Introduction Materials and methods

Livestock Production Science 63 2000 121–129 www.elsevier.com locate livprodsci Aggression among finishing pigs following mixing in kennelled and unkennelled accommodation a , b ,1 a ,2 H.A.M. Spoolder , S.A. Edwards , S. Corning a ADAS Terrington , Terrington St. Clement, King’s Lynn PE34 4PW, UK b SAC Aberdeen , The Ferguson Building, Craibstone, Bucksburn, Aberdeen AB1 9YA, UK Received 3 September 1998; received in revised form 10 March 1999; accepted 17 May 1999 Abstract This study examines the interactive effects of mixing and the provision of kennels to finishing pigs on agonistic behaviour. Pigs were housed either in naturally ventilated kennelled accommodation, or in an unkennelled sloping floor accommodation with automatically controlled natural ventilation ACNV. Under each of these two housing conditions, three groups of 10 pigs were subjected to one of the following four mixing moving treatments: no mixing control, mixing and moving at 55 kg only, mixing and moving at 75 kg only and mixing and moving on both occasions. Groups which were not mixed at 55 kg or at 75 kg were moved to a novel pen at the time that the others were mixed. Mixing and moving pigs resulted in higher levels of aggression and skin damage compared to moving only. Levels of skin lesions were lower when mixing at 55 kg compared to mixing at 75 kg. The duration and frequency of fights in the immediate post mixing period and skin damage measured on day 1 after mixing correlated well when mixing pigs at 75 kg, but not when mixing at 55 kg. This suggests that the hierarchy takes longer to be established in younger pigs than it does in older heavier pigs, or that skin damage inflicted by heavier pigs during fights is more severe. Previous mixing at 55 kg had minimal effects on mixing at 75 kg in terms of behaviour immediately post mixing and skin lesions in the following two days. The presence of a kennel appeared to have a positive effect on the average duration of fights, but the effect on the proportion of fights which involved location changes lying to dunging area or vice versa was not significant. Performance data suggested that food conversion ratios were poorer in the first two weeks after mixing in the kennelled building, but not in the sloping floor building. Increased social and thermal stress after mixing in the kennelled, naturally ventilated accommodation may have been the cause of this. Over the whole of the finishing period, daily live weight gains and food conversion ratios did not differ measurably between treatments.  2000 Elsevier Science B.V. All rights reserved. Keywords : Pig; Finishers; Housing system; Aggression; Mixing Corresponding author. Present address: Praktijkonderzoek Veehouderij, Runderweg 6, 8219 PK Lelystad, The Netherlands. Tel.: 1 31-320-293-211; fax: 1 31-320-241-584.

1. Introduction

E-mail address : H.A.M.Spoolderpv.agro.nl H.A.M. Spool- der European Union EU Council Directive 91 630 1 Present address: University of Aberdeen, Department of Ag- EEC, which lays down minimum standards for the riculture, 581 King Street, Aberdeen AB24 5UA, UK. 2 protection of pigs, states that ‘‘Pigs should be kept in Present address: PIC, Fyfield Wick, Abingdon OX13 5NA, UK. stable groups with as little mixing as possible’’. This 0301-6226 00 – see front matter  2000 Elsevier Science B.V. All rights reserved. P I I : S 0 3 0 1 - 6 2 2 6 9 9 0 0 1 2 1 - 9 122 H .A.M. Spoolder et al. Livestock Production Science 63 2000 121 –129 rule has been adopted as mixing pigs almost study, this principle was tested by addressing loca- inevitably leads to aggression in order to re-establish tion changes during aggressive interactions following the dominance hierarchy in the group. Potentially, mixing. Two housing systems were used. The first the elevated levels of aggression in the group will system offered a ‘‘barrier’’ in the form of a kennel result in increased risk of death or injury, an increase wall separating a scrape through dunging passage in the number of skin lesions with associated and a strawed kennel. The other consisted of a implications for welfare and health and a reduction rectangular pen with a strawed lying area and a in growth. In practice, mixing of finishing pigs may scrape through dunging passage, and no physical occur when a change of pen becomes necessary to barrier to separate the two. The study aimed to increase space allowance as the animal grows, or investigate the effects these commercially used sys- when heavier pen mates are being marketed and the tems have on aggression in groups of finishers remaining pigs are put together in one pen. In both immediately after mixing. cases mixing will allow the producer to make better use of his facilities. The latter situation occurs primarily in the final weeks of the finishing period.

2. Materials and methods

In the present study, pigs were mixed either not at all, at a weight when pen changes may become 2.1. Treatments necessary 55 kg, just prior to slaughter 75 kg or on both occasions. This last treatment also allowed The experimental design was a 2 3 4 factorial. the hypothesis to be tested that pigs learn social The two factors under investigation were housing skills when mixed more than once see: Van Putten system and frequency of mixing. System 1 was the and Burl«, 1997; Dingemans et al., 1993. kennelled system K. Each pen had a 3.1 3 2.6 m Various methods, including mixing at different scrape through dunging area, and a 2.6 3 1.2 m straw times of the day Barnett et al., 1994; Barnett et al., bedded kennel. The building was naturally venti- 1996, the administration of tranquilising drugs e.g., lated. Pens in system 2 had an insulated 1:16 sloping Luescher et al., 1990; Tan and Shackleton, 1990 and floor S of 4.8 3 2.0 m, and a level 2.0 3 2.0 m the dimming of light from 100 to 5 lx Christison, scrape through dunging area. Straw was provided 1996 have been tested for their potential to reduce from a rack at the top of the slope. An automatically aggression during mixing. In general, these methods controlled natural ventilation ACNV system was in only showed a reduction in aggression in the initial operation, set to maintain room temperature at 17 8C. stages, by delaying the settling of the social hierar- The mixing treatments consisted of mixing pigs at chy; skin lesions between controls and treatments are either 55 or 75 kg live weight. All mixing treatments often not different in the days following mixing. In were applied by moving half the animals in a group sows, Edwards et al. 1993 used a central, sus- to one pen, and the other half to another. Animals pended barrier in a mixing pen and found that this were selected at random. They were there joined by reduced the frequency of fights. In weaners, Waran pigs from another group on the same mixing treat- and Broom 1993 found a comparable effect of an ment, to make up original numbers. Groups which opaque barrier: the frequency of aggressive interac- were not mixed were moved as a group to another tions was reduced by 40 during the first week after pen. Mixing moving at 55 kg will from here on be weaning in pens with a barrier fitted. The authors of referred to as ‘‘Mix 1’’ whereas mixing and moving both studies argue that the provision of a barrier at 75 kg will be referred to as ‘‘Mix 2’’. Table 1 allows the pig which is attacked to disappear out of explains the four resulting mixing treatments. the view of the aggressor, thereby ‘‘solving’’ the dispute effectively, with a minimum of interactions. 2.2. Animals and management Other authors failed to confirm this hypothesis by looking at aggression and skin lesions in pens with Animals were allocated to their treatments in artificial partitioning e.g., weaners: Olesen et al. groups of 14 at an approximate average live weight 1996; gilts: Luescher et al. 1990. In the present of 30 kg. Mix 1 was applied at 55 kg, at which time H .A.M. Spoolder et al. Livestock Production Science 63 2000 121 –129 123 Table 1 2.3. Observations The four mixing treatments applied in each of the two housing systems Data were collected on behaviour, skin lesions and At 55 kg Mix 1 At 75 kg Mix 2 daily live weight gain of the animals in the post- Treatment C control Moving only Moving only mixing period. Treatment A Mixing and moving Moving only Treatment B Moving only Mixing and moving 2.3.1. Behaviour Treatment D Mixing and moving Mixing and moving Behaviour observations were carried out on four focal pigs in each group of 10 two male, two the size of the group was reduced to 10 pigs half female. These four pigs were selected on the basis male, half female. The initially larger group size that their weight was as close as possible to the was necessary to avoid potential thermal problems average of the group. Ad libitum sampling, a tech- due to under stocking the building when pigs were nique which records all instances of a particular type small, and to allow for any pigs dropping out prior to of behaviour and the circumstances related to it the start of the treatments. Pigs were sold at an Martin and Bateson, 1993 was used. In the present approximate average live weight of 85 kg. Each of study, all aggressive interactions involving any of the the eight treatments had three replicate pens, giving a four focal animals were recorded see Table 2. In total of 24 pens 240 animals. During the experi- addition, activity levels active inactive and location ment pigs were fed ad libitum from a single space lying area dunging area of focal animals were hopper. Water was provided ad libitum. Straw was recorded on a continual basis. The observation available to animals on the S treatments from a straw periods started immediately after the moving and hopper, which was topped up daily. Pigs on the K mixing treatment was applied, and lasted for 2 h. treatment were given half a bale of straw per pen per Husky Hunter16 computers, mounted with the be- day. One third of this straw was put into the kennel, haviour observation package Observer 2000 Noldus, and the rest was used to replace the scraped out Wageningen, The Netherlands were used to collect straw in the dunging passage. the data. Table 2 Scoring system for aggressive interactions Behaviour Description K Knock or threat ]]]] The challenge consists of little more than thrust or a knock with closed mouth by the initiator, which the recipient either ignores, or responds to with a similar reaction B Bite ] The challenge is a bite and or the recipient responds with a single bite after which the interaction is resolved O One-sided fight ]]]] The challenge results in a series of bites from either the initiator or the recipient, showing a complete control of one animal over the situation T Two-sided fight ]]]] The challenge is not resolved immediately and a prolonged fight determines the eventual winner I Inactive ]] The animal is asleep or inactive A Active ]] The animal is active, but not involved in an aggressive interaction 124 H .A.M. Spoolder et al. Livestock Production Science 63 2000 121 –129 2.3.2. Skin damage housing system. Tukey’s HSD was used for pair- Skin damage was assessed on focal animals on the wise comparison of the means of the treatments day before each of the two mixing moving treat- Minitab, 1993. Strong tendencies 0.05 , P , ments were applied, on the day after mixing, at day 7 0.10 have also been indicated in the tables. after Mix 1 and on day 5 after Mix 2. The assess- ment consisted of a count of the number of skin lesions bruises, scratches and wounds per area:

3. Results