thuispagina

Advantages and disadvantages of different housing systems for the welfare of laying hens

Disadvantages in all systems
There are some management practices or conditions that reduce welfare in all or most systems and they include the following:

• Beak trimming
  Beak trimming is still widely used in many EC countries (although prohibited in some) to reduce the risk of pecking injuries and mortality, and there is good evidence that this practice is painful, and depending on methodology, can be chronically painful over a prolonged time as well as being acutely painful (Hughes and Gentle 1995). The principal disadvantage is that all birds are treated to reduce the possible (not definite) risk to welfare of some of the flock. Victims of severe feather pecking and cannibalism may suffer more than if they were beak trimmed (although this has for obvious reasons not been scientifically examined), but the goal should be to design and manage systems (particularly rearing systems) and to select genotypes to minimise the risk of agonistic behaviour. Birds housed in larger groups are most likely to be beak trimmed, so the risk of mutilation is lower in small cages. A previous epidemiological study in the UK of brown feathered genotypes found risk factors associated with outbreaks of feather pecking included the use of bell drinkers, several changes in diet, absence of loose litter at the end of lay and a temperature in the laying house of below 20^oC (Green and others, 2000). These factors did not necessarily cause or promote feather pecking, and it is still not understood what triggers this behaviour in hens. More recent UK data on Shaver 579 Leghorn hens in commercial units found that the incidence of both gentle and severe feather pecking was reduced as group size increased (from 2450 to 4200 birds/flock) and where bell drinkers rather than nipple drinkers were provided (see 4.6 for details).

• Skeletal weakness
  The high productivity of the modern laying hen causes osteoporosis that is compounded in conventional cages by disuse osteoporosis, but present to a sufficient degree in all systems to present a substantial risk of fractures during handling at the end of lay. Recent evidence suggests that a high proportion of birds sustain keel bone fractures in all systems (compounded in non-cage systems by risk of crashing) at some point during the laying period.

• Bumble foot
  This is a variable risk in all systems that provide perches (thus rare in conventional cages). Risk is reduced by good hygiene and keeping the feet of birds clean from mud and faeces, as well as by good perch design. Although generally of relatively low prevalence, welfare of affected birds in its acute stage is compromised by inflammation and severe swelling of the foot pad making normal walking and perching impossible.

Conventional cages
The evidence from this report has in the main substantiated previous scientific knowledge that the welfare of laying hens is severely compromised in conventional cages (for example, see review by Baxter, 1994).

• Disadvantages
  The main disadvantages are discomfort and abnormal behaviour which are inherent to the system. The design of the system does not allow birds sufficient space for exercise, thus restricting or preventing behaviours such as wing flapping and flying, and leading to disuse osteoporosis that renders birds susceptible to fractures on depopulation. Our current knowledge indicates that the most important deficiency from the birds’ perspective is the lack of provision of a discrete, enclosed nesting area. Nesting is a behavioural priority for hens. Moreover perching, dustbathing and foraging are also very important parts of the normal behavioural repertoire that cannot be (fully) expressed in conventional cages. Birds will work to gain access to perches at night, so lack of prevision of perches denies normal roosting behaviour for a substantial proportion of the whole day. There is some evidence that hens in conventional cages have insufficient space to maintain a normal ‘personal space’ and to escape from bullying by companions. Physiological stress levels are also higher in birds subject to spatial restriction.

• Advantages
  The main advantages are relatively low risk of disease and parasitism associated with better hygiene than many other housing systems.
  The small group size generally leads to a stable social hierarchy and lower risk of damaging feather pecking, cannibalism and smothering. The absence of litter in the system and the separation of birds from their faeces are usually associated with improved hygiene with cleaner eggs, low levels of parasitism (internal and external), bumble foot and reduced aerial pollution. Despite having fewer crevices for red mites to lodge in, outbreaks of infestation can occur, which is why the cell in Table 7.7 is coloured orange. Whilst mortality is on average lower than in other systems, outbreaks of cannibalism and disease are still possible, and these can create significant welfare problems. This was the case in one trial in our study, which increased overall average mortality for LayWel to higher levels than industry average, owing to the small dataset. There is negligible risk of predation, as the birds are completely enclosed in wire cages. Restriction of movement and lack of perches leads to a low risk of keel bone deformation and of fractures during production.

Furnished cages

• Disadvantages
  The disadvantages of furnished cages do not appear to be inherent to the system but depend more on specific design, features, genotype and group size. Thus, risks of feather pecking and cannibalism leading to high mortality are increased in brown-feathered genotypes than in white hens and may increase with group size, especially in non beak trimmed birds, although recent UK data from cages of 40 and 60 hens suggest that mortality can be low (Elson, 2005, personal communication). Whilst the behavioural repertoire is significantly improved in comparison with conventional cages, aspects may not be considered to be normal. The low proportion of hens performing foraging behaviour and the absence of complete dustbaths in furnished cage systems indicate that the substrate areas in these systems do not fulfil the needs of the hens, confirming the results of earlier studies in furnished cage systems. Birds make use of the perches during the day for substantial (around 40-50%) amounts of time, and this is associated with keel bone damage (LayWel data; Vits and others, 2005). There are insufficient data to compare levels of keel bone deformity with those found in non-cage systems, nor is it established whether the condition has a detrimental effect on bird welfare. Hens kept in any of the four small furnished cage models compared did not differ in level of feather pecking or aggressive pecking. However the use of dustbaths varied between averages of 21 and 81% depending on cage model (see 4.6). Thus there clearly is a need for more research and development in design of furnished cages and implementation of current knowledge, reviewed by Tauson (2005).

• Advantages
  Furnished cages retain many of the advantages of conventional cages without the drawback of severe behavioural restriction. The main advantages are better hygiene than most non-cage systems, so on average use of preventive drugs including coccidiostats is low, reflecting a low risk of infection with parasites or other infectious agents. Mortality is generally low, particularly in well-tested designs, and with experience of managing FC. High mortality can occur, particularly with some non-beak trimmed genotypes. Plumage is generally clean, but there is a variable risk of bumblefoot and red mite infestation. Although variable, up to 100% use of nestboxes in small furnished cages was recorded indicating that when well designed and managed, the systems meet the behavioural priority of hens for a discrete enclosed area for laying. Both bone strength and the behavioural repertoire are significantly improved in comparison with conventional cages.

Non-cage systems

• Disadvantages
  The main disadvantages are highly variable risks of feather pecking and cannibalism, leading in a few flocks to extremely high mortality and poor bird welfare. Mortality in well-replicated LayWel studies varied between a low 1.1% and a high 36.8% in single tier systems (ST-NC) with a similar range of between 2.2% and 35.3% in multi-tier systems (MT-NN). More research and refinement of system design and management is needed to prevent the high levels of mortality.
  There is a high risk of hens sustaining fractures, with recent studies indicating about half the birds are affected (Wilkins and others, 2004; Nicol and others, 2006). The timing and causes of these fractures is poorly understood but is likely to include collision damage with perches, nestboxes and other structures.
  There is a risk of subordinate birds having reduced access to feed, water (and range) due to bullying by dominant hens.
  The risk of smothering is increased compared with small group (cage) systems.
  The risk of internal parasites is relatively high in litter-based systems and very high in those with outdoor runs, but the use of anthelmintics and coccidiostats can limit the burden and thereby ensure good welfare for the birds, if their use is permitted.
  There is a risk from predation that can be minimised with the use of electric fencing and shelter for example.
  There is an increased risk of disease due to contact with droppings and in free-range systems due to contact with wild birds as well (e.g. this is thought to increase risk of contracting avian ‘flu).
  Aerial pollution tends to be high in litter-based systems and this can not only increase the load of infective agents but also depress the immune system. Good ventilation and reduced stocking rates can reduce the risk of problems.
  House layout and equipment can often make inspection and catching of birds for treatment and at depopulation more difficult.

• Advantages
  The main advantages are a greater opportunity to express the full behavioural repertoire, especially foraging and particularly in free-range systems. Although variable, up to 100% use of nestboxes was recorded indicating that when well designed and managed, the systems meet the behavioural priority of hens for a discrete enclosed area for laying. Hens have the freedom to exercise, including wing-flapping and flying and this increases bone strength.

Increased space availability can give submissive hens the opportunity to avoid aggressive birds.


Overall welfare impact

With the exception of conventional cages, we conclude that all systems have the potential to provide satisfactory welfare for laying hens. However this potential is not always realised in practice. Among the numerous explanations are management, climate, design, different responses by different genotypes and interacting effects. For example there was different use of nestboxes in furnished cages by different genotypes. The design of small furnished cages also had a significant impact on dustbath use.

All cage systems tend to provide a more hygienic environment with low risk of parasitic disease. There is possibly a high risk of poor welfare on a flock basis in all systems with larger group sizes (above approximately 10-15 birds) from damaging pecking and cannibalism. All laying hens also are at high risk from sustaining fractures both during the laying period and at depopulation. There is evidence that both these problems are associated with genetic selection for high productivity. Some existing genotypes (mainly white feathered) show a lower tendency for damaging pecking. Much greater emphasis should be placed on selecting genotypes with reduced damaging feather pecking tendencies for use in alternative housing systems for laying hens. Recent studies have shown that bone strength can be improved in laying hens by selection over only one or two generations without a great decrease in productivity (Fleming and others, 2005). For good laying hen welfare it is a priority that action be taken to reduce the current unacceptable level of fractures sustained during the laying period in all systems apart from conventional cages. This is likely to involve a combined approach of selective breeding, plus refinements to design and management including lighting.

Conventional cages do not allow hens to fulfil behaviour priorities, preferences and needs for nesting, perching, foraging and dustbathing in particular. The severe spatial restriction also leads to disuse osteoporosis. We believe these disadvantages outweigh the advantages of reduced parasitism, good hygiene and simpler management. The advantages can be matched by other systems that also enable a much fuller expression of normal behaviour. A reason for this decision is the fact that every individual hen is affected for the duration of the laying period by behavioural restriction. Most other advantages and disadvantages are much less certain and seldom affect all individuals to a similar degree.