Plasma free-corticosteroid concentrations, aggressive behaviour and levels of motivation to interact socially and explore a novel environment were observed to test the hypothesis that the chronic stress response previously observed in tether-housed pigs may have been due to unresolved aggression between adjacent pigs, and was attributable to the design of the stall. Twenty-five pregnant gilts were housed either in unmodified tether stalls; modified tether stalls (designed to reduce aggressive interactions between adjacent pigs by the addition of steel mesh to part of the stall division); cage stalls (also with mesh divisions); and a group pen for 7 pigs. Gilts in the unmodified tether stalls showed a sustained elevation of free-corticosteroid concentrations, indicative of a chronic stress response, changes in their level of motivation to interact with stimulus pigs in a standard test, and a higher proportion of aggressive interactions between neighbouring pigs resulting in withdrawal rather than retaliation. These results suggest reduced welfare in the unmodified tether stalls. The addition of mesh to the sides of the tether stalls reduced the number of interactions between neighbouring pigs compared to the unmodified tether stalls treatment and virtually eliminated aggressive interactions. Concomitant to the reduction in aggressive interactions was a reduction in free-corticosteroid concentrations, suggesting that the welfare of pigs in the modified tether stalls, cage stalls and group treatments was similar. It is concluded that modifying the design of the tether stall to minimize aggressive interactions between adjacent pigs improves welfare by avoiding a chronic increase in free-corticosteroid concentrations.
|Publication Title||Applied Animal Behaviour Science|
|Author Address||Anim. Res. Inst., Dep. Agric. Rural Affairs, Werribee, Vic. 3030, Australia.|
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