Towards a common conceptual framework and illustrative model for feather pecking in poultry and tail biting in pigs – 6. Disease framework

This is post 6. “Disease framework” of:

Towards a common conceptual framework and illustrative model for feather pecking in poultry and tail biting in pigs – Connecting science to solutions

Marc B.M. Bracke^a, T. Bas Rodenburg^b, Herman M. Vermeer^a, Thea G.C.M. van Niekerk^a
a Wageningen Livestock Research
^b Wageningen University, Dept. of behavioural ecology

Reading guide

This is one of 8 blog posts under the heading of: “Towards a common conceptual framework and illustrative model for feather pecking in poultry and tail biting in pigs – Connecting science to solutions”. It contains the following sections/posts:

1. Introduction, specifying the need to compare feather pecking (fp) in layers and tail biting (tb) in pigs
2. Terminology, specifying the various concepts involved in fp/tb.
3. Overview of main similarities and differences between feather pecking and tail biting
4. Farmer as a risk factor, emphasising, perhaps for the first time, that the farmer is a kind of ‘animal’ that is part of the problem (and the solution).
5. Models, reviewing available conceptual models of fp and tb, as well as presenting a new ‘face model’.
6. Disease framework, arguing that fp/tb may be regarded as a medical disorder, over and above being an abnormal behaviour per se.
7. Evolution and domestication, emphasising the need to view fp/tb as a phenomenon an evolutionary and genetic background.
8. References

The entire text (8 posts) can be downloaded as one pdf here.

6. Disease framework

Brunberg et al. (2016) characterise feather pecking (fp)/tail biting (tb) as an abnormal behaviour. However, they do not frame it as a disease. This section deals with the question whether fp/tb may/should be regarded as a disease, i.e. as a medical disorder, in particular a mental/behavioural pathology.

Of course, a lesion of the bitten/pecked animal (victim) can be regarded as a health disorder. However, when fp/tb is primarily seen as a behaviour of the actor, and not as a medical disorder, then adequately understanding the behaviour requires addressing the 4 why questions proposed by Tinbergen (1963). That is, a behaviour is sufficiently understood if we understand its mechanism/causation, its function/adaptation, its evolution/phylogeny (over generations) and its development/ontogeny (over the course of the individual’s life).

These aspects have been covered for the most part by Brunberg et al. (2016). However, aspects related to the importance and treatment of fp/tb were only marginally addressed.

When we were looking for a format to present the available information about fp at the www.henhub.eu/fp website, which was intended to inform farmers and the public, we decided to use the framework commonly used to describe medical disorders (Van Niekerk, 2015). This implies a characterisation of aspects like signs/symptoms/diagnosis (kinds of fp/tb), pathophysiology (mechanism), prevention, treatment and (economic) importance of fp.

Aspects related to (differential) diagnosis and pathophysiology may, for example, deal with the question whether ear biting, ear necrosis and flank biting are to be regarded as forms of (i.e. having a causation (and treatment) similar to) ‘tail biting. Conversely, Taylor et al. (2010) identified three types of tb in pigs: two-stage, sudden forceful and fanatic. These may be 3 different syndromes, all labelled ‘tb’.

The importance of the fp/tb problem does not only concern production losses and financial implications. It may also concern legal, psychological and ethical aspects such as animal integrity, the attitude regarding ‘blood’ in the pen, aversion to sustainability pressures among farmers, e.g. due to fear of (over-)regulation. As to the legal relevance, both tail docking and beak trimming have been banned in the EU some time ago, yet despite this farmers have mostly continued to perform these procedures routinely (and they were repeatedly being granted exemption to do so).

Once fp/tb is regarded as a problem that needs to be solved, the disease framework clearly has added value. For example, it is important to realise/understand that the management of risk factors applied for the purpose of prevention of fp/tb is not necessarily the same as applying them for the purpose of curative treatment, i.e. counteracting an outbreak of fp/tb. E.g. it is likely that more enrichment is needed to treat than to prevent fp/tb.

In the commercial practice of intensive livestock farming fp/tb are common problems, esp. when routine mutilations were no longer allowed. However, that does not imply that it is normal for the animals involved to show such abnormal behaviours. Fp/tb have been labelled so-called technopathies, i.e. pathological behaviours associated with agro-technologically designed living conditions. A common perception among applied ethologists, namely, is that there is a wide discrepancy between the animals’ living conditions in intensive livestock farming and the animals’ environment of evolutionary adaptation. That is, the living conditions are not normal. They are likely to overtax the animals’ control systems, thus leading to behavioural pathology/disorders. From an evolutionary perspective fp/tb is not part of the adaptive behaviours in which poultry/pigs deal with a variable environment. Instead these abnormal and injurious behaviours result from a frustrated need to perform rather species-specific foraging behaviours (scratching/rooting) for substantial periods of time, leading to boredom in relatively barren environments imposed under intensive livestock conditions.

The fact that these mutilating, harmful social behaviours (fp/tb) also (seem to) require preventive surgical interventions/mutilations (beak treatment, tail docking) strongly indicates that the label ‘medical disorder’ would seem to be appropriate. In humans self-harm and harmful social behaviour have been classified as (symptoms of) medical disorders, e.g. self-mutilation  in borderline patients and antisocial/dissocial personality disorder respectively. Preventive mutilation also implies an infringement of the animals’ integrity (a moral concern). It also indicates that the environment is not suited for the animals. Examples of preventive mutilations in human medicine are (religious) circumcision (e.g. for religious reasons or to prevent HIV in sub-Saharan Africa (Siegfried et al., 2009)), preventive mastectomy in women who are BRCA1 or BRCA2 mutation gene carriers (Zagouri et al., 2013), and prophylactic colectomy or even Whipple procedure (a major surgical operation involving the removal of the head of the pancreas, the duodenum, the proximal jejunum, gallbladder, and part of the stomach), e.g. in case of familial adenomatous polyposis (i.e. to prevent intestinal cancer). Whether in humans or animals, preventive surgery, even if intended to prevent ‘greater harm’ later in life, is not to be regarded as ‘normal’. E.g. in the case of pigs and laying hens the preventive mutilations have been associated with chronic ‘phantom’ pain because of neuroma formation (pigs: (Simonsen et al., 1991; Di Giminiani et al., 2017); poultry: (Gentle, 1986)). And, while the mutilation may solve the problem of future victims, in doing so it masks the problem (stress, mental pathology) that gives rise to neutrals becoming actors that engage in destructive, harmful social (or sometimes self-mutilating (van Zeeland et al., 2009)) behaviours. To paraphrase an early Dutch researcher of tail biting in pigs, Gerrit van Putten: the pig’s tail is a thermometer of animal welfare, which was discarded when the “temperature” became too high, i.e. the tails were docked rather than that housing conditions were improved. Also regarding the practice of preventing fp/tb using routine mutilations, it has been pointed out that these procedures are not fully effective. E.g. Zonderland et al. (2011) estimated a prevalence of 2.12% tail biting despite (very short) tail docking on Dutch farms.

Another indicator for viewing fp/tb as a medical disorder is the fact that fp/tb outbreaks lead to injuries (wounds), which may even escalate into cannibalism and/or death due to secondary infections of the wounds. This (progressive) loss of normal functioning and lack of homeostasis have typically been regarded as indicative of disease, esp. since these are also of economic significance to the farmers (Zonderland et al., 2011).

However, fp/tb is not just a problem because of wounds inflicted on the victims. As Brunberg et al. (2016) rightly point out, the (acute pain of the) victim is not the only welfare concern. An important part of the (more chronic) welfare problem concerns the stressors/behavioural deprivations that lead neutral animals to become actors of fp/tb. Fp/tb, therefore, is not just a medial disorder because of the clinical wounds (and surgical prevention practices), but also because of the likely mental disorder leading to the abnormal fp/tb behaviour shown by the actors. Taylor et al. (2010) distinguished three types of tail-biting pigs: two-stage (where tail biting is preceded by more gentle tail-in-mouth (TIM) behaviour), sudden forceful (without prior TIM, e.g. to get access to the feeder) and fanatic tb. The latter was also labelled as ‘obsessive’ and ‘persistent’, and may thus be classified tentatively as an ‘obsessive-compulsive’, which seems to come close to labelling this type of tb as an obsessive-compulsive mental disorder.

Formerly, harmful social behaviours like fp and tb have been labelled as ‘vices’. However, that label implies seeing the actors as a kind of criminals. In fact, and esp. the medical framework, would turn the actor into a kind of victim too, i.e. a victim of inappropriate/depriving/stressful living conditions of intensive farming.

A related point indicative of fp/tb being a medical disorder is the fact that fp/tb problems tend to spread in a pen (and perhaps also across pens). This may make fp/tb resemble an infectious disease/epidemic. In other words, fp/tb has disease-like properties: the behaviour has a tendency to escalate into a fp/tb outbreak. While it may be that novelty and reward (the taste of blood) may account for the frantic and ‘contagious’ appearance, the behaviour seems to be ‘contagious’, in that other animals in a pen/enclosure may acquire the behaviour once the first animal has started to engage in it. In this respect, it may be noted, that esp. in pigs often the pen is regarded as an ‘experimental unit’, while it remains to be shown that pigs in neighbouring pens remain unaffected by (the arousal caused by) ongoing tb.

A further disease-like property of fp/tb is the role of stress in the aetiology of the problem.  Many diseases are aggravated by common stressors like high stocking densities and limited access of food or a poor climate, e.g. because stress may reduce the immune response needed to combat the disease. Similar stressors also play a role in triggering fp/tb. However, the underlying pathophysiological mechanism may not be the same, as stimulation of the (humoral) immune response has been shown to predispose (rather than inhibit) fp in laying hens (Parmentier et al., 2009).

Finally, it may be pointed out that most major textbooks describing the diseases of poultry/laying hens and swine/pigs already have a chapter or section on fp and tb respectively. In that respect, a start has been made to recognise fp and tb as a medical/mental/behavioural pathology. The conclusion of this section, we believe, justifies a more proper recognition of fp/tb as a medical disorder, i.c. a mental disorder, in the future.

Reading guide

This was blog post nr. 6 under the heading of: “Towards a common conceptual framework and illustrative model for feather pecking in poultry and tail biting in pigs – Connecting science to solutions”. It contains the following sections/posts:

1. Introduction, specifying the need to compare feather pecking (fp) in layers and tail biting (tb) in pigs
2. Terminology, specifying the various concepts involved in fp/tb.
3. Overview of main similarities and differences between feather pecking and tail biting
4. Farmer as a risk factor, emphasising, perhaps for the first time, that the farmer is a kind of ‘animal’ that is part of the problem (and the solution).
5. Models, reviewing available conceptual models of fp and tb, as well as presenting a new ‘face model’.
6. Disease framework, arguing that fp/tb may be regarded as a medical disorder, over and above being an abnormal behaviour per se.
7. Evolution and domestication, emphasising the need to view fp/tb as a phenomenon an evolutionary and genetic background.
8. References

The entire text (8 posts) can be downloaded as one pdf here.

Acknowledgements

These blog posts have been made possible by the Hennovation project (HORIZON 2020 ISIB-02-2014 project, Grant no. 652638).