What is tail-biting in pigs?
Tail biting is one of the most critical problems in pig farming, occurring in both conventional and alternative production systems. The term refers not only to biting but also to suckling and chewing or simply putting the other pig's tail in the mouth (often called "tail-in-mouth behavior"). When bitten, the victim pig might react by vocalizing or escaping. Tail biting usually causes damage, ranging from mild bite marks to the tail being partially or fully removed, as seen in the pictures below.
The Impact of Tail-Biting on Pig Welfare and Farm Economics
Tail biting is very painful and stressful for the victim pigs. When it occurs repeatedly, as is often the case, tail biting leads to chronic discomfort and stress, resulting in a great decline in their welfare. This may alter the animal's normal activities. For example, in many cases, victim pigs eat less. In addition, tail biting is related to reduced health, with several studies indicating that wounds from tail biting can facilitate inflammations of the internal organs. All these complications seriously impact farm economics: within the European Union, the costs of tail-biting wounds are calculated to be around €2.0 per finisher pig.
What causes tail biting in pigs?
Unfortunately, the exact cause of tail biting remains unknown. However, it is probably linked to increased stress levels induced by numerous risk factors, both internal (e.g., breed, sex) and external (e.g., floor type, air quality). These risk factors interact, so it is incredibly challenging to study them. Therefore, there is much uncertainty regarding the risk factors of tail biting, making it harder to deal with this problem.
Environmental Factors Contributing to Tail-Biting
The pigs' environment may be the most crucial factor for triggering tail biting. For example, studies have shown that the risk of tail biting increases when pigs do not have enough feeding space. Thermal discomfort (too hot, cold, or humid) and air draughts can lead to tail-biting. The space allowance per pig is also a highly important risk factor for tail biting. In a study in Finland, tail biting prevalence decreased when space allowance increased from 0.7 m2 to 1.5 m2 per finishing pig. For comparison, the minimum space allowance per finishing pig in the European Union (Council Directive 2008/120/EC) is 0.65 m2 for pigs weighing between 85 kg and 110 kg and 1.00 m2 for pigs over 110 kg. Space restriction can cause irritability, e.g., because there is not enough lying space. On the other hand, increased space allowance is beneficial as it can help an individual pig avoid a tail-biting pen mate.
However, the pigs' environment is not only limited to the basic needs of eating, drinking, and lying. Pigs are curious and intelligent animals, meaning that a bare environment, like the one provided for them on conventional farms, is not appealing enough. A typical concrete pen with a few feeders and drinkers and a slatted part for elimination (defecation and urination) makes the pigs bored, stressed, and irritable, thus leading them to tail-biting performance. Furthermore, in nature, pigs spend much of their time foraging for food by rooting the surface of the ground. In a conventional farm, feed is, of course, provided by humans in a way that is easy for all pigs to access. The pigs are strongly motivated to forage around even if they are satiated. Still, in the aforementioned example of a pen, there is no chance of discovering a nice cluster of mushrooms or a couple of earthworms. Therefore, their strong natural motivation to explore and root will be redirected to the other pigs.
The Role of Diet in Tail-Biting Behavior
In addition, many researchers have highlighted the effect of diet on tail biting as well. The nutrient that has received the most attention is protein. In certain studies, pigs fed diets with lower protein content were more performed more foraging behavior and/or tail biting than pigs fed balanced diets. As explained before, increased foraging behavior can lead to tail biting if it is not satisfied. Another explanation is that a diet low in protein is probably deficient in the amino acid tryptophan. Tryptophan is a precursor for synthesizing serotonin, a neurotransmitter associated with positive moods and emotions. Importantly, tryptophan is an essential amino acid, meaning that pigs cannot synthesize it on their own but have to obtain it through their food. Therefore, if a pig consumes a diet deficient in tryptophan, then the levels of serotonin would decrease, thus bringing the pig into a negative mood.
Sickness as a Potential Cause of Tail-Biting
In recent years, sickness has also been suspected as a contributing factor to tail biting. The theory is that upon activation of the immune system, the body redistributes the available amino acids to immunity-related processes. As a result, there might be a lack of amino acids for other processes. For example, tryptophan might be used up for cytokine production, therefore reducing the levels of serotonin, similar to what was explained in the previous paragraph.
How Can Farmers Prevent and Manage Tail-Biting?
Admittedly, avoiding tail-biting altogether is extremely difficult to achieve. Nevertheless, the first thing a farmer should do is make sure the basic needs of his herd are met. Competition for feeding, water, and space should be avoided or minimized. It is suggested that feed be provided in a way that all pigs can access simultaneously (see the picture below). Regarding water, it is recommended to have one nipple per 12 pigs. Both feed and water should be of excellent quality. The floor of the pen should be clean and dry because poor hygiene can cause sickness or asymptomatic diseases. Temperature and air quality should be checked regularly.
Besides these, the farmer should try to make the environment as appealing to the pigs as possible. Straw is an excellent enrichment material and is efficient even in low amounts. Other objects often used in commercial farms include wood shavings, jute bags, ropes, fresh or processed wood pieces, plastic toys, and metal chains. In general, pigs prefer deformable, destructible, and ingestible materials. Hence, plastic toys and chains are the least recommended ones.
Tail docking should be considered only as a last resort. Studies have shown that tail docking can indeed reduce tail biting. However, it does not solve the root of the problem. Therefore, pigs with dock tails reared in a barren environment might not bite their pen mates’ tails but will focus on other body parts (ears, legs, etc). It should be noted that in the European Union, routine tail docking is banned.
References
Averós, X., Brossard, L., Dourmad, J., De Greef, K. H., Edge, H. L., Edwards, S. A., & Meunier-Salaün, M. (2010). A meta-analysis of the combined effect of housing and environmental enrichment characteristics on the behavior and performance of pigs. Applied Animal Behaviour Science, 127(3–4), 73–85. https://doi.org/10.1016/j.applanim.2010.09.010
Boyle, L. A., Edwards, S. A., Bolhuis, J. E., Pol, F., Šemrov, M. Z., Schütze, S., Nordgreen, J., Bozakova, N., Sossidou, E. N., & Valros, A. (2022). The evidence for a causal link between disease and damaging behavior in pigs. Frontiers in Veterinary Science, 8. https://doi.org/10.3389/fvets.2021.771682
Bus, J. D., Walderveen, A. van, Bolhuis, J. E., Boumans, I. J. M. M., & Bokkers, E. A. M. (2023). Protocol for Health Observations in Growing-Finishing Pigs (V1 ed.). DANS Data Station Physical and Technical Sciences. https://doi.org/doi/10.17026/dans-xt2-xpej
Meunier-Salaün, M. C., Monnier, M., Colléaux, Y., Sève, B., & Henry, Y. (1991). Impact of dietary tryptophan and behavioral type on behavior, plasma cortisol, and brain metabolites of young pigs1. Journal of Animal Science, 69(9), 3689–3698. https://doi.org/10.2527/1991.6993689x
Minussi, I., Gerrits, W. J. J., Jansman, A. J. M., Gerritsen, R., Lambert, W., Zonderland, J. J., & Bolhuis, J. E. (2023). Amino acid supplementation counteracts the negative effects of low protein diets on tail biting in pigs more than extra environmental enrichment. Scientific Reports, 13(1). https://doi.org/10.1038/s41598-023-45704-0
Munsterhjelm, C., Heinonen, M., & Valros, A. (2015). Application of the Welfare Quality®animal welfare assessment system in Finnish pig production, part II: Associations between animal-based and environmental welfare measures. Animal Welfare, 24(2), 161–172. https://doi.org/10.7120/09627286.24.2.161
Scientific Opinion concerning a Multifactorial approach on the use of animal and non‐animal‐based measures to assess the welfare of pigs. (2014). EFSA Journal, 12(5). https://doi.org/10.2903/j.efsa.2014.3702
Taylor, N. R., Main, D. C., Mendl, M., & Edwards, S. A. (2009). Tail-biting: A new perspective. The Veterinary Journal, 186(2), 137–147. https://doi.org/10.1016/j.tvjl.2009.08.028
Valros, A. (2023). Managing tail biting in pigs: Preventing risk factors or docking tails? In Elsevier eBooks (pp. 261–287). https://doi.org/10.1016/b978-0-323-85676-8.00002-x
Further reading
Optimizing Nutrition to Prevent Post-Weaning Diarrhoea in Piglets
Azolla: A Sustainable and Cost-Effective Protein Source for Pig Feed
Swine Biosecurity: Essential Practices for Disease Prevention and Herd Health
Pigs Health, Diseases & Symptoms
Tropical vs. temperate forages: Nutritional composition and fiber digestibility
Animal Welfare Standards: A Farmer's Guide to Balancing Ethical Practices & Market Access
Heat Stress in Dairy Cows: A Growing Concern
Livestock Welfare: Key Principles, Ethical Practices, and Strategies for Sustainable Farming