Occurrence: Worldwide, most prevalent where stalls still allowed.
Age affected: Sows.
Causes: Boredom in stalls/tether.
Effects: Repetitive behaviour (stereotypy).
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 showed that a large part of the behaviour was 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.
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. 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.
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.
Mode of transmission
Bar biting is not transmissible and only occurs in conditions where sows are confined in stalls or tethers on limited rations. Associated behaviours may occur in similar situations in other housing types.
The only physical sign that bar biting has occurred is excessive wear on the molars.
Treatment and prevention
The simple solution to bar biting and other stereotypical behaviour in stalls and tethers is to release the animals into loose housing. The EU ban on stalls and tethers has eliminated most stalls, but confinement at farrowing and after mating may still be practised and the behaviour can still be observed. Release 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.