Causes and consequences of tail biting in pigs: how to avoid it?

Tail biting, which has a multifactorial origin, represents both a major animal welfare and economic problem for the pig industry with losses due to reduced weight gain, increased on-farm veterinary treatment, culling, and carcass condemnation. The amount of research concerning tail biting has increased over the past two decades, particularly in the European Union (Henry et al., 2021).

Types of tail biting

Temple et al. (2014) and Prunier et al. (2020) talked about different types of biting that can be identified:

1. "Sudden-forceful” biting: it is common in the context of hierarchy formation and occurs mostly in the first hours after creating a new social group. It is more commonly seen when pigs are unable to access a desired resource such as food. This pattern follows a similar description to vulva biting in sows and anus biting and may be considered as an aggressive act due to frustration.
2. “Obsessive” biting: it occurs mainly, though not exclusively, in barren environments where pigs are likely to be thwarted in their need to perform exploration, object play or foraging behaviors. Obsessive tail biters spend much more time biting tails than other tail biting animals. This abnormal behavior might be comparable to stereotypies.
3. “Two-stage” biting: largely results from the inability of pigs to express natural behavior to root, chew and forage. It refers to a redirected exploratory behavior.

Risk factors

There are several main risk factors for tail biting (Temple et al., 2014; Boyle et al., 2022):

• Lack of enrichment material (eg: lack of straw) and barren floors in intensive farming systems.
• Poor ventilation: the excessive presence of certain gases (e.g.: ammonia), humidity and dust may act as stressors leading to increased discomfort. If this occurs under long-term conditions, it causes chronic stress.
• Thermal stress: due to large daily temperature fluctuations.
• High stocking density, large herd, and mixing of animals.
• Gastrointestinal discomfort: gastric ulcers increase the motivation of pigs to chew and the risk of tail biting.
• Poor health status. By one side, chronic pain is an important cause of discomfort and stress. And by the other side, ill pigs possibly show decreased reactivity to avoid tail biting.
• Suboptimal or imbalanced diet: imbalances in the amino acid composition of the diet, and both deficits and excesses of protein may trigger tail biting. Finally, lack of salt in the diet and low levels of tryptophan in the diet increase the pig’s’preference for blood and therefore affect the development of outbreaks.
• Individual factors (age, genetic).

Health and economic consequences of tail biting

Directly, tail biting causes more or less severe skin lesions, or amputation of part of the tail in post-weaning and fattening pigs (Prunier et al.,2020).

Indirectly, biting behavior can result in:

• Injuries such as lameness due to slipping during fights.
• Infections due to wounds caused by biting.
• Immunosuppression.
• Reduced growth.
• And, in some extreme cases, death.

Pathogens enter the body via the tail lesion and once infected, systemic spread of infection may occur. There is also evidence for the direct spread of pathogens between biters and victims (Boyle et al., 2022).

So, to avoid that local injuries get complicated and result in systemic infections, proper cleaning and disinfection of bites is required. Application of topical sprays containing antibiotics such as chlortetracycline may be recommended. If the infection spreads anyway, a systemic antibiotic treatment is then advised.

According to Niemi et al. (2021), tail biting lesions cost:

• £3.51 million per year to the UK pig industry.
• About €2,400 per year for a typical finishing herd in the Netherlands, (less than 1% of the sale value of the pigs, assuming 2% of pigs suffer from the lesions).
• €18.96 per victim of tail biting in Danish conditions (∼15% of the sale value of a pig with lesions).
• €1.1 reduction of the mean annual farm profit per produced pig (−15.1%) in Irish farms with a high prevalence of severe tail lesions reported.
• Around €2 (±€1.4) per finished pig (1–3% of the sale value of a pig) across Europe.

Prevention of tail biting

The prevention of tail biting is important for profitability and animal welfare.

Niemi et al. (2021) made a cost-effectiveness analysis of different measures to reduce tail biting lesions in fattening pigs. They analyzed the following measures: straw provision, improvements in ventilation, genetic changes, increased space allowance by 0.2 meters, provision of point-source enrichment objects, improvement in herd health and early warning systems.

They concluded that measures which were considered most efficient in reducing the risk of tail biting lesions are different according to the level of risk of tail biting:

• High risk of tail biting: straw provision can be cost-effective in preventing tail biting.
• Low risk of tail biting: the provision of point-source enrichment objects and other less costly but relatively effective measures can play an important role.

Talking about causes and prevention, Prunier et al. (2020) concluded that regarding:

• Aggressive biting: undernutrition of the fetuses due to reduced nutrient supply, cross-fostering and socialization early in life reduces its later occurrence. The practical consequence is that any means to allow piglets from different litters to interact from the second week of age should be encouraged.
• Non-aggressive biting: fetal undernutrition due to reduced nutrient supply, social stress due to competition and cross-fostering stimulate its occurrence later in life.
• Both types of biting: the use of familiar odors may contribute to their reduction when pigs are moved from one stage of production to another, by alleviating the level of stress associated with novelty of the environment.

In the case of enrichment materials, Temple et al. (2014) recommend that rooting material should be clean and renewed frequently due to pigs quickly lose interest in all novel objects regardless of their physical properties.

Removing the biter of the victim is an option (Chou et al., 2019). The use of sedative products such as azaperone for animals with aggressive behavior after group mixtures can be useful for tail biting prevention and/or in batches where a tail aggressive biting outbreak has started.

In that case, always taking into account that its suppression period is 18 days, we recommend following these indications when applying azaperone to maximize its effectiveness in the moments of regrouping pigs from the beginning to the fattening period:

• Dose = 1 ml/20 kg.
• Administer intramuscularly at the time of mixing the animals since its effect is rapid (5-10 minutes after injection).
• It has a sedative effect that lasts between 1 and 3 hours, however it is not usual that aggressive behaviors occur again.

In the next article, which will be published at the end of July, we will talk much more about the use of azaperone in order to prevent the consequences of hierarchical problems in pigs and sows.

Conclusions

Tail biting represents a major challenge for the pig sector and its prevention should focus on the provision of adequate rooting material and avoiding any situation that causes competition, frustration and stress.

Proper care of tail bites, applying topical antibiotic sprays when necessary, is important to reduce the risk of systemic infections.

References

• Boyle LA, Edwards SA, Bolhuis JE, et al. The Evidence for a Causal Link Between Disease and Damaging Behavior in Pigs. Front. Vet. Sci. (2022) 8:771682. doi: 10.3389/fvets.2021.771682.
• Chou JY, O’Driscoll K, D’Eath RB, et al. Multi-Step Tail Biting Outbreak Intervention Protocols for Pigs Housed on Slatted Floors. Animals (2019), 9, 582; doi: 10.3390/ani9080582.
• Henry M, Jansen H, Amezcua MdR, et al. Tail-Biting in Pigs: A Scoping Review. Animals (2021), 11, 2002. doi: 10.3390/ani11072002.
• Niemi JK, Edwards SA, Papanastasiou DK, et al. Cost-Effectiveness Analysis of Seven Measures to Reduce Tail Biting Lesions in Fattening Pigs. Front. Vet. Sci. (2021) 8:682330. doi: 10.3389/fvets.2021.682330.
• Prunier A, Averos X, Dimitrov I, et al. Review: Early life predisposing factors for biting in pigs. Animal (2020), 14:3, pp 570–587. doi: 10.1017/S1751731119001940.
• Temple D, Mainau E, Manteca X. Tail biting in pigs. The Farm Animal Welfare Fact Sheet, nº 8, (February 2014). FAWEC.