Written by Maartje De Vos, Researcher Swine, Global R&D
Tail biting remains a significant welfare and economic challenge in modern swine production. Despite decades of research and the implementation of management strategies such as enrichment, stocking density adjustments, and tail docking, the issue persists across systems and regions.
A key reason for this persistence is its multifactorial nature. Tail biting results from interactions between environmental conditions, nutritional factors, health status, gender and genetics. Increasingly, research points to the importance of underlying physiological mechanisms in both the biter and the bitten pig.
Understanding these physiological processes is essential for the development of targeted nutritional strategies and feed additives that can improve resilience and reduce the occurrence of damaging behavior.
Tail biting as a stress-driven disorder
A consistent finding across studies is the involvement of the stress response system – particularly the hypothalamic–pituitary–adrenal (HPA) axis – in tail biting behavior. Both biters and victims show elevated cortisol levels (Rabhi et al., 2020), suggesting that tail biting is associated with a shared stress response rather than simple aggression.
Chronic activation of the HPA axis has multiple physiological and behavioral consequences. While short-term stress can enhance alertness, prolonged stress reduces the animal’s ability to cope with new environmental or management challenges (Valros et al. 2013). This is reflected in altered feeding behavior, reduced growth performance, and increased instability in social interactions.
Importantly, stress in this context acts both as a cause and a consequence. It can predispose pigs to initiate tail biting and can also intensify once biting occurs, creating a reinforcing cycle.
Neurotransmitter imbalance: the role of serotonin
Behavioral regulation in pigs is strongly influenced by neurotransmitters, particularly serotonin. This neurotransmitter is closely associated with emotional stability, impulse control, and social behavior.
Studies have shown that tail biters – and to a lesser extend victims – often show lower circulating serotonin levels, compared to unaffected pigs (Ursinus et al. 2014). Reduced serotonergic activity may impair behavioral control, increasing the likelihood of abnormal behaviors such as tail biting.
From a nutritional perspective, this is highly relevant. Serotonin is synthesized from the essential amino acid tryptophan. Dietary tryptophan availability influences serotonin synthesis in the brain. This creates a connection between diet composition and behavioral outcomes, positioning the serotonergic system as a potential target for nutritional intervention.
GABAergic system and anxiety regulation
In addition to serotonin, the gamma-aminobutyric acid (GABA) system plays a crucial role in behavior regulation (Phootha et al. 2022). GABA is the main inhibitory neurotransmitter in the central nervous system and is essential for controlling neuronal excitability.
Reduced GABA activity is associated with increased anxiety and a greater risk of aggressive or abnormal behaviors. When both serotonergic and GABAergic systems are dysregulated, pigs are less able to regulate stress and control behavior, creating conditions in which tail biting is more likely to occur.
Inflammation as a central component
Tail biting is not only a behavioral issue but also a physiological condition involving inflammation. In bitten pigs, tissue damage can lead to activation of the innate immune system (Heinonen et al. 2010), leading to elevated inflammatory markers, increased body temperature, and reduced feed intake. Furthermore, the compromised tissue integrity increases the risk of secondary infections, further impacting health and performance.
At the same time, research indicates that tail biters themselves may also experience underlying inflammatory conditions, particularly in the gastrointestinal tract, such as gastric irritation or ulcers (Czycholl et al 2023). This suggests that tail biting behavior may be a manifestation of internal discomfort rather than simply unwanted behavior.
The role of the microbiota-gut-brain axis
The role of nutrition in tail biting is increasingly being understood through the concept of the microbiota-gut-brain axis. Diet directly shapes the gut microbiota, influencing its diversity and metabolic activity.
Nutritional factors such as imbalanced protein levels, insufficient tryptophan, low fiber intake, abrupt dietary changes, or antibiotic use can disrupt microbial homeostasis (Kobek-Kjeldager et al. 2022). These changes can alter the production of metabolites that influence brain function and behavior.
This reinforces the idea that tail biting should not be viewed solely as a behavioral disorder but as a multifactorial condition in which gut health plays an important role.
From physiology to product design
The physiological complexity of tail biting highlights the need for multi-target approaches. Tail biting is associated with alterations in neurobiology, stress physiology, and metabolic status, including changes in serotonergic activity and dysregulation of the hypothalamic–pituitary–adrenal (HPA) axis. These findings support the development of strategies that simultaneously target multiple biological pathways.
Today, more integrated approaches are being developed, combining multiple modes of action within a single product. In particular, plant-derived bioactive compounds represent a promising class of functional ingredients, as they have been shown to influence physiological processes relevant to behavior and resilience.
Zentail is designed to deliver anxiolytic-like, anti-inflammatory and stress-mitigating effects, reducing behavioral escalation, and contributing to improved group stability. By targeting both the biter and the bitten pig, this product contributes to an overall increase in resilience within the population. A key practical advantage is its flexibility, as the product is designed independently of diet formulation, allowing easy integration into existing feeding programs.
Conclusion
Tail biting should no longer be treated as an isolated behavioral issue, but rather as a complex physiological syndrome involving stress regulation, neurobiology, inflammation, and gut health.
Both biters and bitten pigs are affected by underlying imbalances that reduce their ability to cope with environmental challenges. Understanding the roles of neurotransmitters such as serotonin and GABA, the stress hormones, and inflammation and the microbiota-gut-brain axis have opened the door to more targeted interventions.
By translating physiological insights into practical nutritional solutions, the industry can both improve animal welfare and enhance performance, while reducing reliance on invasive management practices, like tail docking. Products such as Zentail illustrate how these physiological principles can be applied in practice to support resilience and reduce tail biting at farm level.