Bar biting is a behavior pattern seen in sows confined in stalls or tether systems. It was considered a stereotypy (a repeated relatively invariant pattern of behavior with no obvious function) for many years but observations during nutritional experiments have shown that a large part of the behavior is associated with food restriction. It appears that sows with food intakes restricted by volume express foraging behavior in loose housing and bite the bars of their stalls when stalled or tethered.
Sows penned or tethered in stalls with rails in front of them open their mouths wide and grasp the rail at head height. They then move their heads from side to side with the rail pressed as far back as possible. In the course of this movement, they generate large amounts of frothy saliva and grunt and squeal. This behavior pattern may continue for some hours ceasing when the sow is asleep or being fed and for a short while afterwards. There are few physical signs that bar biting has taken place. Other elements of this repetitive behavior pattern include bar sucking, chain chewing and excessive water drinking and in outdoor sows, stone chewing.
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Bar biting and related stereotypical behavior can be identified by inspection. To confirm its occurrence in a group of stalled or tethered sows it is necessary to be present for a period between the post-feeding period of quiet and the next feed. In loose sows the equivalent behavior is extensive foraging.
Treatment and control
The simple solution to bar biting and other stereotypical behavior in stalls and tethers is to release the animals into loose housing. This does not, however, address the underlying problem of feed-volume restriction via the diet. One treatment option may be to house the sows on straw. This reduces the problem but may not eliminate it. Alternatively, highly palatable and bulky feeds with relatively low nutrient density for example soaked sugar beet pulp may be added to the sows' rations.