Occurrence: Worldwide Age affected: Sows
Photo: Elsevier International

Effects: Repetitive behaviour (stereotypy).

• Detailed causes
• Clinical signs
• Diagnosis
• Treatment and control

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Detailed causes

Bar biting is a behaviour pattern seen in sows confined in stalls or tether systems. It was considered a stereotypy ( a repeated, relatively invariant pattern of behaviour with no obvious function) for many years, but observations during nutritional experiments have shown that a large part of the behaviour is associated with food restriction. It appears that sows with food intakes restricted by volume express foraging behaviour in loose housing, and bite the bars of their stalls when stalled or tethered.

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Clinical signs

Sow 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 behaviour 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 behaviour pattern include bar sucking, chain chewing and excessive water drinking, and, in outdoor sows, stone chewing.

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Diagnosis

Bar biting and related stereotypical behaviour 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 behaviour is extensive foraging.

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Treatment and control

The simple solution to bar biting and other stereotypical behaviour 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 no 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.

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