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Tail biting and tail docking: Biology, welfare, economics

Tail biting is one of the main behaviour problems in pig production, causing reduced welfare and considerable economic losses when outbreaks occur. Even though substantial scientific and practical efforts have been made to solve the problem, the problem still persists. Research in northern Europe leads to a better understanding of the problem.

By Anna Valros, Linda Keeling, Adroaldo Zanella, Karen Thodberg and Jarkko Niemi

Most countries have decided to continue tail docking as a means to decrease this symptom of reduced welfare. Denmark is one of them – the other Nordic countries in Europe, however – Finland, Sweden and Norway have all decided to ban tail docking. The Nordic countries therefore make an interesting research area.

Hence, a group of Nordic researchers joined forces and approached the problem in an interdisciplinary project supported by the Nordic Joint Committee for Agricultural and Food Research. The main goal was to provide new scientific and practically applicable information on how to reduce the risk for tail biting, using both economically sound and animal-welfare-friendly measures. The project aimed at producing information on biological mechanisms behind tail biting; estimating welfare consequences of using tail docking as a preventive measure; and developing a model that estimates the effects of prevention of tail biting on the overall welfare and economic performance of pig production.

Individual and genetic differences
Even though risk factors for tail biting are well-documented, there is a big individual and between-farm variation in the occurrence of tail biting. One reason for this might be that there is an underlying, biological mechanism that increases the risk of becoming a tail biter, or a victim of tail biting. There are studies showing differences in tail biting prevalence between different pig breeds. Gender is also known to influence the risk of being tail bitten. Hence, there might be individual differences in the susceptibility to become a victim or a tail biter.

To study this further, the researchers selected pigs based on their observed behaviour. The pigs were either tail biters, victims of tail biting or neutral pigs (not biting, not bitten) from pens either with or without tail biting. The activity of the autonomic nervous system (ANS) of different tail biting phenotypes indicated that both victims and biters may have a dysfunctional autonomic regulation. Dysfunction of the ANS, which may indicate a degree of psychological disturbance, may thus be related to the development of tail biting. Victims had several signs of higher stress levels than all other groups, which can certainly be due to being bitten, but which may also be a reason for being bitten. Victims showed a general ‘sickness response’, various interrelated illnesses, and suppressed thyroid hormone T3. Biters also showed a slightly higher chronic stress level than controls, which further supports the hypothesis that stress might be a cause for the biting.

The results of studies on gene expression of the pigs described above showed that neutral pigs in tail biting pens appeared to differ in their gene expression most from the other phenotypes: 18 genes were differently expressed in these pigs compared to all other categories. These included genes with an effect on leanness in pigs, indicating that neutral pigs in tail biting pens are fatter compared to all other categories. They also included genes with an effect on social behaviour, indicating that these pigs are less pig-directed. Furthermore, genes with effects on novelty seeking and the brain transmitter dopamine differed. These differences are interesting considering our results regarding feeding (below) and the behavioural differences found between phenotypes. Despite not being involved in tail biting, neutral pigs in non-tail biting pens performed and received more pig-directed abnormal behaviours than neutral pigs in tail biting pens. The neutral pigs in tail biting pens were more directed towards pen fittings.

Reduced feed intake
The researchers did not find signs of disability to digest or absorb nutrition in tail biters, even though nutritional problems have been suggested as a reason for tail biting. On the other hand, their results show that neutral pigs in tail biting pens might have reduced feed intake. One might speculate that they stay non-bitten because of not moving to the feeders, which might be supported by the notion that over half of tail biting and third of the aggression was seen near the feeder in a trial where there was only one feeder per 10-12 finisher pigs.

In addition, the researchers found that pigs in tail biting pens differ from pigs in non-tail biting pens in regard to certain minerals, amino acids and jejunal morphology, which might be connected to elevated stress or reduced feed intake of tail biting pen pigs. They also found that tails are bitten more frequently in pigs which have a poor genetic average daily weight gain.

Plenty of evidence showed that tail biting is linked to the health status of the pigs, the association being two-way. Pigs suffering from other health disorders, leg disorders in particular, are more likely to have their tails bitten as compared to healthy pigs. On the other hand, tail bitten pigs are more likely to suffer from other health disorders when compared to non-tail bitten pigs, and tail damage and other health disorders are likely to occur within a short time period. Victims of tail biting had more severe inflammatory lesions than all other groups, especially in the respiratory organs, but it is not known if this is a cause of, or an effect of, being tail bitten. The risk of severe tail biting can be reduced by enriching the environment from birth. The research team found that providing additional material in farrowing pens resulted in less oral manipulation of other piglets, as compared to farrowing pens with an ordinary level of enrichment. The severity of tail biting during the growing period was significantly reduced in the pigs that had had additional enrichment before weaning, although the study did not show differences in the overall prevalence of tail biting. This supports earlier findings on the interaction between early enrichment and behavioural development in piglets.Tail docking is not an optimal solution to avoid tail biting. Earlier studies show that docking only limits the risk of biting, and only if a large part of the tail is removed, at least more than half of the tail. However, results from these projects show that removal of 50% or more of the tail leads to pain for at least six hours after docking, and the more the tail is docked, the more pain the piglets suffer. In addition, the more the tail is docked, the more neuromas form, indicating an increased risk for hyperalgesia, i.e. an increased sensitivity to pain, and spontaneous pain. Docking also influences the social behaviour of pigs later in life.

Prevention and immediate response
Economic consequences of tail biting and measures to prevent it depend on the prevalence and severity of tail biting on the farm. Tail biting resulted in substantial economic losses especially if the fattening of the pig could not be continued as planned. However, in most cases, veterinary treatments, extra labour and carcass condemnations were causing major losses.

Nordic on-farm datasets suggested that immediate response to tail biting by the caretaker is important to prevent further damage. Tail biting behaves like an epidemic: There is an elevated risk of further cases to occur in the pen, if there have already been one or more cases in the same pen. The researchers’ analysis suggests that it is economically profitable to put effort in preventing further cases from occurring, after the first case has been observed in the pen. Whether it also is economically profitable to invest in e.g. straw-based housing varies between farms. Moreover, preliminary results suggest that when choosing whether to allocate resources to more space or more enrichment – either enrichment as such or altering the housing type to allow e.g. straw bedding – the option of more enrichment would probably be economically more efficient.Several of the team’s results point towards an interesting finding: There may be factors protecting against tail biting in those pigs that remain unbitten despite being housed in pens with on-going tail biting problems. In addition, as the research group provides further and strong evidence that health and tail biting is linked, and as there seems to be a two-way interaction, this health-behaviour connection warrants further investigation.

Feeding is an important factor in tail biting, but since this does not seem to be attributable to digestive or absorption problems, the focus should be directed to feeding and foraging behaviour. The results further confirm the notion that enrichment is a very important part of reducing the problem of tail biting. It is important to use enrichment already during the nursing period, and enrichment appears to be an economically viable way of reducing the risk for tail biting on-farm.

Tail docking has been shown to only be efficient to reduce tail biting when such a large proportion of the tail is docked that the docking itself causes rather serious welfare problems. Research should therefore continue to focus on finding alternative preventive measures.


  • Tail biting and tail docking: Biology, welfare, economics

    Tail docking with a gas-powered docking device. Picture by Liat Romme Thomsen

  • Tail biting and tail docking: Biology, welfare, economics
  • Tail biting and tail docking: Biology, welfare, economics
  • Tail biting and tail docking: Biology, welfare, economics

    Anna Valros, professor of animal welfare, University of Helsinki, Finland

Anna Valros, Linda Keeling, Adroaldo Zanella, Karen Thodberg and Jarkko Niemi

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