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Aggressive Behaviour in Pigs

Tail biting has always been a problem for pig farmers, often occurring unpredictably, and quickly causing severe damage.

Researchers have linked many nutritional factors to tail biting, including low dietary fibre, poor quality protein and deficiencies in iron, copper, salt, calcium, phosphorus or iodine. One research study showed that removing only salt from the diet increased tail biting, whereas removing all other supplementary minerals and trace elements did not. Therefore, it was suggested that general chewing behaviour, seen in all pigs, escalated into tail biting when a wound was made and the specific appetite for blood activated. This would be much more severe in protein or salt deficient pigs. The consequence of this theory is that anything which increases the general level of activity and exploratory chewing will increase the probability of tail biting.

Many environmental factors which make pigs more restless, such as hunger, extreme temperature or draughts, can also precipitate tail biting under commercial conditions. Nutritional factors may also have a similar effect, even when pigs are fed ad libitum.

It is known that pigs can recognise specific nutrient deficits in the diet. When given a dietary choice, they can select a mix of protein content, which is influenced by their genotype, age and previous nutritional history. Growing pigs are normally provided with a single diet for all animals over extended time periods of the growing/finishing phase. This means that the exact needs of each individual in each week are seldom matched by their diet.

It has been shown that growing pigs offered a diet deficient in protein increase foraging and exploratory behaviour, and that an amino acid imbalance can have the same effect.

In a relatively barren environment, exploratory behaviour is directed mainly to other pigs, with more massaging and chewing of pen mates. Such behaviour can increase the probability that tail biting will start.

Providing deep straw beds to enhance pig welfare may do little to prevent aggressive behaviour in growing animals compared to offering a small quantity of straw each day. Research carried out by ADAS suggests that straw provides comfort, acts as a foraging or exploratory substitute and can gut fill. UK legislation states that all pigs must have access to straw or other material to satisfy their behavioural needs.

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