| Hardcopy Reference: |
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| Title: |
A comparative view on social hierarchy formation at different stages of pig production using sociometric measures |
| Author(s): |
Puppe, Birger, Jan Langbein, Jörg Bauer, Steffen Hoy |
| Publication Year: |
2008 |
| Reference: |
Livestock Science 113 (2008) 155–162 |
| Country: |
Germany |
| Summary: |
The social structure of domestic pigs is based on a dominance hierarchy that is established after vigorous fighting when unacquainted pigs are brought together (Meese and Ewbank, 1973; Puppe and Tuchscherer, 1994). Amongst newly acquainted pigs mutual recognition during aggression seems to be related to an acquired familiarity (Puppe, 1998; Stookey and Gonyou, 1998), although the mechanisms underpinning individual discrimination remain rather unclear (McLeman et al., 2005). The decrease in aggression after mixing may be caused by an increase of simple habituation or, more obviously, by an increase of the clarity of mutual dominance relationships (Rushen, 1988; Jensen and Yngvesson, 1998). The repeated regrouping which is common in pig production, however, means that new hierarchies have to be established frequently. It is well known that high rates of aggression are involved in this process, which in turn may cause serious problems in animal welfare and performance (e.g. Stookey and Gonyou, 1994; Puppe and Tuchscherer, 1994; Puppe et al., 1997; Gonyou, 2001). A standardised and comprehensive approach to describe dominance relationships in gregarious farm animals quantitatively was recently developed, incorporating a combination of appropriate sociometric measures. The present study applied this approach to a comparative analysis of the social hierarchies within 57 groups of domestic pigs at different age/production stages with a total of 496 animals. Unacquainted pigs were grouped to three age categories that correspond to the typical production stages: weaned pigs (PIG28, 12 groups), growing pigs (PIG80, 16 groups), and reproductive sows (SOW, 29 groups). Based on observed agonistic interactions, sociometric values were calculated both at the dyadic and at the group level and may be considered as preliminary reference values for further studies. As indicated by the respective values of the Kendall index (PIG28: 0.66, tested as significant in 69.0% of the observed groups; PIG80: 0.71, 87.5%; SOW: 0.61, 69.0%), and the improved Landau index (PIG28: 0.70, 75.0%; PIG80: 0.72, 93.7%; SOW: 0.71, 72.4%), a social organisation towards a quasi-linear social hierarchy was predominantly developed throughout all age/production categories. However, compared to weaned and growing pigs, sows were characterised by significant differences concerning establishment (fewer agonistic interactions) and kind (more unknown dyads, fewer two-way and significant dyads, higher directional consistency index) of their social hierarchy. It seems that sows have effectively adapted their agonistic behaviour towards pen-mates to regulate social dominance relationships, whereas younger pigs frequently display agonistic interactions also to gain additional experience on social cues (e.g. the fighting ability of an opponent). Hence, it is concluded that the effective experience of socialisation during sensitive periods may increase the social skills of pigs which in turn can improve their welfare and health, e.g. by adjusted aggressive behaviour. The consideration of comparable and standardized sociometric measures in livestock breeding may help to improve husbandry conditions. |
| Abstract: |
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| Database: |
Production |
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