Despite domestication and intensive genetic selection, commercial poultry retain the need to perform their natural behaviours. Conventional broiler housing often provides little opportunity for a good range of natural behaviours, while conventional layer cages severely restrict normal movement and behaviour. Damaging behaviours have been shown to increase in chickens when they are deprived of natural behaviours or sufficient amounts of stimulation. 1 This paper will review key behaviours of poultry and associated production, economic and welfare implications, as well as the benefits of enrichment, particularly for broilers, and of cage free housing for layers.
Damaging behaviours - in commercial poultry systems
FeatherWel 2 , a collaborative project led by University of Bristol, defines injurious pecking as ‘an umbrella term which covers four behaviours; gentle and severe feather pecking, vent pecking and cannibalistic pecking’. Injurious pecking occurs in commercial layer systems and essentially involves normal pecking redirected to another bird. If foraging, dust-bathing or exploratory substrates are unavailable or less attractive than the feathers of a neighbour, then pecking may be directed instead to feathers 3 . In addition, there are a range of other substantiated risk factors such as inadequate protein, fibre, feed as pellets (rather than mash), early social experiences, lack or brooding, poor pecking and litter substrates during rearing and adult periods, multiple diet changes, and fearfulness of birds. Vent pecking, may occur spontaneously, and independently of other feather pecking. The risk of the more serious types of injurious pecking increases as birds come into lay, and while similar rates may occur in caged and non-caged systems, the behavior may spread more widely in non-cage systems 4 . As well as leading to culling losses, the FeatherWel project highlights the economic consequences as birds with poor plumage cover have less thermal insulation, and bald chickens need up to 40% more feed to maintain body temperature. Increased susceptibility to disease can be associated with the stress of injurious pecking and the direct introduction of disease through pecks on damaged skin.
Routine beak trimming to reduce the impacts of injurious pecking affects the bird’s most sensitive organ and is painful. It incurs a cost to farmers and remains controversial despite refinement with infrared devices. Some countries have already banned the practice, with successful efforts to reduce the risks of injurious pecking. Meanwhile Wageningen University 5 is conducting trials without beak trimming on farm, as the practice will be banned in the Netherlands from 1 st September 2018.
Restricted foraging, chronic hunger and aggressive male behavior may play a role in feather loss of female broiler breeders, which has associated production and welfare implications. Prevention also requires better housing conditions during feather development with careful review of nutritional, temperature and joining management, as well as feather loss scoring and monitoring 6 .
Broilers reared under commercial conditions show a reduction in activity from 3 weeks of age and high levels of inactivity with 60-80% of their time spent resting 7 . This may also be associated with increased stocking rates and has been linked to increased incidence of leg problems 8 . High levels of inactivity are also significantly correlated to fat levels 9 10 . Exercise may reduce the impact of leg problems in broilers by increasing muscle strength. Consequently, this can have economic benefits by reducing the financial losses caused by culling and carcass downgrades 11 12 .
Natural behaviors – the benefits of nests, enrichment, cage free barn systems
Combined with adequate three-dimensional space and other management factors, enrichment can be an important factor in satisfying poultry behavior in commercial housing. Enrichment can be defined as an “improvement in the biological functioning of captive animals resulting from modifications to their environment”, evidence of which may include increased reproductive success and improved health 13 . Enrichment is often incorporated to encourage animal-environment interactions and improves health, welfare by promoting normal activity and natural behaviours. The provision of enrichment should enable social, physical, occupational, sensory and/or nutritional stimulation, and may also ensure more effective space utilisation, encouraging a more even distribution of animals, as well as reducing disturbances and aggressive interactions 14 . Enrichment may consist of point source items or bedding/flooring substrates.
The most fundamental physical enrichment for laying hens is a nest box. Providing an appropriate nest substrate is also important to allow for nest-building behavior. Neither is provided in conventional layer cage systems. Laying hens that are not provided with a nest site may show agitated pacing, interpreted as evidence of frustration, during the nest-seeking phase of laying 15 . Enclosed, nesting sites (eg. nest boxes) are strongly preferred over open nests.
The benefits of suitable dry litter flooring for basic comfort and dust bathing behavior are well established. Deep litter bedding also reduces rates of injurious pecking in layer flocks 16 . Suitable perches, manipulable and pecking objects, food variety, and variation in placement and sounds, all encourage animal-environment interaction (visual, tactile, olfactory or auditory stimulation) 17 .
Provision of objects to scratch, climb and perch on has been shown to contribute to improvements in leg condition in broilers 18 19 . The provision of perches can reduce effective stocking density and thereby reduce agonistic encounters. Perches can provide a means of escape from aggressive and feather pecking encounters, reduce fearfulness and also provide an increased use of the environment. Perching is a highly motivated behaviour in laying hens and they will spend a large proportion of their time perching if perches are available 20 . In egg- laying flocks perches can aid in reducing feather pecking and the number of floor eggs, as well as improving activity levels and calcium metabolism 21 .
Providing (low) perches for broiler chickens can also have benefits to their welfare, by allowing the birds the opportunity to exert some control over their environment. The greater the accessibility of perches the greater the perch use 22 23 . Bizeray et al. (2002) showed that lying time decreased in broilers who were given access to perching, as they spent more time perching. The location and height of perches was also found to be important for encouraging birds to interact with their environment. Perching behaviours (accessing perch and maintaining balance) enable birds to exercise the musculoskeletal system in a different way to walking, thus contributing to a reduction in leg abnormalities.
Multi-tier layer systems are designed to exploit perching behavior positively, and make efficient use of housing space. These systems inherently encourage movement and socialization by choice, further aided by suitable lighting and attraction to outdoor access. These systems are widely used in parts of Europe and Australia. It is important to note that birds are trained to perch and feed at increasing heights during the rearing phase. Keel bone fractures may be significant in the adult system though the use of suitable ramps, from one tier to another, has been found by producers to dramatically reduce these fractures and more research is being done in Switzerland. Recent research identifying suitable angles and features between tiers aims to reduce keel damage. Ultimately cage free systems that are designed around the behavioural needs of laying birds have had the lowest rates of mortality, fractures and injurious pecking. An example is the Rondeel® 1 system 24 . There is a lot of information on lighting regimes, types and intensity of light for production purposes, which is beyond the scope of this paper. However we note the association of lighting and its positive effect on bird activity and leg strength, and that light and dark periods are not only part of poultry behavioural needs but enable greater productivity. Twenty four hour periods of darkness have long been banned and replaced with more productive practices in developed countries. Natural light also provides a range and changing illuminance and encourages greater activity and exploration 25 . We have also found solar tunnels/tubes to be effective for provision of natural light in hot climates, also conveying a cost reduction over time.
Similarly there is a lot of information about spatial and social distribution which relates also to resource competition and conjecture about whether birds form sub-groups in large commercial flocks. While, this is again beyond the scope of the paper, experts note that non- cage systems provide more opportunity for escape and retreat, which allows them to move away from troublesome conspecifics 26 . There is also a range of research demonstrating that the provision of vertical heating and curtains (known as ‘dark brooders’) simulate maternal care and brooding in rearing houses improve commercial rearing and welfare of chicks 27 and reduce fearfulness, feather pecking, cannibalism 28 . Dark brooders can also reduce heating and potentially feeding costs.
Covered areas enable retreat for adult birds and also improve the use of space and reduce stress levels with consequential production benefits. Leone and Estévez (2008) showed that 2% increase in productivity was achieved via increased egg production and hatchability by providing enrichment in broiler breeder houses in the form of cover panels. Floor eggs were also reduced and male birds covered a larger area of the house, mating with more females. Economic gains (in 4.5 additional chicks produced per hen per cycle) from providing this enrichment in this commercial context were reported at approximately $3.3 million per year 29 .
Reducing fearfulness and panic
Fearfulness has a negative effect on welfare and also on productivity where sudden or prolonged fear can cause pain, injury and distress due to panic responses. Fearfulness is also associated with injurious pecking. Smothering, bone fractures, scratching and bruising as a result of panic responses can result in productivity impacts due to mortalities and downgraded carcass quality. Poor knowledge of poultry behavior and inhumane catching techniques can further increase these effects. Poor attitudes and stockmanship have been associated with the variation of peak lay among a number of commercial layer farms and reduced feed conversion efficiency in broilers 30 . Research also indicates that fearful birds show poorer growth and decreased feed efficiency and can impact on management due to difficulty in handling. This cost of reduced feed efficiency has previously been estimated to add an extra £5 million on to the annual feed bill for the UK broiler industry and twice that for the egg industry 31 . Conversely, good stockmanship can improve production and cost-efficiency, and may be one of the most important management factors 32 .
Enrichment can also reduce fearfulness and flightiness in response to novel stimuli and/or humans. For example, music can have positive effects on the stockperson’s attitude to work and consequently improve their care of the animals, as well as adapting the animals to regular noise. The results of research investigating the direct impact of music to reduce fearfulness in poultry are variable. Enrichment could also be used to reduce other potential responses to fear, such as smaller smothering events which appear to be associated with birds seeking shelter or cover 33 and cumulatively represent significant mortalities for farmers.
RSPCA welfare standards for broilers 34 provide specifications for broiler housing, management and enrichment based on scientific review. AssureWel 35 provides validated on- farm welfare assessment templates and a feather loss benchmarking tool. FeatherWel 36 provides a range of advisory guides and recommendations for prevention of feather loss and injurious pecking based on substantial research and validation on over 100 commercial flocks.
In conclusion, understanding poultry behaviour can reduce a range of negative welfare and productivity impacts, lead to the development of better farming systems and improve end products. Provision of good management of light, space, substrates, diet and suitable enrichment can encourage foraging behavior and promote increased activity within housing, contributing to improved leg health, litter quality and reductions in rates of aggressive behaviours, injurious pecking, breast burn, hock burn and pododermatitis 37 . Similarly, multi- tier layer systems offer a more complex three-dimensional housing system than cages with good production 38 , welfare and cage-free marketing opportunity plus the versatility of additional verandah or outdoor range options. Harmonising housing and management with poultry behaviour has a realm of welfare, production and economic benefits, while enabling poultry industries to align with existing and future ethical, social and market expectations.
1 Leone, E.H. & Estévez, I. (2008) Economic and welfare benefits of environmental enrichment for broiler breeders. Poultry Science 87:14-21
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24 Nicols, C. J. (2015) The behavioural biology of chickens. Cabi. Chapter 9: 163-182.
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