Agonistic Interactions between Littermates Reappear after Mixing Multiple Litters at Weaning in Pigs

Maja Prevolnik Povše,Dejan Škorjanc,Janko Skok,Nikolina Mesarec

doi:10.3390/agriculture11090844

Abstract

Weaning involves mixing of unfamiliar litters and is accompanied by an outbreak of aggression, which is usually attributed to between-litter (BL) interactions. In the present study, we thus focused on post-weaning agonism (fighting and mounting) between littermates (within-litter, WL). Two litters were weaned into two pens separated by an empty pen and connected by narrow passages that were opened 24 h after weaning. WL interactions accounted for 38% and 68% of all fights and mounts, respectively, during a 7-day experimental period. After the passages were opened, not only BL, but also WL interactions increased significantly (by 6- to 7-fold on the first day of mixing). WL fights then gradually decreased, while WL mounts continued to increase. During the experimental period, the proportion of both WL fights and mounts decreased. The majority of WL fights (≈80%) and mounts (≈65%) occurred in home pens. A significantly higher percentage of draws was found in WL fights (50% of initiator wins and 41% of draws) compared to BL fights (80% of initiator wins and 11% of draws). Results also showed less asymmetry in the body weight of piglets involved in WL interactions. Mixing of litters at weaning was shown to involve not only intense interactions between unfamiliar piglets but also the recurrence of agonistic interactions between littermates, which is something we should keep in mind when pursuing the highest standards of weaner welfare.

Highlights

Weaning, as is commonly carried out in contemporary intensive pig production, is known to trigger an outburst of aggression
Contrary to the interactions between piglets from different litters, where fighting predominated over mounting (3.5:1 ratio), there was an almost perfect balance (1:1) between both interactions when the confronted piglets were from the same litter
We confirmed that within-litter interactions, both fighting and mounting, increased significantly during the first two days after litters were spontaneously combined into a single weaning group and gradually decreased thereafter

Summary

Introduction

As is commonly carried out in contemporary intensive pig production, is known to trigger an outburst of aggression In this process, two or more unfamiliar litters are brought together in a new weaning pen, which causes nutritional, psychosocial, and environmental changes associated with production practices, such as diet change, separation from the mother, mixing of non-littermate piglets, relocation/transportation, and/or changed temperature and air quality parameters [1,2]. In addition to interactions between unfamiliar individuals, the changes related to weaning most likely break down the previously established dominance hierarchy within the litter and stimulate new interactions related to dominance position among littermates. From an animal welfare perspective, it is important to obtain information on the possible changes in the dynamics of interactions between littermates that result from mixing unfamiliar litters

Methods

Results

Discussion

Conclusion