasteelpark Arenberg 30, B-3001 Leuven, Belgiumc Department of Health, Animal science and Food Safety, Faculty of Veterinary Medicine, Università degli Studi, via Celoria 10, 20133 Milan, Italyd University of Veterinary Medicine Hannover, Foundation, Institute for Animal Hygiene, Animal Welfare and Farm Animal Behaviour, Buenteweg 17p, 30559 Hannover, Germany

a r t i c l e i n f o

Article history:Received 30 July 2012Received in revised form 26 September 2013Accepted 30 September 2013

Keywords:PigsAggressionBehaviourPhases

a b s t r a c t

Aggression among pigs in today’s production systems results in negative impact on health and welfare ofanimals as well as on productivity of the systems. Precision Livestock Farming technology might poten-tially offer a possibility to monitor and reduce the level of aggression and hence its negative impact. Thispaper reports about the initial part of a larger study investigating the possibilities of applying continuousautomatic monitoring of aggressive behaviour among pigs. It investigates how behavioural patterns inpig’s aggressive behaviour can be identified and utilized in order to predict severe forms of aggression(biting) expressed in later phases of aggressive interactions.

An experiment was carried out at a commercial farm on a group of 11 male pigs weighing on average23 kg and kept in a pen of 4 m � 2.5 m. During the first 3 days after mixing in total 8 h of video recordingwere registered with a top view camera for later analysis of animal behaviour. As a result of labelling ofthe video recordings, 157 aggressive interactions were identified with 12 behaviour types expressed for860 times within the interactions. The identified interactions were divided into interactions that led tobiting and those that did not lead to biting behaviour. The interactions that led to biting behaviouraccounted for 36.3% (57) of all aggressive interactions while interactions that did not lead to bitingbehaviour were 63.7% (100) of the interactions. The average duration of initiating (nosing) phase ofaggressive interactions (3.32 s) lasted longer (P < 0.05) in interactions that led to biting behaviour thanin interactions that did not lead to biting behaviour (1.94 s). The next phase of aggressive interactions– medium phase – similarly to initiating phase, lasted on average longer (18.21 s) (P < 0.01) in interac-tions that led to biting behaviour than in interactions that did not lead to biting behaviour (16.15 s). Withthe differences found between interactions that led and did not lead to biting behaviour it seems to bepossible to discriminate between both types of interactions in an early phase of aggression. The differ-ences found might serve as early signs in a management support system that aims to prevent severeforms of aggressive behaviour (biting) among pigs.

� 2013 Elsevier B.V. All rights reserved.

1. Introduction

The social organization of domesticated pigs, sus scrofa, livingunder farm conditions is, as in wild pigs, based upon a dominancehierarchy (McBride et al., 1964). Hierarchy develops as a part ofpig’s social life and is a form of group organization. Establishmentof social hierarchy results in division of a group of pigs to sub-groups of dominants, subdominants, submissive, subordinate andmarginal. Two types of dominance hierarchy can develop in a

group of pigs: a linear order or a triangle type (Hafez, 1975). Inthe latter case individual pigs differ less in social position.

If piglets originating from at least two different litters areweaned into one pen then hierarchical order is formed. The prac-tice can result in intense aggression which continues mainlythroughout the first 24–48 h after a new group of animals is com-posed, thus when the dominance hierarchy is being established(Marchant-Forde, 2010). A new hierarchical order develops alwayswhen a composition of a group of pig’s changes, therefore forexample when pigs are mixed during transfer to the older agegroups (Keeling and Gonyou, 2001).

Conditions in confined environment can cause dominance hier-archy to be less successful in controlling aggression within thegroup, increasing the incidence of aggressive behaviour through-out pig’s group life (Ewbank and Bryant, 1969). The conditions

210 M. Oczak et al. / Computers and Electronics in Agriculture 99 (2013) 209–217

are: limited space allowance (Jensen, 1984), competition for feed(Walker, 1995), barren environment (Durrell et al., 1997), low fibrefeed composition, (Meunier-Salaun et al., 2001).

An elevated aggression level has negative impact on health,welfare (McGlone et al., 1981; Marchant-Forde, 2010) and produc-tivity of pigs (Stookey and Gonyou, 1994; Arey and Edwards,1998). The idea of reducing aggression level among pigs in confine-ment was investigated by many researchers. The following meth-ods were tested: application of sedatives (Tan and Shackleton,1990), odour masking agents (Barnett et al., 1993), provision ofenvironmental enrichment (Melotti et al., 2011; Waran and Broom,1993; McGlone and Curtis, 1985; Schaefer et al., 1990), increase ofspace allowance (Gonyou et al., 2006), change of dry feeding sys-tem to wet (Andersen et al., 1999), increase amount of fibre insow’s diet (Meunier-Salaun et al., 2001).

Possibilities of Precision Livestock Farming technology in rela-tion to the problem of aggression have not been explored yet andmight offer a new possibility to effectively lower aggression levelamong pigs. Precision Livestock Farming (PLF) is defined as themanagement of livestock production using the principles and tech-nology of process engineering. PLF relies upon automatic monitor-ing of livestock and related physical processes (Wathes et al.,2008). PLF is currently regarded as the heart of the engineeringendeavour towards sustainability in (primary) food production.Its application allows making optimal use of knowledge and infor-mation in the monitoring of processes (Berckmans, 2008).

This paper aims to be an initial step in creating an automaticmonitoring system of pigs aggression. The focus of the article isto perform human eye observation and analysis in a way that theresults could be used in the next steps for development of the auto-matic system.

The basic studies on pig aggressive behaviour performed byMcGlone (1985) revealed that it is a complex and gradual behav-iour. The fight breaks out gradually as the pigs investigate eachother using a series of specific and often reciprocal behaviours,characterized by nosing, sniffing and gentle nudging. This maythen escalate into more vigorous pushing, pressing, bites andhead-knocking, out of which biting is considered to be the mostdamaging (Turner et al., 2006). Thus, as the fight progresses, theintensity increases which means that more damaging behavioursoccur more frequently later in the fight. The last phase of aggres-sive interactions consists of direct sampling of actual fighting abil-ity, through overt, dangerous fighting (Jensen and Yngvesson,1998). Therefore our hypothesis is that identification of patternsin sequences of specific behaviours and understanding the gradualdevelopment of aggressive behaviour should allow automatedmonitoring and prediction of aggressive behaviour expressed inthe final phase of these interactions. In order to monitor thesebehaviours with an automatic monitoring system we defined thefollowing objectives for this study:

� Identification of differences between aggressive interactionsleading to biting behaviour and those that do not lead to thisbehaviour.

� Identification of early signs of biting behaviour on the basis ofbehavioural patterns occurring within aggressive interactions,before biting behaviour.

2. Materials and methods

2.1. Animals and housing

In order to achieve the objectives of the study behaviouralobservations were carried out. The observations were carried outat a commercial farm, located in Heusden, the Netherlands, witha capacity of approximately 6000 fattening pigs (Topigs 20 (large

White � Landrace) � Pietrain) weighing from 23 to 120 kg. Elevennon-castrated male pigs, weighing 23 kg on average were observedin a pen sized 4 m � 2.5 m. The pen was surrounded by solid, plas-tic wall. A floor of the pen was constructed from concrete. Half ofthe pens floor was slatted while the other half was solid, barrensurface. The pigs used in the experiment were originating from 4different pens (3 + 3 + 3 + 2 pigs) and were mixed immediately be-fore the observation started. The pigs were fed ad libitum with adry feeding system at one feeder with two feeding places. The fee-der was located in the front part of the pen, near the corridor of acompartment from where the observations were performed. Asource of drinking water in form of a metal drinker was installedon the feeder’s wall. Air exchange was provided by a mechanical,central flow ventilation system. A source of light in the compart-ment was two windows (each 1 � 1 m) and six 100 Watt fluores-cent tubes. In time of observations artificial lighting was turnedon. Natural and artificial lighting provided illuminance of 50 luxin the observed pen. Pigs were individually marked by standardcolour stock marker spray on their backs in order to identify indi-viduals on the video recordings.

2.2. Experimental installations

The video recordings were registered using a camera (Allied Vi-sion Technologies�, model F080C) with 4.8 mm lens, placed abovethe pen in central position at a height of 2.3 m, that permitted a topview of the whole pen. Colour images were captured with a framerate of 11 frames per second and a resolution of 1032 � 778 pixels.The videos were stored in a computer for later analysis. A total of8 h of video recordings were registered in this way during the first3 days after mixing (day 1: 2 h, day 2: 3 h, day 3: 3 h). In the firstday of the observations the recordings were registered from11.00 to 13.00 o’clock, on the second and third day from 11.00 to14.00 o’clock. The reason for shorter period of observation on thefirst day of the trial was technical problems experienced on thefarm.

2.3. Labelling procedure

Video recordings registered by the camera during the experi-ment were labelled by human observer according to a video label-ling procedure. The procedure consisted of a labeller watching thevideo recordings and noting his observations. Interactions wereobserved on the video images frame by frame to determine the ex-act starting frame and time and duration of the aggression and todescribe the pig’s behaviour within aggressive interactions.Recordings were captured at a frame rate of 11 frames per second,which translates to 316,800 frames in 8 h of video material(1 min = 60 s, 1 h = 3600 s, 8 h = 28,800 s and 28,800 s � 11frames = 316800 frames). It took approximately 90 men hours tolabel 8 h (316,800 frames) of video recordings. It was only possibleto label the behaviours on the video recordings with a precision of1 s. Behaviour in order to be classified by the labeller as a behav-ioural event had to be performed by animals for at least 1 s (Jensenand Yngvesson, 1998).

Behaviours chosen to be labelled in video labelling procedurewere: nose to nose interaction, head to head knocking, head tobody knocking, inverse parallel pressing, parallel pressing, neckbiting, body biting, ear chewing, jump on other, aiming, chasingand walking, as reported in Table 1.

Within behaviours listed above head to head knocking, head tobody knocking, inverse parallel pressing, parallel pressing, aiming,neck biting, body biting and chasing were categorized as aggres-sive behaviours. Nose to nose and ear chewing behaviours werecategorized as interaction behaviours, jump on other as sexualbehaviour, walking as locomotion behaviour (Table 1). Behaviour

Table 1Behaviours labelled.

Behaviourcategory

Behaviour name Description

Aggressive Head to headknocking

Hitting with the snout against the head of the receiver (Keeling and Gonyou, 2001; Fraser, 1974)

Head to bodyknocking

Hitting with the snout against the body of the receiver (Keeling and Gonyou, 2001; Fraser, 1974)

Parallel pressing Pressing of shoulders against each other, facing same directions (Keeling and Gonyou, 2001; Fraser, 1974)Inverse parallelpressing

Pressing of shoulders against each other, facing opposite directions (Keeling and Gonyou, 2001; Fraser, 1974)

Neck biting Biting neck of another pig without head trusting (O’Connell et al., 2005)Body biting Biting body of another pig without head trusting (O’Connell et al., 2005)Aiming An upward-directed trust of the snout, slightly directed at the receiver, from a distance of 2–3 m. (Keeling and Gonyou, 2001;

Fraser, 1974)Chasing Following another pig in quick pursuit, usually biting or trying to bite (Erhard et al., 1997)

Interaction Nose to nose The nose approaches the snout or head of the receiver. (Keeling and Gonyou, 2001; Fraser, 1974)Ear chewing Chewing movements while the ear of a pen mate is in the mouth (Jensen et al., 2010)

Sexual Jump on other(mounting)

Jump with front legs on another pig (McGlone, 1985)

Locomotion Walking A symmetrical gait of medium speed in which the pig is supported by alternating diagonal pairs of legs. The sequence of legmovements is left front and right hind, then right front and left hind (Fraser and Broom, 1998)

M. Oczak et al. / Computers and Electronics in Agriculture 99 (2013) 209–217 211

categories were not quantified and thus no analysis on behaviouralcategories was carried out. The analysis was carried out on behav-iour types, which were quantified as events in terms of frequencyand duration.

Data obtained as a result of the labelling procedure were care-fully analysed in order to identify patterns in pig’s aggressivebehaviour. An aggressive interaction was defined as a series ofaggressive and non-aggressive behaviours following one after an-other, between at least two pigs (Table 1). The interaction was la-belled as finished when pigs lost physical contact with each otherfor at least one second and redirected their attention to the otherpen mates and/or elements of the pen.

In the video labelling procedure, aggressive interactions weredivided into 3 phases: initiating phase (nosing phase), mediumaggression phase and high aggression phase (biting phase)(Table 2). The division on the three phases was based on timingof occurrence of the behaviours within interactions. Nose to noseinteraction, ear chewing and jump on other behaviours were de-fined as the behaviours that initiate aggressive interactions. Thesebehaviours were labelled as part of the initiating phase (nosingphase) of aggressive interactions. Head to head knocking, head tobody knocking, inverse parallel pressing, parallel pressing and aim-ing behaviours were defined as initiating medium aggressionphase. The medium aggression phase was expected to follow nos-ing phase of aggressive interactions. A high aggression phase (bit-ing phase) was defined as initiated by neck biting or body bitingbehaviours and was expected to occur at the end of aggressiveinteractions. Additionally behaviours that directly followed up aninteraction (were expressed in the next second) were labelled.

Non-aggressive behaviours, in order to be classified as part ofaggressive interactions, had to be exchanged between pigs stayingin close physical contact, in-between aggressive behaviours (one

Table 2Overview of behaviours that initiated three phases of aggressive interactions.

Initiating (nosing) phase Medium phase High (biting) phase

Nose to nose interaction Head to head knocking Neck bitingEar chewing Head to body knocking Body bitingJump on other Inverse parallel pressing –– Parallel pressing –– Aiming –

second before or after aggressive behaviours), between the samepair of pigs.

The three phases of aggressive interactions together with non-aggressive behaviours that occurred in between the phases wereaccounting for the total time of aggressive interactions.

2.4. Statistical analysis

Behaviour data were first collated and the frequencies of occur-rence of aggressive interactions that led to biting and did not leadto biting behaviour were expressed as percentage of the total num-ber of aggressive interactions. As the data collected during theobservations were not normally distributed we decided to statisti-cally test them with the Kruskal–Wallis test. The test is non para-metric and does not assume normal distribution. The total averageduration of aggressive interactions that led to biting and that didnot lead to biting behaviour as well as the differences in the aver-age duration of initiating (nosing) phase and medium aggressionphase of the interactions were compared with the Kruskal–Wallistest. The frequencies of occurrence of aggressive interactions thatled to biting and did not lead to biting behaviour were comparedwith the same test (Kruskal–Wallis) (Matlab).

3. Results

In the pen with 11 pigs, a total of 157 aggressive interactionswere observed during the observation period of 8 h. Out of which100 (63.7%) were classified as interactions that did not lead to bit-ing behaviour (neither neck nor body) and 57 (36.3%) were classi-fied as interactions that led to biting behaviour (Table 3). Theaverage duration of interactions (38.82 s) that led to biting behav-iour (neck or body) was longer (P < 0.01) than the average duration

Table 3Number of aggressive interactions.

Type of interactions Number of interactions

N Percentage

Interactions that did not lead to biting 100 63.7Interactions that led to biting 57 36.3Total 157 100.0

P > 0.05.

Table 4Overview of duration of aggressive interactions, initiating (nosing) phase, medium phase and high (biting) phase.

Name Interactions that led to biting Interactions that did not lead to biting

Mean (s) SEM (s) Mean (s) SEM (s)

Duration of interactions 38.82 A 5.73 18.09 B 4.32Duration of initiating (nosing) phase 3.32 a 0.61 1.94 b 0.46Duration of medium phase 18.21 A 4.74 16.15 B 3.68Duration of high (biting) phase 17.29 2.93 – –

Significant differences are indicated by different letters: A and B – P < 0.01; a and b – P < 0.05.

Fig. 1. Duration of aggressive interactions that did not lead to biting.

Fig. 2. Duration of aggressive interactions that led to biting.

Fig. 3. Behaviours that occurred at the beginning of all aggressive interactions.

Fig. 4. Behaviours that occurred at the beginning of aggressive interactions that didnot lead to biting.

212 M. Oczak et al. / Computers and Electronics in Agriculture 99 (2013) 209–217

of interactions that did not lead to this behaviour (18.09 s)(Table 4). The order of occurrence of three phases of aggressiveinteractions was in each interaction registered as: first initiatingphase, second medium aggression phase and third high aggressionphase. The average duration of the initiating (nosing) phase ofaggressive interactions (3.32 s) lasted longer (P < 0.05) in interac-tions that led to biting behaviour than in interactions that didnot lead to biting behaviour (1.94 s) (Table 4).

The next phase of aggressive interactions – the medium phase –similarly to initiating phase, lasted on average significantly longer(18.21 s) (P < 0.01) in interactions that led to biting behaviour than

in interactions that did not lead to biting behaviour (16.15 s)(Table 4). The average duration of the last phase of aggressive inter-actions – high (biting) phase – was recorded as 17.3 s (Table 4).

Fig. 5. Behaviours that occurred at the beginning of aggressive interactions that ledto biting.

Fig. 6. Behaviours that occurred within all aggressive interactions.

Fig. 7. Behaviours that occurred within aggressive interactions that did not lead tobiting.

Fig. 8. Behaviours that occurred within aggressive interactions that led to biting.

M. Oczak et al. / Computers and Electronics in Agriculture 99 (2013) 209–217 213

The number of relatively short aggressive interactions thatlasted for 5 s or less constituted to 37% of interactions that didnot lead to biting behaviour (Fig. 1). In interactions that led to bit-ing behaviour short interactions accounted for 15.8% (Fig. 2). Verylong aggressive interactions that lasted for more than 1 min ac-counted for 17.5% of interactions that led to biting behaviour(Fig. 2) and for 7% in interactions that did not lead to this behaviour(Fig. 1). Aggressive interactions started the most often with nose tonose interaction (45.9%) and head to head knocking behaviours(43.3%) (Fig. 3). In interactions that did not lead to biting behaviourhead to head knocking was the most often interaction initiatingbehaviour (53.0%) (Fig. 4). Aggressive interactions that led to bitingbehaviour were started with the highest frequency with nose tonose interaction (59.6%) (Fig. 5).

The analysis of order of occurrence of aggressive behaviourswithin aggressive interactions revealed that biting behaviour was

registered as on average 5.7 out of 6.7 behaviours. Thus bitingbehaviour was a behaviour that was expressed by pigs as one ofthe last in the observed interactions.

The frequency and duration of all 12 categorized behavioursthat occurred within aggressive interactions (Table 1) were calcu-lated. The result revealed that the 12 behaviour types occurred 860times in total, within all aggressive interactions (Fig. 6). Out ofwhich head to head knocking behaviour was the most often occur-ring behaviour in both types of interactions (53.6% and 29.4%)(Figs. 7 and 8). In interactions that led to biting behaviour, the neckbiting behaviour was calculated to account for 22.7% of all thebehaviours that occurred within this type of interactions (Fig. 8).

Labelling of behaviours that occurred directly after aggressiveinteractions, revealed that out of 157 interactions in total, 11 weredirectly followed up by interaction with another pig. Neck bitingbehaviour was the most (6) often occurring behaviour directlyafter aggressive interaction (Table 5).

Involvement of individual pigs in aggressive interactions varied.Pigs were involved in aggressive interactions during the 8 h period

Table 5Behaviours that occurred directly after aggressive interactions.

Type of interactions Walking Neck biting Ear manipulation. Nose to nose interaction Ear manipulation

N Percentage Meanduration(s)

N Percentage Meanduration(s)

N Percentage Meanduration(s)

N Percentage Meanduration(s)

N Percentage Meanduration(s)

Interactions that did notlead to biting

98 67.1 18.19 – – – 1 50.0 24.00 1 50.0 2.00 – – –

Interactions that led tobiting

48 32.9 42.96 6 100.0 18.00 1 50.0 12.00 1 50.0 8.00 1 100.0 23.00

Total 146 100.0 26.34 6 100.0 18.00 2 100.0 18.00 2 100.0 5.00 1 100.0 23.00

Table 6Participation of individual pigs in aggressive interactions.

Pignumber

All aggressive interactions Interactions that did not lead to biting Interactions that led to biting

N Percentage Meanduration (s)

Total duration(min)

N Percentage Meanduration (s)

Totalduration (s)

N Percentage Meanduration (s)

Total duration(min)

1 53 16.9 27.96 24.42 35 17.5 18.2 637 18 15.8 46.94 14.052 19 6.1 13 4.07 15 7.5 8.2 123 4 3.5 31 2.043 22 7.0 27.23 9.59 9 4.5 8.22 74 13 11.4 40.38 8.454 6 1.9 32.83 3.17 2 1.0 22 44 4 3.5 38.25 2.335 15 4.8 21.13 5.17 9 4.5 11.11 100 6 5.3 36.17 3.376 41 13.1 54.22 37.03 25 12.5 37.12 928 16 14.0 80.94 21.357 60 19.1 14.02 14.01 48 24.0 10 480 12 10.5 30.08 6.018 16 5.1 14.13 3.46 8 4.0 9.25 74 8 7.0 19 2.329 19 6.1 18.26 5.47 10 5.0 16 160 9 7.9 20.78 3.07

10 14 4.5 11.43 2.40 7 3.5 13 91 7 6.1 9.86 1.0911 49 15.6 28.67 23.25 32 16.0 28.34 907 17 14.9 29.29 8.18

Total 314 100 263 2.14.04 200 100 181 3618 114 100 383 1.13.46

214 M. Oczak et al. / Computers and Electronics in Agriculture 99 (2013) 209–217

for from 2 min 40 s (pig 10) to 37 min 3 s (pig 6). On average oneaggressive interaction was lasting from 11.43 s (pig 10) to 54.22 s(pig 6) (Table 6). The pig that was participating in behaviours de-fined as part of aggressive interactions for the longest time waspig number 6 (37 min 3 s). The pig expressed the following behav-iours for the longest time in comparison to the other pen mates:inverse parallel pressing (8 min 54 s), walking (7 min 23 s), noseto nose interaction (6 min 41 s), neck biting (6 min 39 s), head tohead knock (6 min 10 s), parallel pressing (41 s) and body biting(18 s) (Table 7). The pig that was involved in the highest numberof aggressive interactions was pig number 7 (60 interactions)(Table 6).

4. Discussion

One of the objectives of our study was to identify aggressiveinteractions leading to damaging biting behaviour. We found thatbiting was a behaviour that was expressed by pigs as one of the lastin the observed interactions.

McGlone (1985) described aggressive and submissive behav-iours during normal and complete fights of newly regrouped pre-pubertal swine. The author divided a fight into three phases andfound out that most bites occurred in the third (last) phase ofthe fight. Our results are in accordance with McGlone’s (1985)findings as biting behaviour was on average occurring as 5.7 outof 6.7 behaviours within aggressive interactions. These findingssuggest that if identifiable patterns within pig’s aggressive behav-iour exist, then it should be possible to predict biting behaviourand intervene before the behaviour occurs. Jensen (1980) firstidentified social behaviours and then applied an analysis of se-quences of behaviour to determine which aggressive sequences oc-curred at a greater-than-random frequency. Jensen in his laterstudy together with Yngvesson (1998) divided a fight into twophases: nosing phase and biting phase. Nosing phase included

exchange of mutual nose contacts, mostly directed towards head,ears and snout of the opponent, while the pigs were walking closetogether. Biting phase consisted of mutual biting towards head,ears, neck and flank of the opponent, and pushing with flanksagainst each other. In 65 of the 74 pairs (87.8%) confronted inthe experiment, the contest escalated to overt fighting (bitingphase) while in 9 out of 74 pairs (12.2%) confrontations ended upin the nosing phase. Results of our observations revealed that63.7% of the observed interactions did not lead to biting behaviourand that 36.3% of interactions contained this behaviour. The firstreason for the difference in the results between Jensen and ourfindings could be that biting phases were defined differently inboth experiments. Jensen and Yngvesson (1998) defined bitingphase as a sequence of mutual biting towards head, ears, neckand flank of the opponent, and pushing with flanks against eachother. While in our observations biting phase was defined as aphase that was initiated by neck or body biting behaviours. Thesecond reason for observed difference is that in Jensen’s andYngvesson’s (1998) experiment pairs of pigs (only 2 pigs simulta-neously) were confronted in a test arena (2.5 � 1.5 m) and ob-served until the contests between pigs were finished. During ourobservations pigs were freely interacting with 10 pen mates, thuswe registered aggressive interactions under practical farming con-ditions which included initial encounters between different pigs aswell as following aggressive interactions.

In our observations ‘‘nose to nose interaction’’ was the behav-iour that started aggressive interactions the most often (45.9%).Jensen (1982) interpreted nose to nose interaction initially as aneutral behaviour, associated with individual recognition. How-ever, statistical inhibition of nose to nose interaction towards ‘‘noreaction’’, together with the directive effects towards ‘‘head-to-head knock’’, made it more logical for Jensen to eventually con-clude in the paper (1982) that the ‘‘nose-to-nose’’ has a slightaggressive tendency, perhaps being a mild threat. This was also

Tabl

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ing

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031

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624

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584.

0710

29.

5941

3.17

525.

1739

137

.03

254

14.0

160

3.46

835.

4750

2.40

293

23.2

5

M. Oczak et al. / Computers and Electronics in Agriculture 99 (2013) 209–217 215

indicated by the fact that ‘‘nose-to-nose’’ was mainly initiated bydominant (not-avoiding) animals. Jensen and Yngvesson (1998)found that nose to nose phase of aggressive interaction – definedas exchange of mutual nose contacts, mostly directed towardshead, ears and snout of the opponent – was significantly shorterfor pre-exposed pairs of pigs (pigs were familiar with each other).This finding suggests that the behaviour’s main function might berecognition of pen mates. Therefore when a pig was already famil-iar with another pig it required less time to recognize a pen mate.In our research initiating phase (nosing phase) of aggressive inter-actions was lasting more time (3.32 s) (P < 0.05) in interactionsthat led to biting behaviour (neck or body) than in interactions thatdid not lead to biting (1.94 s). Moreover the interactions that led tobiting behaviour started very often with nose to nose interaction(59.6%). Based on these results we conclude that interactions thatdo not lead to biting behaviour usually occur when pigs are morefamiliar with each other and already recognize pen mates fightingability. Then the hierarchy is maintained by threats, avoidanceand withdrawal, or short-lived aggressive interactions(Marchant-Forde, 2010), usually without expression of bitingbehaviour (Fraser, 1974).

The next phase of an aggressive interaction that was identifiedin our observations was a phase named medium aggression phase.The aggressive behaviours that we included in this phase of aggres-sive interactions were: head to head knocking, head to body knock-ing, inverse parallel pressing, parallel pressing and aiming. Thesebehaviours are generally interpreted as aggressive acts (McGlone,1985; Jensen, 1980, 1982, 1994; Jensen and Yngvesson, 1998)but without physical consequences to pigs (Turner et al., 2006).Jensen and Yngvesson (1998) included these aggressive behavioursas a part of a biting phase. Therefore the biting phase in Jensen’sand Yngvesson’s study contained all the aggressive behaviours ob-served by the authors excluding ‘‘nose to nose interaction’’ whichwas defined as a part of nosing phase. In our experiment the aver-age duration of a medium aggression phase was on average longer(18.21 s) (P < 0.01) in interactions that led to biting behaviour thanin interactions that did not lead to biting behaviour (16.15 s). Lev-els of fighting can be highly variable (Oldigs et al., 1992). Fightshave been reported to last 8 min 11 s for weaned pigs (Rushenand Pajor, 1987); 1 min 58 s and 1 min 38 s for growing pigs(McGlone, 1985; Arey and Franklin, 1995); and between 1 s and3 min for sows (Mount and Seabrook, 1993). According to Bolhuiset al. (2005) fights between weaned pigs lasted on average from15.2 s to 23.2 s depending on individual copying characteristicsof individuals. In our observations duration of interactions(38.82 s) that led to biting behaviour (neck or body) was longer(P < 0.01) than of interactions that did not lead to this behaviour(18.09 s). On average one aggressive interaction was lasting from13 s to 54 s. Aggressive interactions were directly followed up byinvolvement in interaction with another pig in 11 out of 157sequences.

With the three differences found between interactions that ledand did not lead to biting behaviour it seems to be possible to dis-criminate between both types of interactions in an early phase. Thedifferences found might serve as early signs in a management sup-port system that aims to prevent severe form of aggressive behav-iour (biting) among pigs.

The results of the research could potentially be applied in a PLFsystem. There are several potential advantages of using PLF tech-nology in relation to the problem of aggression among pigs. PLFtechnology can aid a task of gathering information about the ani-mals behaviour, even with large flocks or herds (Frost et al.,1997). Sensors are not restricted to the sensory modalities of hu-man observing pigs: infra-red thermography can provide novelinformation about animal temperature, for example. The commonfeatures of sensors used in PLF are continuous, simultaneous

Fig. 9. Aggression monitoring by PLF.

216 M. Oczak et al. / Computers and Electronics in Agriculture 99 (2013) 209–217

measurement on a large number of units with analysis of temporaltrends as well as point statistics (Wathes et al., 2008). A low costcamera can be used to quantify animal’s behaviour (De Wetet al., 2003). By application of image analysis into animal observa-tion (PLF technology) it is possible to use an animal as a sensor. Themethod has the following advantages (Bloemen et al., 1997):

� The animals will not be disturbed by the measurements.� There is no physical contact with the animals, and the stress on

the animals will not, therefore, be increased.

Continuous, real time measurement of aggressive behaviour ofpigs should in the first instance allow creating an objective andaccurate information system that a farmer can use in order to re-duce the aggression on his farm. In the second instance it shouldgive a possibility to automatically lower the aggression level byapplication of actuator (i.e. sound, smell) that will change pig’sbehaviour and thus aggression level would be reduced (Fig. 9).

5. Conclusions

The aim of our study was to identify differences betweenaggressive interactions that led to highly damaging biting behav-iour and those that did not lead to this behaviour. The secondobjective of the observations was to identify early signs of highlydamaging biting behaviour on the basis of behavioural patternsthat occurred within aggressive interactions, before bitingbehaviour.

We identified several differences between aggressive interac-tions that led to biting and did not lead to biting behaviour. Thefirst difference was in the average duration of initiating phase (nos-ing phase) of aggressive interactions. Initiating phase (nosingphase) was lasting on average more time (3.32 s) (P < 0.05) ininteractions that led to biting behaviour (neck or body) than ininteractions that did not lead to biting (1.94 s). The second differ-ence was in the average duration of medium aggression phase.The duration of medium aggression phase was on average longer(18.21 s) (P < 0.01) in interactions that led to biting behaviour thanin interactions that did not lead to biting behaviour (16.15 s). Thethird difference was in the average duration of the total time ofaggressive interactions. The average duration of aggressive interac-tions that led to biting behaviour (neck or body) was longer(38.82 s) (P < 0.01) than of interactions that did not lead to thisbehaviour (18.09 s). With the three differences found betweeninteractions that led and did not lead to biting behaviour it seemsto be possible to discriminate between both types of interactions inan early phase. The differences found might serve as early signs ina management support system that aims to prevent severe form ofaggressive behaviour (biting) among pigs.

Acknowledgments

This research is a part of the BioBusiness Project and made pos-sible by the support of the EU Commission and Marie Curie InitialTraining.

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