The Evidence for a Causal Link Between Disease and Damaging Behavior in Pigs

Teagasc Researcher, Laura Boyle, and others, tell us more about the link between disease and damaging behavior in pigs.

Read the full article here: Boyle et al. 2022, Link disease damaging behaviour (PDF)

Background

Damaging behaviors (DB) such as tail and ear biting are prevalent in pig production and reduce welfare and performance. Anecdotal reports suggest that health challenges increase the risk of tail-biting. The prevalence of tail damage and health problems show high correlations across batches within and between farms. There are many common risk factors for tail-biting and health problems, notably respiratory, enteric and locomotory diseases. These include suboptimal thermal climate, hygiene, stocking density and feed quality. The prevalence of tail damage and health problems also show high correlations across batches within and between farms. However, limited evidence supports two likely causal mechanisms for a direct link between DB and health problems. The first is that generalized poor health (e.g., enzootic pneumonia) on farm poses an increased risk of pigs performing DB. Recent studies indicate a possible causal link between an experimental inflammation and an increase in DB, and suggest a link between cytokines and tail-biting. The negative effects of poor health on the ingestion and processing of nutrients means that immune-stimulated pigs may develop specific nutrient deficiencies, increasing DB. The second causal mechanism involves tail-biting causing poor health. Indirectly, pathogens enter the body via the tail lesion and once infected, systemic spread of infection may occur. This occurs mainly via the venous route targeting the lungs, and to a lesser extent via cerebrospinal fluid and the lymphatic system. In carcasses with tail lesions, there is an increase in lung lesions, abscessation, arthritis and osteomyelitis. There is also evidence for the direct spread of pathogens between biters and victims. In summary, the literature supports the association between poor health and DB, particularly tail-biting. However, there is insufficient evidence to confirm causality in either direction. Nevertheless, the limited evidence is compelling enough to suggest that improvements to management and housing to enhance pig health will reduce DB. In the same way, improvements to housing and management designed to address DB, are likely to result in benefits to pig health. While most of the available literature relates to tail-biting, we suggest that similar mechanisms are responsible for links between health and other DB.

Conclusions

Sharing of common risk factors and correlations between poor health and DB and sharing of risk factors is evidence of a clear link at individual and batch/farm level. Their circular relationship, with some evidence of two-way causal mechanisms, makes it difficult to understand the complex underlying mechanisms linking poor health to DB. Nevertheless, the undeniable links offer hope of simultaneous progress on two of the main challenges to the sustainability of pig production, namely, growing public concerns for pig welfare and the threat of antimicrobial resistance arising from mis/over use of antibiotics. The myriad of links between tail-biting, one of the major threats to pig welfare and poor health, the major cause of antimicrobial use, means that efforts to address non-infectious risks for certain diseases will simultaneously reduce the risk of DB and vice versa. At a practical level, the findings have two important implications for the renewed efforts to stop tail docking pigs in the EU. Firstly, the increased risk of tail-biting in long tailed pigs, at least in the interim, means there is an urgent need for protocols for antibiotic use in bitten pigs. Secondly, farmers need to focus on overcoming disease challenges, as well as on reducing common risk factors for disease and tail-biting if they are to raise undocked pigs successfully.

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