However, tail docking is still common practice in many European countries, although several, including Finland and Lithuania have stopped routine tail docking altogether. However, many piglets in Europe are still routinely exposed to the cutting or cauterising of a part of the tail up to a week after birth, to prevent tail biting in their later life. This procedure is mostly done by the farmer during the first week of the piglets’ life without any pain relief.

Welfare issues
Tail docking has been found to be effective in reducing tail biting only when a considerable amount of the tail is docked. However, docking itself may create significant regulatory and health related welfare issues. The farm veterinarian has an important role in doing a farm-specific risk assessment and advising the farmer with preventive measures in case of tail biting outbreaks.

Economic losses due to tail biting
Various studies have reported that tail biting effects 2-12% of farms, costing the UK pig industry £3.51 million per year. In the Netherlands, a typical finishing herd spends about €2,400 per year tending to tail biting lesions (<1% of the sale value of the pigs while assuming 2% suffer from lesions) while Denmark spends €18.96 per tail biting victim (about 15% of sale value of a pig with lesions). Recently, a €1.10 reduction of the mean annual farm profit per pig produced (−15.1%) in Irish farms with a high prevalence of severe tail lesions was reported. Some authors suggest that the cost of tail-biting lesions across Europe is around €2.00 (±€1.4) per finished pig (1–3% of the sale value of a pig).

Risks factors
While there is no single cause as to why tail biting occurs, there is extensive literature identifying different potential causes, risk factors, and numerous trials investigating different solutions. Generally, tail biting is seen as an abnormal behaviour expressed under barren conditions resulting from the inability to fulfil the natural need for rooting, foraging, and exploratory behaviours. In addition, domestic pigs are exposed to many stressful challenges throughout their lives, and several of these have been identified as risk factors for the development of tail biting. These factors can be environmental, such as temperature, feeding method, lack of appropriate enrichment, and inappropriate pen design e.g., fully slatted floors. Several social factors like insufficient space at the feeder that leads to competition, high stocking density are important risk factors for tail biting, as are individual factors such as nutritional status and neurobiology. However, it is currently not fully understood how all these different and numerous factors contribute to the occurrence of tail biting.

Links with the gut microbiota
One factor that could provide the link between food-related behaviours, different types of stressors, and tail biting; is the gut microbiota. The gut microbiota plays a major role in regulating homeostatic processes in the host. Immunity, cardiovascular health, and digestive systems are impacted as well as certain metabolic processes. Major brain processes are also influenced by microbiota functions, linking the gut to the brain which is more commonly known as the microbiota-gut-brain axis.

One of the pathways between the gut and the brain is through the production of microbial metabolites containing neuroactive properties. Short-chain fatty acids (SCFA) are the main metabolites produced in the large intestine by anaerobic bacterial fermentation of dietary fibre. Acetate, propionate, and butyrate are the main SCFA plasma in the colon and are key components in gut-brain communication through signalling pathways.

Recent trials
The aim of a recent study published in 20211 was to determine whether matched sets of pigs that are biters, victims of tail biting, or controls (pigs not involved in a tail-biting episode), have a different microbiota composition, diversity, and SCFA plasma profile. Differences were expected between the biter versus the victim pigs when compared to the control pigs, given the stress of being involved in tail biting, differences between biters and victims might support the hypothesis that an unbalanced gut-microbiota and an altered SCFA profile play a role in the development of tail biting.

In this trial, scientists found reduced concentrations of SCFA plasma in the faeces of biter pigs as well as reduced SCFA plasma concentrations in the victim pigs. This study provided further evidence for the role of the gut microbiota composition, diversity, and for the specific role SCFA has in tail biting in pigs.

Conclusion
Future studies are required to confirm these changes and understand the potential causalities and interactions involved with tail biting.

Sources
The gut microbiota and microbial metabolites are associated with tail biting in pigs Scientific Reports volume 11, Article number: 20547 (2021).