Towards a common conceptual framework and illustrative model for feather pecking in poultry and tail biting in pigs – 3. Overview

This is post 3 on “Overview of main similarities and differences between feather pecking and tail biting” 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.

3. Overview of main similarities and differences between feather pecking and tail biting

Table 1 shows an overview of similarities and differences between feather pecking (fp) in poultry (i.c. laying hens) and tail biting (tb) in pigs (i.c. weaned and growing/fattening pigs).

Table 1 is based primarily on Brunberg et al. (2016) and supplemented with our own (esp. MB and TvN) knowledge about fp and tb (also as presented on the henhub website www.henhub.eu). The table is intended to summarise the most relevant similarities and differences between fp (in hens) and tb (in pigs), and thus support decision making in dealing with fp/tb in practice.

The key risk in fp/tb is the fact that both laying hens and pigs are originally omnivorous generalists that have been become production specialists in feed intake and food conversion in intensive farming conditions. The motivation for fp/tb relates to a frustrated foraging need, which is modulated by a whole array of different risk factors, hence resulting in this multifactorial welfare issue. In addition to similarities the table also identifies a number of differences between fp in layers and tb in pigs, e.g. we don’t have genetically selected lines for tail biting comparable to the high and low fp lines in poultry. Hence, an experimental model to study tb in more detail is currently largely lacking (though pigs selected for social breeding value (high indirect genetic effects for growth) showed considerably less ear biting, tail damage, aggression and enrichment manipulation (Camerlink et al., 2015), and may thus in principle be suited to be used to study tb experimentally in more detail).

The table may perhaps be improved upon further by specifying relationships between the items specified as risk factors (in the left column) and the different responses identified in the process of fp/tb (in the right column; cf (Fraser, 1987a)).

Another suggestion relates to the many risk factors that may hamper practical problem solving. While scientific experiments necessarily vary only a few risk factors in order to reliably examine which factors may affect fp/tb, a tentative suggestion for solving the multifactorial fp/tb problem could be to try to formulate multifactorial solutions. This may be esp. relevant when monofactorial solutions fail to solve the problem. However, an important drawback of this approach is that it may essentially remain unclear which factors are accountable for any (positive or negative) results. When a multifactorial approach is working, it may be possible to tease out in subsequent research the relative contribution of the different risk factors. When it doesn’t work, that may be the end of the road for that particular type of farming (given the constraints imposed).

Table 1. Comparing risk factors and animal responses related to feather pecking (fp) in poultry (laying hens) and tail biting (tb) in pigs, taking Brunberg et al. (2016) as a starting point, supplemented with own author expertise (marked as *). Common risk factors (similar across species, specified between brackets when ‘unknown’) are followed by notable differences between Hens and Pigs (specified on the next lines). Black characters: risk increasing factors; green: risk decreasing factors (benefits); red (in the column ‘risk factors’): particularly welfare-reducing risk factors. ‘No’: means that the opposite reduced fp/tb.; behav.: behaviour; envir.: environment; decr.: decreased; incr.: increased; HFP: high fp line/breed; LFP: low fp line; TIM: tail-in-mouth; w: weeks; d: days; mo: months. The cells in column ‘Responses’ are not directly (horizontally) related to the risk factors. Responses are stacked: more positive behaviours are presented at the bottom; worst (form of escalation, i.e. cannibalism) is shown on top. Responses are related to ‘type of animal’ (victim, actor, neutral) (with welfare aspects specified at the level of the type-of-animal label). Poor welfare responses are shown in red (in the column ‘responses’). See the text for a more detailed description of how to read the table.

Type of factor	Risk factors (Multifactorial, related to the type of factor, i.e. environment-, group- & animal based)	Responses (behav., physiology, pathology & welfare, related to type of animal, i.e. victim, actor, neutral)	Type of animal
Envir.-based	Modern large-scale specialised farms	Victim: fear, pain (during outbreak), stress, sickness (during treatment, recovery)	Victim
	Barren pen (no proper foraging material, straw), large discrepancy between intensive farming envir. and the natural envir./envir. of evolutionary adaptation	Cannibalism
	(Partly) slatted floor Hens: (Litter) Pigs: Concrete	(Wound) infection
	Indoors* Hens: Range (may provide foraging opportunities and reduce stocking density) Pigs: – (Outdoor area may provide rooting substrate (soil), fibre (pasture), but not necessarily)	Production loss (reduced growth) Hens: Egg laying (reproduction) Pigs: Growth (production)
	One size fits all (food, climate*)
	Standardised feed, optimised for average individual (vs indiv. needs); perhaps probiotics may treat fp/tb Hens: – Pigs: No phase feeding; decr. feeding frequency predicted tb outbreaks 9 w later; tb victims made more feeder visits 2-5w prior to tb	Appearance Hens: Deteriorating feather cover Pigs: Tucked tails
	Feed changes and ‘hiccups‘ in providing feed (unpredictable frustration)	Decreased tryptophan, serotonin levels
	Feed type; Reduced feeding time, not ground, concentrated feed, less fibre Hens: Pellets give more fp than fine ground feed; no mash/pecking materials; high E diet; no feathers in diet (acting as fibre, incr. feed passage) Pigs: Contradictory results (liquid/pellets/meal) but straw reduces tb & is consumed	(Fp/tb) Wound(s) Hens: Esp. tail, body (not back of head) Pigs: Tail (possibly ears, flanks, legs)
	Protein, mineral (NaCl) deficiency; supra-nutritional NaCl may alleviate fp/tb Hens: Deficiency of crude protein, amino acids, minerals (Na, Ca) Pigs: Nutritional imbalance incr. tb
	Feeder space, feed competition (bite/peck to get access to feed)	Salivation (pH incr.; alleviate peptic ulcers)
	Rearing conditions (both poor rearing conditions and a backdrop from enriched rearing conditions to deprived conditions later in life) Hens: Absence of litter around 5w, high stocking densities, rearing on wire floor Pigs: More piglets/stockperson, fostering, no straw in farrowing pen, reduced feeder space during rearing gives more tb later in life; multi-litter rearing decr. manipulative behav.; providing straw during rearing and then depriving pigs of straw later is also considered a risk factor	[Microbiota composition?] Hens: HFP has different microbiota composition than LFP; feather eating changes gut microbiota; Pigs: Unknown
	(Pen size, pen design) Hens: (Large) Pigs: (Small)	Escalation of tp/tb (outbreak)
Group-based (envir.- & animal based)	Group housing Hens: (Very) large groups (10-100.000 birds) Pigs: Small (~10 pigs)	Arousal, restlessness, excitement (positive), fear & avoidance (negative). Hens: Cut feathers increased fp Pigs: Blood tail model (rope) increased (tail) biting behav.
	High stocking density Hens: More fp in largest groups (15-120 birds) Pigs: (Not uniform results)	Cognition, (social) learning, (synchronisation; copy-behaviour; stimulus enhancement)
	Farm health status (any (major) stressor/immune suppressor probably) Hens: Vaccination (specific immune stimulation) when young may incr. fp as adults; LFP have better immunocompetence; e.g. E. Coli incr. severe fp Pigs: Better health status reduces tb; straw reduces infections	Prevalence/intensity: Hens: Fp on 86% of UK flocks; SFP esp. when adult; fp up to 135 bouts/bird/hr; 3 severe pecks/min Pigs: Tb on 30-70% of farms; fanatic biters bite 11-25% of time
	Mutilation (3 aspects are relevant: 1. Method used; 2. Amount of tissue removed; 3. Age of treatment; esp. 2nd aspects is relevant as risk factor) Hens: Beak treatment (previous beak trimming (may remove larger/smaller part of the beak), now infrared beak treatment) (Note: In poultry, as it were the (future) actor is mutilated)	Severe fp (SEP)/tb Hens: – Pigs: Three types of (severe/injurious) tb: two-stage (starting with TIM), sudden forceful, and obsessive (fanatic)
	Pigs: Tail docking (longer or shorter part of the tail) (Note: in pigs as it were the (future) receiver is mutilated by removing the tail)	Actor: (Excitement, pleasure [during outbreak], pain, stress [during treatment]) Hens: Pecker Pigs: Biter	Actor, performer
	History of fp/tb (once an outbreak has occurred, the likelihood of another outbreak increases; animals are never the same again after an outbreak; (irreversibly) changed set points)	Object-direction: Hens: Towards feathers Pigs: Towards the tail
Animal-based	(Bred for) very high production-efficiency (genetics, breeds) (esp. genetic motivation of feed-related behav.; behavioural need to species-specific foraging behav); fp/tb has moderate heritability (~0.2)	Neutral (in same pen)/control (on other pen): Neutral as a biter in spe: boredom, frustration, behavioural deprivation, esp. of foraging motivation	Neutral / control
	Hens: (Eggs) Pigs: Lean meat; neutrals have different genetics	Gentle manipulation Hens: Gentle fp is prevalent in young birds, decr. with age Pigs: Tail in mouth (TIM),
	Domesticated 5-6000 years ago; bred in 50 years of intensive selection from foraging generalists (omnivorous (variable diet; need to explore)) to meat & egg producing specialists; fp/tb not selected against; tb&fp are correlated to production, but not in the same way	Pen-mate directed exploration Hens: (Deteriorated) plumage condition Pigs: Wet tails
	Hens: Male peckers had higher body fat; female peckers had earlier onset of lay; HFP: Better growth, lower total egg mass, decr. feed efficiency Pigs: Lower backfat, lean tissue growth	Consummatory behav.: Hens: Feather eating (more in HFP) Pigs: –
	Being different Hens: Plumage colour (standing out from others; incidental pigmented birds were more often victims) Pigs: [Lame pigs get bitten]	Object/substrate-directed exploration/foraging in accordance with nature, showing natural behav. (50-60% of time) Hens: Scratching, pecking Pigs: Rooting, biting
	Personality Hens: Peckers appear more proactive, fearful (in open field), stress (cortisol shows variable results); more foraging & walking when young incr. fp as adults; HFP more active; mobility to get to the nestboxes (i.e. too calm birds are at risk for fp) Pigs: Low backtest responders showed less pen-mate manipulation; biters more sitting & kneeling 6d prior to tb; victims more posture changes 6 d prior to tb; tail posture (tucked) may predict tb 2-3d before outbreak
	Sex, probably females more active performers Hens: All females Pigs: Mixed/uni-sex; males receive more tb; uncastrated males are more likely to become fanatic biters (1 study)
	Age: Onset around sexual maturity (also then shifting nutritional needs) Hens: Adult (16-80wks); progesterone (& oestrogen) incr. up to 18w incr. fp; testosterone decr. fp; SFP ~20w in females, but not males Pigs: Young, prepubertal (<5-6mo); perhaps associated with teething*
	Body weight Hens: – Pigs: Biters are lighter; victims tend to be heavier before tb (later decr. growth)

Reading guide

This was blog post nr. 3 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).