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Towards a common conceptual framework and illustrative model for feather pecking in poultry and tail biting in pigs – 5. Models

This is post 5 on “Models” 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:

Introduction, specifying the need to compare feather pecking (fp) in layers and tail biting (tb) in pigs
Terminology, specifying the various concepts involved in fp/tb.
Overview of main similarities and differences between feather pecking and tail biting
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).
Models, reviewing available conceptual models of fp and tb, as well as presenting a new ‘face model’.
Disease framework, arguing that fp/tb may be regarded as a medical disorder, over and above being an abnormal behaviour per se.
Evolution and domestication, emphasising the need to view fp/tb as a phenomenon an evolutionary and genetic background.
References

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

5. Models

Table 3 shows a list of various models/figures that have been proposed to clarify feather pecking (fp)/tail biting (tb), including the recent model proposed by Brunberg et al. (2016). Our focus here was to compare models, esp. models originating from Wageningen University Research, in search for potential improvements. Not all models have been included in Table 3. For example, Valros and Heinonen (2015) propose a modified bucket model where the bucket is filled with acute and/or chronic stressors (cf also Valros (2017)).

Some model illustrations.

Since copy-rights are a problem for representing models, below a selection is given of models for which Wageningen UR (already) has the copy-rights. Other models can be obtained via the cited references or the internet. E.g. an example of the psychohydraulic model (Lorenz, 1950; 1978) can be found here.

Figure 7.3 below shows the tail biting (tb) model by Zonderland (2010a) (Fig. 7.3, p. 138).

The conceptual framework for tb originating from Bracke (2008) (reprinted in (Bracke, 2017)) is shown in Figure 1 below. This model was designed to construct the RICHPIG model (decision support system) to assess/calculate the welfare value of enrichment materials for pigs.

Figure 1. Schematic representation of the conceptual framework for assessing environmental enrichment for pigs. EMat: Enrichment material; AMI: animal-material interactions; I: Istwert, the environment as perceived by the animal; S: Sollwert, set point or norm (modified homeostatic model after Wiepkema (1987) and (Anonymous, 2001)). (Figure from Bracke (2008), permission granted by UFAW) (reprinted from (Bracke, 2017)).

Citation from Bracke (2017) relating the model to the principle of communicating vessels:

“Progressive feedback loops in the framework indicate that the animal’s welfare is good when proper enrichment satisfies the pigs’ need to explore and forage. When the enrichment is deficient, the animals will redirect their attention and show pen- and pen-mate directed behaviour. Note that this may imply a mechanism resembling the principle of communicating vessels (connected containers filled with liquid; see Wikipedia (2016c)). In accordance with this principle pigs may distribute their (motivation for) exploratory behaviour (the liquid) depending on the quality of the manipulable ‘materials’ available to them (cf Bracke et al. (2012)). Eventually, an outbreak of tail biting may occur, potentially evoking a positive feedback loop (an escalating outbreak) leading to cannibalism when no ‘proper enrichment’ is provided buffering and/or eliminating the (primary) cause/stressor.” (End of citation).

In the communicating-vessels model, for which we found some empirical evidence in pigs (Bracke, 2017), vessel size may change due to animal-properties like genetics; but also e.g. enrichment-based and other risk factors.

In the case of fp in poultry, in a classic paper Newberry et al. (2007) questioned the assumption of communicating vessels underlying the hypothesis that fp is redirected foraging behaviour as proposed earlier by Blokhuis (1986). Newberry et al. (2007) showed that birds with high levels of ground pecking as chicks were more likely to develop high levels of fp as adults compared to low ground pecking chicks. However, the high ground pecking chicks also continued to show high levels of ground pecking as adults, shedding doubt on the theory that fp would replace ground pecking.

Under ‘mechanism’ Van Niekerk (2015) presents both a balance model and a tipping-bucket model for fp (see also Van Niekerk (In prep.)). The bucket model was modified from a tb model originally proposed by Vermeer in Bracke et al. (2012). The main problem of the tipping-bucket model is that it suggests that fp/tb cannot stop, cannot be made undone (or perhaps only via an external ‘force’, e.g. a farmer taking adequate measures to correct the problem). Perhaps the model could be improved, e.g. by making a tumbler-type tipping bucket, such that it can be emptied, and then may restore its original position. However, this revised tumbler model would still be deficient in that post fp/tb set points are not the same as before (as a tumbler would suggest). Another option might be a series of buckets. Once tipped, the next bucket could stay down, with the next bucket being smaller, such that the next tipping point would be reached sooner, with preventive measures reducing the flow of water into the bucket. This would solve the issues just mentioned, but it would seem to be a somewhat ‘artificial’/non-parsimonious model.

Figure 2. Tipping-bucket model of feather pecking (Van Niekerk (2015); modified after Bracke et al. (2012)).

Figure 3. Balance model (Van Niekerk (2015), from http://www.henhub.eu/fp/mech/).

Perhaps the balance model could be modified to a balance between ‘fixed’ risk factors on the one scale and management (farmer effort) to reduce tb/fp risk on the other scale of the balance. However, the symmetry in disbalance suggested by the model does not seem to make sense: too much pressure on one side does not have the same effect as too much pressure on the other side. Also, fp/tb does not seem to be (totally) reversible: inducing fp/tb by removing a bit of enrichment cannot be undone by adding the same bit of enrichment (at least not shown). Also, to date no studies are available showing reversibility by adding other factors (e.g. inducing tb/fp by poor litter quality and then ‘treating’ this problem by adding e.g. better feed, etc.).

The next figure (Figure 4 below) shows a newly developed ‘face’ model aimed at incorporating the different types of animal involved (actor, victim, neutral), as well as emphasising the role of the farmer (as a kind of ‘actor’) in dealing with a fp/tb problem. The farmer is important for prevention and treatment of fp/tb. The emergence of an animal-actor is necessary to start fp/tb, but the responsiveness of the victim also plays a roll. For example, a victim may more or less effectively avoid becoming a victim and respond more or less in a way that leads to escalation of an outbreak. While a learning process may have transformed actors into individuals predisposed to show the abnormal fp/tb behaviour again at a later stage, similarly, at some point victims may show learned helplessness (which may also more or less permanently alter their behavioural predisposition).

Figure 4. New ‘face’ model of feather pecking (fp)/tail biting (tb), showing its multifactorial nature (‘left ear’), the role of different types of animal (actor & victim (‘eyes’), neutral (‘mouth’)), array of responses (‘right ear’), as well as the role of the farmer (‘nose’) in dealing with the problem. Both positive and negative feedback loops (‘glasses’ around the eyes of the face) are involved. Evolution and life history (‘hairs’) determine the set points of the individuals (animals and farmer). The comparators (‘pupils’ etc.) are (more or less) equivalent to welfare (smiley, balance, bucket and marble run) as indicated in the ‘necklace’ below the face. TIM: tail in mouth; OCTB: obsessive-compulsive tail biting; p.m.: pen mate; i.r.t.: in relation to. (Modified after (Bracke, 2017), and incorporating elements of the other models shown above, i.c. the balance and bucket models).

Reading guide

This was blog post nr. 5 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:

Introduction, specifying the need to compare feather pecking (fp) in layers and tail biting (tb) in pigs
Terminology, specifying the various concepts involved in fp/tb.
Overview of main similarities and differences between feather pecking and tail biting
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).
Models, reviewing available conceptual models of fp and tb, as well as presenting a new ‘face model’.
Disease framework, arguing that fp/tb may be regarded as a medical disorder, over and above being an abnormal behaviour per se.
Evolution and domestication, emphasising the need to view fp/tb as a phenomenon an evolutionary and genetic background.
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).

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

Introduction, specifying the need to compare feather pecking (fp) in layers and tail biting (tb) in pigs
Terminology, specifying the various concepts involved in fp/tb.
Overview of main similarities and differences between feather pecking and tail biting
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).
Models, reviewing available conceptual models of fp and tb, as well as presenting a new ‘face model’.
Disease framework, arguing that fp/tb may be regarded as a medical disorder, over and above being an abnormal behaviour per se.
Evolution and domestication, emphasising the need to view fp/tb as a phenomenon an evolutionary and genetic background.
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:

Introduction, specifying the need to compare feather pecking (fp) in layers and tail biting (tb) in pigs
Terminology, specifying the various concepts involved in fp/tb.
Overview of main similarities and differences between feather pecking and tail biting
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).
Models, reviewing available conceptual models of fp and tb, as well as presenting a new ‘face model’.
Disease framework, arguing that fp/tb may be regarded as a medical disorder, over and above being an abnormal behaviour per se.
Evolution and domestication, emphasising the need to view fp/tb as a phenomenon an evolutionary and genetic background.
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).

Towards a common conceptual framework and illustrative model for feather pecking in poultry and tail biting in pigs – 7. Evolution and domestication

This is post 7 on “Evolution and Domestication” 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

Introduction, specifying the need to compare feather pecking (fp) in layers and tail biting (tb) in pigs
Terminology, specifying the various concepts involved in fp/tb.
Overview of main similarities and differences between feather pecking and tail biting
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).
Models, reviewing available conceptual models of fp and tb, as well as presenting a new ‘face model’.
Disease framework, arguing that fp/tb may be regarded as a medical disorder, over and above being an abnormal behaviour per se.
Evolution and domestication, emphasising the need to view fp/tb as a phenomenon an evolutionary and genetic background.
References

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

7 Evolution & domestication

This final post/section aims to emphasise that adopting a disease framework for feather pecking (fp)/tail biting (tb) does not imply discarding the common science-based and evolutionary perspective on fp/tb. In order to show why this may be important we will first consider non-scientific reasoning to deal with fp/tb.

From a non-scientific and non-welfare perspective it may make perfect sense to farmers and veterinarians to prevent or treat fp/tb using respectively beak treatment (i.e. removing the means for fp) and tail docking (i.e. removing the object of tb). Similarly, measures like spectacles to prevent accurate vision (preventive measure in poultry) and teeth cutting (treatment measure in pigs) have been used, as has been the keeping of animals in the dark (thus blocking the animals’ vision). Along these lines one may also propose breeding poultry without feathers and pigs without tails, hens with blunted beaks, and pigs without incisor teeth, or perhaps blind animals (Ali and Cheng, 1985) (e.g. without eyes). Similarly, physical restrictions may be imposed in theory, e.g. solitary confinement/individual housing would be highly effective in stopping fp/tb. A related ‘solution’ is a limited physical ability to move (rather than lack of motivation (Bokkers and Koene, 2004)), as appears to be the case in heavily selected broilers. In fact, this may (partly) explain why fp is much less of a problem in broilers compared to laying hens. When comparing broilers to pigs, another reason, besides the limited physical activity, may be age. Broilers are slaughtered at 5-6 weeks of age, while egg-laying (puberty) starts at around 17 weeks (when severe fp normally develops). In pigs slaughter age and puberty are around 6 months and tb may be seen roughly in the period between 4 weeks and 6 months. Perhaps the situation in pigs, where tb is frequently seen in weaned and young growing pigs, and in rearing gilts but not in pregnant/farrowing sows, is somewhat more comparable to turkeys, where fp is a problem (5-8% in untreated turkeys; 10-16% in beaktreated turkeys) at around 4 days of age and around 8-10 weeks of age, at which age egg-laying/puberty may also start, while slaughter age is around 16-20 weeks (Van Niekerk and Bracke, 2016; van Niekerk and Veldkamp, 2017). Turkeys, like pigs, have been bred less intensively for muscle growth compared to broilers (Van Niekerk and Bracke, 2016). However, it may also be noted that fp in turkeys does not seem to respond as favourably to enrichment as does fp in laying hens (Van Niekerk and Bracke, 2016) and tb in pigs. In line with these considerations, the comparison between fp in poultry (laying hens and broilers) and tb in weaned/growing pigs, would raise the tentative suggestion that while fp is less prevalent in fast-growing broilers because of their very young age and limited physical activity, slower-growing broilers, in virtue of the older age and enhanced physical activity, should be expected to have an enhanced propensity to show fp behaviour. An anonymous poultry-welfare expert (pers. comm.) indicates that this may indeed be the case.

A risk of using breeding for inactivity to reduce fp/tb, of course, could be that in addition to reducing the propensity of the actor to show harmful social behaviour, inactivity may also reduce the propensity of the victim to avoid being pecked/bitten. Another breeding goal may thus be to select for animals that do not have the (cognitive) capacity to ‘discover’ fp/tb, and/or to breed against the ability to acquire the behaviour through social transmission (i.e. to learn from conspecifics who have become actors). Such selection for ‘stupidity’ is also unlikely to be effective, because both laying hens and pigs need a certain level of cognitive functioning and synchronisation, e.g. to regulate access to limited resources like nest boxes and feeders (Boumans, 2017).

A major factor in causing fp/tb is the animals’ motivation to explore/forage. Would it then make sense to select against this motivation per se?

In applied ethology it is commonly assumed that fp/tb are caused or at least mediated by a deprived motivation to forage. The idea is that poultry and pigs still have behavioural needs originating from evolution in a natural environment. Domestication is not perceived to have had a major attenuating effect, i.e. modern pigs and poultry are not (yet) adapted to intensive farming. The motivation to forage is still considerable because it was essential to survive in a natural environment spending considerable periods of time searching for food. Being generalist omnivores also implied these animals had relatively inquisitive natures to investigate a wide variety of potential food items under variable circumstances encountered in nature.

In fact, this attraction to novelty and eagerness to learn may well be sufficient to explain one of the most characteristic features of fp/tb, namely that a kind of irreversible state change occurs once the first fp/tb has taken place, and also that the problem has a certain tendency to escalate and is much more difficult to counteract later than it is to prevent it from occurring in the first place. A normal learning process can thus explain the difference in set point between animals who have never experienced fp/tb and those that have. No pathology need to be involved here.

Esp. pigs that are provided with novel enrichment materials clearly show ‘fanatic’, almost compulsive behaviours, except that the behavioural intensity tends to wear off readily (it is mostly a matter of a few quarters rather than hours that pigs spend on interacting with new enrichment materials). However, when the enrichment is slowly destructible (like soft wood), designed to fit the needs of the animal (e.g. branched chain design, (Bracke, 2017)) or provides (irregular) food rewards, e.g. as in the case of the Edinburgh foodball in pigs (releasing food pellets upon being rooted and thus moved around the pen (Young et al., 1994)), much more persistent (and less fanatic) interest may be observed. Pigs and poultry also clearly appreciate the taste of blood and (tail/feather/skin) tissue.

Note also that in addition to being potentially explained as a cognitive (learning) process, the escalation of fp/tb and (subsequent) state change may also be related to cognition and a tendency to show synchronised (feeding/exploration/activity) behaviour. A related potentially-involved mechanism could be the supposedly powerful tendency to show conformism, as suggested by De Waal in the case of primates (De Waal, 2016).

E.g. van de Waal et al. (2013) showed that green monkeys that had been trained to prefer maize of one colour, would unlearn their previous colour preference and acquire the colour preference of the group they had been introduced into. Similarly, mixing a less friendly primate species with a more friendly species, made the former much (4 times) more friendly (De Waal and Johanowicz, 1993). Uitdehaag et al. (2009) found that mixed housing of a more and less fearful strain of laying hens negatively affected fp and fear-related behaviour. Perhaps conformism may play a role in fp/tb in that once more and more individuals start to show the behaviour, other individuals may have a strong tendency to do the same. Thus conformism may explain (part of the escalation) by potentiation, but it cannot explain its origin (though it may explain why there is a reluctance to show fp/tb in a group that has never experienced it before). (Note: the origin may also be more or less accidental, e.g. McAdie and Keeling (2000) showed that (artificially) damaged feathers may trigger (outbreaks of) fp in laying hens.)

Counteracting the motivation to show fp/tb by genetic selection may simultaneously counteract the animals’ motivation to consume feed and thus (efficiently) produce under commercial conditions. Pigs and poultry need to be eager to consume food and they must readily accept novel feeds (e.g. when moved from rearing farm to finishing/egg-laying farm).

Thus, the motivation to forage may not only be a remnant of evolution in a natural environment, it may also be a product of selection for maximised production efficiency. In other words, domestication and genetic selection may have been co-shaping the current problem underlying fp/tb in intensive pig and poultry farming.

Traditionally, pigs and poultry have been selected using individual selection, i.e. the fastest growing individuals were selected to breed the next generation, perhaps even when individuals were showing high levels of production at the expense of pen mates (e.g. due to excessive aggression or the performance of fp/tb). In particular, when fp/tb occurred the (most heavily affected) victims were unlikely to be used for reproduction, but the actors in a pen could partly go unnoticed (unless they were detected and eliminated from the group). Group selection has been proposed as an alternative to individual selection, where the production efficiency of pen mates is also taken to load on an individual’s selection potential (Muir, 2003; Bijma et al., 2007a; Bijma et al., 2007b). Group selection has thus been suggested as a potential solution for fp/tb by selecting for peaceful pigs/poultry. Such peaceful pigs, however, may be less motivated to forage, and thus be less efficient for production.

Genetic selection probably has made use of the evolutionary tendency of animals (esp. males) to grow fast so as to have a higher likelihood of reproduction (as the largest individuals of a generation tend to win fights for access to females). Fast growth (as required for pigs and broilers), however, requires a persistent appetite to sustain growth. Compared to egg-laying in hens, which similarly require a substantial appetite to be able to sustain a high egg production, the biological prioritisation is different. Resource allocation theory suggests that animals make adaptive adjustments in the allocation of resources to different life processes when facing changed selection pressures (Beilharz et al., 1993). Hens must prioritise allocating energy to their offspring (eggs), whereas pigs and broilers must (i.e. have been selected to) allocate energy to their own growth (so as to produce meat). Thus, both types of farm animals are also likely to have been selected to prioritise (as much as possible) those processes that are preferred by man (be it the production of meat or eggs). Thus, when dealing with (mild) disease states it is possible that farm animals have been selected to (tend to) prioritise production over the (energetically costly) activation of the immune response. Farm animals that continue ‘functioning’ in an economic/zootechnical sense, however, may not be the most productive overall, e.g. when enhanced appetite has a negative side-effect in increasing the likelihood of fp/tb.

Several observations may be in line with the suggestion that in modern farm animals appetitive foraging motivation may have originated in a discrepancy with the natural environment, but may also have been co-determined by genetic selection for maximised production efficiency. A main indicator is that adult animals, esp. pregnant sows and broiler breeders, are known to experience high levels of feeding motivation and a tendency to become obese when given ad lib access to feed. (In laying hens, however, fp rather seems to be associated with hyper-mobility, also called a hyperactivity disorder (Kjaer, 2009), perhaps related to an (over-)activated foraging motivation.) In addition, when growing pigs are feeding they seem to be focussed so much on feed intake that vaccinating them with a rather painful (large diameter) needle seems to go (largely) unnoticed. Also, growing pigs whose front teeth have been cut so as to counteract an outbreak of tail biting don’t seem to show a clear reduction in feed intake. When their teeth have been cut, however, the pigs are much less inclined to continue tail biting and they also show much less interest in manipulating enrichment materials like chains, wood and ropes, suggesting that they do feel pain while maintaining a relatively high motivation to feed.

A final aspect where a science-based evolutionary understanding of fp/tb behaviour has clear added value over a classic medical framework may be the observation that not all kinds of stressors are equally likely to contribute to fp/tb. This may be an important aspect of the pathophysiology/mechanism underlying fp/tb. In laying hens, for example, organic farmers say that pullets with access to an outdoor range are less fearful later in life (e.g. in using the outdoor range), and therefore are less likely to develop fp (TvN, pers. comm.). Also in laying hens, the stressor of being moved from the rearing farm to the layer facility appears to be a trigger of stress and fp (even though it may also be a ‘revival’ of fp that originated at the rearing farm). In pigs, by contrast, mixing is not typically eliciting tail biting, despite the fact that it is highly stressful for the pigs. E.g. Holinger (2017) found no effect of mixing and isolation stress on tail and ear manipulation in pigs. Note also that mixing in pigs typically occurs at 25kg body weight (10-12 weeks of age), which is long before puberty at slaughter age, i.e. about 5-6 months of age, whereas laying hens are transferred to the laying facilities shortly before egg-laying starts (i.e. puberty). In pigs this compares to the rearing of breeding gilts, who are also particularly prone to tb (probably because they are fed on more restricted diets than slaughter pigs are), but only at a younger age (i.e. before the gilts are inseminated). Tb in pigs is hardly seen in (first or older parity) pregnant sows and in this respect tb in pigs differs from fp in laying hens. Such differences must be kept in mind, but they should not overrule the striking similarities between fp in poultry and tb in pigs, nor should they be regarded as a counterargument to the proposition that fp/tb would certainly benefit from being regarded as a medical/mental health disorder, provided the existing science-based and evolutionary framework is maintained to understand the behavioural as well.

Reading guide

This was blog post nr. 7 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:

Introduction, specifying the need to compare feather pecking (fp) in layers and tail biting (tb) in pigs
Terminology, specifying the various concepts involved in fp/tb.
Overview of main similarities and differences between feather pecking and tail biting
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).
Models, reviewing available conceptual models of fp and tb, as well as presenting a new ‘face model’.
Disease framework, arguing that fp/tb may be regarded as a medical disorder, over and above being an abnormal behaviour per se.
Evolution and domestication, emphasising the need to view fp/tb as a phenomenon an evolutionary and genetic background.
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).

Towards a common conceptual framework and illustrative model for feather pecking in poultry and tail biting in pigs – 8. References

This is post 8. “References” 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

Introduction, specifying the need to compare feather pecking (fp) in layers and tail biting (tb) in pigs
Terminology, specifying the various concepts involved in fp/tb.
Overview of main similarities and differences between feather pecking and tail biting
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).
Models, reviewing available conceptual models of fp and tb, as well as presenting a new ‘face model’.
Disease framework, arguing that fp/tb may be regarded as a medical disorder, over and above being an abnormal behaviour per se.
Evolution and domestication, emphasising the need to view fp/tb as a phenomenon an evolutionary and genetic background.
References

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

8. References

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Reading guide

This was blog post nr. 8 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:

Introduction, specifying the need to compare feather pecking (fp) in layers and tail biting (tb) in pigs
Terminology, specifying the various concepts involved in fp/tb.
Overview of main similarities and differences between feather pecking and tail biting
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).
Models, reviewing available conceptual models of fp and tb, as well as presenting a new ‘face model’.
Disease framework, arguing that fp/tb may be regarded as a medical disorder, over and above being an abnormal behaviour per se.
Evolution and domestication, emphasising the need to view fp/tb as a phenomenon an evolutionary and genetic background.
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).

Feather pecking & injurious pecking in organic laying hens in 107 flocks from 8 European countries

Feather-pecking and injurious pecking in organic laying hens in 107 flocks from eight European countries.
By Bestman, M; Verwer, C; Brenninkmeyer, C; Willett, A; Hinrichsen, LK; Smajlhodzic, F; Heerkens, JLT; Gunnarsson, S; Ferrante, V. 2017.
Animal Welfare, 26: 355-363(9).

Feather-pecking and cannibalism may reduce the potential of organic husbandry to enhance the welfare of laying hens. We report risk factors for these issues based on a large survey of 107 commercial flocks in eight European countries. Information was collected regarding housing, management and flock characteristics (age, genotype). Near the end of lay, 50 hens per flock were assessed for plumage condition and wounds. Potential influencing factors were screened and submitted to a multivariate model. The majority of the flocks (81%) consisted of brown genotypes and were found in six countries. Since white genotypes (19%) were found only in the two Scandinavian countries, a country effect could not be excluded. Therefore, separate models were made for brown and white genotypes. Feather damage in brown hens could be explained by a model containing a lower dietary protein content and no daily access to the free range (30% of the variation explained). For feather damage in white hens, no model could be made. Wounds in brown hens were associated with not having daily access to free range (14% of the variation explained). Wounds in white hens were explained by a model containing not topping-up litter during the laying period (26% of the variation explained). These results suggest that better feeding management, daily access to the free-range area and improved litter management may reduce incidence of plumage damage and associated injurious pecking, hence enhancing the welfare of organic laying hens. Since this was an epidemiological study, further experimental studies are needed to investigate the causal relationships.

Resource package reduces feather pecking and improves ranging in free-range layers

Provision of a resource package reduces feather pecking and improves ranging distribution on free-range layer farms

By Isabelle C Pettersson, Claire A Weeks, Christine J Nicol. 2017. Applied Animal Behaviour Science 195: 60-66.

Highlights

• The effect of a resource package on welfare was studied on 14 commercial farms.
• Shelters, pecking pans and wind chimes were installed following a baseline year.
• Shelters and pecking pans were used consistently by birds.
• Feather pecking decreased and range distribution improved.
• Some other welfare measures showed improvement.

Abstract

The effect of a resource package designed to reduce inter-bird pecking and increase range use was tested on fourteen free-range farms in the UK. The package comprised two types of objects intended to attract pecking behaviour: ‘pecking pans’ containing a particulate pecking block, and wind chimes; plus long, narrow shelters placed just outside the popholes, bridging a barren area 2–10 m from the house, with the aim of improving bird distribution on the range. We predicted that if the resource package succeeded in these aims, overall bird welfare would also be improved. Fourteen commercial farms were enrolled for this two-year study. Flocks were assessed for pecking behaviour, range use and general indicators of welfare at 40 weeks in Year 1 without the resource package. The resource package was then added to the same houses at the start of the next flock cycle in Year 2. The new flocks were assessed in the same way at 40 weeks with additional observations taken of their use of the resource package at 25 and 40 weeks. These additional observations showed that most aspects of pecking behaviour directed at the pecking pans remained consistent from 25 to 40 weeks although a reduction in substrate pecking frequency was seen (p < 0.001) and birds perched on the pan for longer (p = 0.033) and more often (p = 0.010) at 40 weeks. Although consistent within houses, wind chime use was very variable between houses, with pecking observed in only 8 of the 14 houses. The number of birds under the shelters increased from 25 to 40 weeks (p = 0.018), as did the proportion of birds that went under a shelter within 5 min of entering the range area (p = 0.021). Birds were more likely to use a shelter within 5 min if they exited the shed via a pophole within 10 m of the shelter rather than a pophole more than 10 m away at both 25 weeks (p < 0.001) and 40 weeks (p = 0.001).

A reduction in gentle feather pecking (p = 0.001) and severe feather pecking (p = 0.018) behaviour was seen when the resource package was provided in Year 2. Range distribution also improved, with a greater proportion of birds seen 2–10 m from the house (p = 0.023). Additionally, the proportion of abnormal eggs (p = 0.010), headshaking behaviour (p = 0.009) and the percentage of wet/capped litter (p = 0.043) decreased in Year 2.

Management tips to stop feather pecking

By Tony McDougal. Poultry World, 2 Oct., 2017.

The UK branch of the World’s Poultry Science Association held its annual conference in Cambridge this summer. Scientists looked at poultry feathers and skin – the past, present and future of poultry integument.

Management risk factors and genetic influences have an effect on feather pecking, according to the University of Bristol’s Christine Nicol.

…

Thea van Niekerk, from the Wageningen Livestock Research centre, Netherlands, adds prevention is most important as once feather pecking begins, the behaviour is very hard to stop.

Ms van Niekerk explains that optimising rearing conditions to prevent injurious pecking was the first step: “The most important strategy in rear is a continuous presence of good substrate to stimulate foraging behaviour and to teach the pullets to direct their pecking towards the litter.”

…

Esther Ellen and Piter Bijima, of Wageningen University Research Animal Breeding and Genomics centre, assessed genetic solutions to injurious pecking.

They argued that, while behavioural observations can be used to select against feather pecking, they were expensive, time consuming and difficult to apply in animal breeding. Instead, a solution could come from quantitative genetic methods that took into account both the direct (DGE, victim effect) and indirect genetic effect (IGE, actor effect).

“For the survival time, we found that the victim effect contributes 35-87% of total heritable variation. Together, they explain 15-26% of total phenotypic variation in survival time.

…

Professor Nicol’s joint paper with Dr Claire Weeks, ‘Provision of a resource package reduces feather pecking and improves ranging distribution on free-range layer farms,’ was published in the Applied Animal Behaviour Science in July.

Note: Read more on … in Poultry World.

Practice vs theory on the prevention of feather pecking in laying hens in non-cage systems

Are practice recommendations for the prevention of feather pecking in laying hens in non-cage systems in line with the results of experimental and epidemiological studies?

By Lisa Jung, Ute Knierim, In press. Appl. Anim. Behav. Sci.

Highlights

• We compared 15 practice recommendations with results of 108 empirical studies.
• On average each recommendation contained less than 50% of the 49 confirmed preventive factors.
• In total they also comprised 15 contentious and 12 not yet investigated factors.
• On this basis recommendations should be amended and further studies conducted.

Abstract

Feather pecking (FP) in laying hens is an important animal welfare problem in practice, despite extensive research and increasing sources of advice for farmers. We aimed to give an overview over results from experimental and epidemiological studies. We included non-cage systems, covering the rearing and laying phase. The investigated factors were categorised into those with either good, contentious or no evidence regarding preventive effects on FP. Moreover, we wanted to know to what extent recommendations for farmers are based on this scientific evidence. We extracted 62 potential preventive factors from 88 experimental and 21 epidemiological studies. 17 factors during rearing, and 32 factors during the laying phase significantly affected the risk to develop FP or plumage damage (PD). Factors were counted as significant if other studies found no or at most one opposite result. Seven factors during rearing and 16 factors during laying were confirmed by more than one study, with no or at most one opposite result. Provision of dry litter on the floor and sufficiently high perches during rearing and laying or a high use of the free range area during the laying phase were among these influencing factors. In the reviewed 15 practice recommendations, almost all of these factors have been taken up, although no recommendation comprises all factors and most miss more than the half of them. This leaves ample room for improvement of the recommendations. On the other hand, they altogether recommend 15 contentious as well as eight non-significant or 12 not yet investigated factors for which further scientific investigation is necessary.

Range cover for organic layers – Leaflet

Our new leaflet on novel range cover options within an organic poultry farming system is out (click on leaflet for the pdf).

Update on Poultry Red Mite at International Egg Commission’s conference in Bruges

Challenges and solutions in coping with poultry red mite

Delegates at the International Egg Commission’s conference in Bruges were given an update on the spread of poultry red mite, the ongoing scientific work and solutions to controlling outbreaks.