After the ban of conventional cages for laying hens in the European Union there was a rapid development of alternative systems. While furnished cages have replaced conventional cages in most EU countries, there are problems of acceptance of eggs from furnished cage in some countries, and the producers changed to non-cage systems: barns, aviaries and free range. There exist obviously different opinions among the countries on the state of welfare in furnished cages and non-cage systems. Furnished cages provide structural elements, such as perches, scratching areas and nests, which are considered essential for the behavioral wellbeing of the birds. However, these structures are presented under restricted conditions. There is also no deep litter available. The larger space for movement is mainly obtained by increasing group size and to a lesser extent to stocking density in both, non-cage systems and furnished cages. Large group size is known as risk factor for feather pecking and cannibalism. There is also a high incidence of bone breakage in non-cage systems. These aspects have to be considered when appraising the welfare situation in the different systems. The present study summarizes the state of knowledge on the most important welfare issues: Stocking density and group size, use of perches, litter, nests and free range.
Keeping laying hens in conventional cages has been banned in Europe for animal welfare reasons as of the end of 2012. This then has initiated the development of highly variable alternatives in the EU countries. While furnished cages have replaced conventional cages in most European countries, loose housed systems (deep litter and aviaries) have been chosen in Austria, Germany, the Netherlands and Sweden as the main management system. The rationale for the replacement of conventional cages through floor systems in Germany was the reluctance of the main retailers to sell eggs from cages hens. The EU marketing regulation has only one code for eggs of both, enriched and conventional cages. Since eggs from conventional cages can still be imported from non-EU countries, the retailers considered it too difficult to communicate the difference between both systems.
In addition, in the consumer’s perception aviaries and free range systems are generally assumed to be more animal friendly than furnished cages. This opinion is not shared by scientists and veterinarians, and recent reports in public media raised concern about the state of welfare loose house systems including organic egg production. In the following I will deal with the most important welfare issues in furnished cages, deep litter indoor systems and free range.
Stocking density and group size
High stocking density (350 – 450 cm²/bird) in combination with the small group size (4 – 5 birds) in conventional cages represents an extreme restriction of the total space for movement. Indeed the total space available has been identified as the most important factor influencing the movement of laying hens (Mallapur et al., 2009). The EU regulation for furnished cages, which replaced conventional cages as of 2013, provide considerably more space per hen (750 cm²), and commercial furnished cages are designed for 10 to 90 birds. This increases the total space available from about 2000 cm² in conventional cages to 7,500 – 68,000 cm² in furnished cages. The increase of total space through increasing group size is not generally considered an improvement of the bird`s welfare. The rational of the development of furnished or enriched cages was to combine the advantages of conventional cages, such as hygienic conditions and small group size, with those of deep litter systems, namely perches, scratching area and nest sites (Elson and Tauson, 2012). The risk of aggressive encounters and feather pecking and cannibalism increases with increased group size (Robinson, 1979). The trade-off of freedom to move and the risk of damages seem to be differently appraised in different countries. In Germany for instance, the law for the protection of animals gives a minimum total space per cage of 2.5 m² and a minimum area per bird with nest area of 890 cm². This results in a minimum group size of about 28 birds. In contrast, the legislation in Sweden and Denmark fixed the maximum group size in furnished cages to 16 and 10 birds respectively. The scientific basis of a minimum total space or a maximum group size in furnished cages is rather weak. Appleby (2004) is of the opinion, that 800 cm² per bird with eight birds per group are required to allow the birds sufficient freedom to perform the essential behaviors. Guinebretrière et al. (2009) reported more visits to the nests and higher use of perches, but no effect on dust bathing behavior with 60 birds per group as compared to 40 and 20 birds per group. Keeling et al., (2003) found a curvilinear effect of group size on welfare related traits with an intermediate size of 30 birds as more problematic than smaller or larger groups. This effect however, was mainly related to the social behavior. Severe feather pecking, feather damages and fear were higher at the highest group’s size in earlier studies (Bilcik et al., 1998; Bilcik and Keeling, 1999; 2000; Nicol et al., 1999). There was no cannibalism in furnished cages with groups up to 16 birds (Wall, 2003; Guedon and Faure, 2004). In beak trimmed hens the mortality was low even in groups of 60 birds (Huneau-Salaün et al., 2011). But recent large scale experiments using groups of 30 and 60 non-beak trimmed birds in different commercial furnished cages showed high levels of cannibalism (Anonymous, 2012). This has not only been attributed to high group size but also high light intensity. Group size in furnished cages is still considerably lower than in non-cage systems.
It is well documented that the risk of mortality through damaging pecking is higher in barns, aviaries and free range (Blokhuis et al., 2007; Sherwin et al., 2010; Elson and Tauson, 2012) and the large groups are considered as the main causal factor.
There is a sudden change of stocking density and group size when pullets are transferred to the layer facility. Stocking density at the end of the rearing period comprises 15 to 20 birds per m² and – according to the EU regulation – 9 birds per m² in the layer house. There is a routine established that after transfer to the layer house the birds will not receive access to the total space. The litter area, which represents about one third of total space will be closed. This is to ensure that all birds will find feed, water and nest sites. The stocking density in this stage is similar to the pullet rearing condition but higher than laid down in the regulation for laying hens. This practice is tolerated in the EU for the time before the onset of egg laying, but in many cases there is an extension for several weeks. There are reservations against the restriction of floor space and access to the litter and in some countries. In Sweden it is prohibited for welfare reasons. Recent unpublished experiments have shown, that the deprivation of space and litter from 16 to 18 weeks of age had no negative effects on production mortality and welfare criteria of laying hens. Further studies are needed to clarify the welfare implications of the reduced floor space and deprivation of litter in the transitional phase from the pullet to the layer housing.
The importance of litter
Litter material is considered an important stimulus for scratching and dust bathing in laying hens and lack of litter was a main reason for the ban of conventional cages. The EU regulation for furnished cages requires opportunities for scratching and pecking, but there is no specific information on size of scratching area and type and quantity of litter. Most of the furnished cages do not provide deep litter. There exist scratching areas of highly variable size, from extremely small solid plates of plastic to large areas of plastic or rubber mats. At the time being feed as pecking and scratching substrate is being distributed automatically in regular intervals. This solution is compliant with the wording of the EU regulation. The birds are using system intensively for scratching and pecking, but the question is raised, whether the need for dust bathing is satisfied as well. It is obvious, that the small amounts of feet do not allow the transport of dust into the feathers. The birds often are observed to perform dustbathing on the wire floor outside the scratching area while pecking in the delivered substrate. This type of dust bathing is being called shame dustbathing or vacuum dustbathing. This behavior not only occurs under restricted area and material in furnished cages but also when sufficient substrate and space are available (Vestergaard et al, 1990 Smithet al., 1993; Olsson et al, 2002). Dust bathing sequences in furnished cages are shorter and do not comprise all elements of a complete dust bath as in deep litter (Louton, 2014).
The causes for the incomplete dust bathing sequences are either in adequate substrate or social disturbances.
Cox and de Baere (2005) observed similar rates of short and incomplete dust bathes in both, deep litter boxes and on scratching mats without obvious reasons for the interruption. Feed as substrate does not contribute to remove lipids of the feathers, which is suggested a function of dust bathing (Scholz et al., 2011; 2014b). Sham dust bathing, however, also occurs independently of the lipid contents of the feathers (Norgaard-Nielsen and Vestergaard, 1981) and even in total absence of litter on wire floor (Bessei and Klinger, 1982; Lindberg and Nicol, 1997). There exist controversial opinions among scientists regarding welfare implications of substrate. While some authors consider dust bathing behavior without substrate as abnormal behavior, which does not fulfill the natural drive of the hens (Vestergard, 1980; Louton, 2014), others concluded that the performance of the behavior as such is important, regardless of the substrate ( Lindberg and Nicol, 1997; Widowski and Duncan, 2000). The relative importance of litter for dust bathing has been studied in experiments using different methods. While the birds make extensive use of litter, when it is freely available, they are not prepared to work hard to get access to litter (Dawkins, 1983; Laine et al. (2007). On the basis of such experiments it has been concluded that dust bathing behavior has a low “priority” (Petherick et al., 1993; Bubier 1996). This may be the reason why there is no social competition for the dustbathing area even under crowded conditions (Olssen and Keeling, 2003). Independently of the influence of litter on the behavior of the birds, regular distribution of wheat bran on the scratching mats of furnished cages has shown positive effects on mortality, body weight and feather scores of non-beak trimmed layers (Huneau-Salaün et al., 2014).
Problems related to the nest
According to the EU regulation 1 m² of nest area is required for 120 hens in deep litter systems. This corresponds to 83 cm² per bird. There is no EU regulation for the nest area in furnished cages. But in Germany a minimum the nest size per cage is 800 cm². This space can be shared by 10 hens. Nest area is not comprised in the figures of floor space. According to the EU regulation the nest floor should be constructed in a way that the hens are not in contact with wire mesh. Therefore the roll away wire floor is usually covered with different types of plastic material. One manufacturer provides a plastic coated wire mesh. This complies with the wording of the regulation. It is, however, not allowed in Germany. There exist plenty of choice experiments to elucidate the preference for different types of nests, positions within the house and characteristics of the nest floor.
The essential criterion for the hen to accept an area as nest is the enclosure and its accessibility (Rauch, 1995).
While nests in barns and aviaries are built in separate blocks, located on the slatted floor (integrated nests), or at the walls, the nest area in furnished cages is separated by metal walls or – in most cases – by plastic curtains. The acceptance of nests is relatively high in both furnished cages and non-cage systems. Independently of the nest type more than 90 percent of the eggs are laid in the nest (Wall and Tauson, 2013). The distribution of the hens can be highly unbalanced across the nest position. Higher nests and nest in an integrated position are usually preferred. This results in overcrowding in these sections and cause mortality through overheating or suffocating. The problems can be further aggravated when not sufficient nest space is provided. The occupation of the nest area also depends on the synchronization of oviposition within a flock and the average time of the birds spent in the nests. Icken et al. (2009) recorded the presence of hens in individual nests using transponder technique. The time of maximum nest occupation varied among different flocks from 2 to 5 hours, and the mean duration of stay in the nest from about 30 to 45 minutes. This corresponds with results of Sherwin and Nicol (1993) and Petherick et al. (1993). In some studies the duration of stay in the nest was shorter (25 min; Freire et al. (1998) or even longer than 1 hour (Cooper and Appleby, 1996). Regarding the high variability of nest use it may be advised to provide more than the minimum nest space laid down in the EU directive.
Nest area has to be provided additionally to the basic floor space allowance. Therefore the farmers not only have to invest in more nest area but also in increased the total house surface.
The risk of mortality through overcrowding in the nests is rather low in furnished cages, especially when plastic curtains are used. The hens may exit the nest at any place when too many birds try to lay their eggs at the same time. There is, however the risk of cloacal cannibalism when during oviposition the vent of the birds is visible outside the curtains and attracts the attention of cage mates. It is therefore advised to increase the nest area and to keep the gap between the curtains and the floor as small as possible (Anonymous, 2012).
Chickens have a strong motivation to rest and sleep on perches. The availability of perches has therefore been considered a basic behavior need.
The minimum perch space for layers housing systems in Europe is 15 cm per bird. There was, however, no difference in the percentage of hens perching whether the perch length per bird was higher (17 cm; Hergt et al, 2007) or lower (12 cm; Tauson, 1984). Similar to the nest area the perches are often not evenly occupied. Higher perches are usually preferred over lower ones. This can lead to extreme crowding on the upper tiers of aviaries (Abrahamsson and Tauson, 1993). The welfare aspects of perches not only concern resting behavior. Perches are considered to reduce aggression and feather pecking by allowing the birds to escape from aggressive or cannibalistic attacks of group mates. This has been confirmed by Donaldson and O´Connel (2012). Perches also increase bones strength, mainly of the wings (Sandilands et al., 2009). However the movement to and from aerial perches bears the risk of bone fractures. The furculum and the keel bones are mainly affected. The percentage of layers of none cage systems showing old bone fractures at the end of the laying period range from 50 to 80% (Wilkins et al., 2004; Freire et al., 2003; Scholz et al., 2008). The causes for bone breakage are manifold. Osteoporosis is considered the predisposing factor. In addition, inadequate position of perches, crowding in certain areas, low light intensity, poor flying ability and experience, and high body weight have been identified as risk factors by Sandilands et al. (2009). According to own observations there are frequent accidents in aviaries when the birds try to descent from higher tiers of aviaries in the morning. Raised platforms with integrated perches and ladders in between the tiers may reduce the risk of accidents. However, integrated perches are not generally accepted as ”perches”. Since chickens prefer higher perches it is assumed that they do not feel save on the lower ones. Hence “aerial” perches only are considered to meet the natural needs of the birds by some authors. There is, however, no generally accepted minimum height for perches. Some definitions of perches require that the perch must not be fitted on the slats, or that the perch should be positioned in a height that other birds can pass underneath, or that the perching birds may not be reached and disturbed by birds walking on the floor. According to tests of Faure and Jones (1982a,b) laying hens perceive surfaces raised 5 cm above the floor as perch, regardless of their characteristics. This shows that from the bird´s side even integrated perches may satisfy their need of perching. The availability of perches may reduce the risk to be cannibalized (Gunnarsson et al., et al., 1999; Pötzsche et al., 2001). It is, however, known that targets of feather pecking do not try to escape and often tolerate continuous and severe feather pecks and cannibalistic pecks. This is in contrast to aggressive attacks. Therefore perches may be useful to avoid aggressive pecks but not feather pecks. Perches may even lead to more damages when they are located in a way with birds presenting vulnerable body part to feather peckers (Moinard et al., 1998). Pickel et al. (2010) could show that most of the body weight rests on the keel bone while the hens are sitting on the perch, and the permanent pressure is most likely the cause of the deformation. Newly developed perches with a soft surface have shown to reduce keel bone deformation and improve the footing characteristics (Scholz et al., 2014).
Improved designs of perches not only reduce keel bone damages through high pressure during resting, but also prevent bone breakage through save navigation.
Free-range is the considered the most welfare friendly management system where the birds enjoy more freedom to move and a wide variety of environmental stimuli. Most consumers perceive free range as adequate and natural environment for chickens. Problems arise when large groups of hens are kept under free-range conditions. Domestic chickens tend to keep close contacts with their pen. The mean distance of chickens kept from the stable when their movement was not restricted by fences was 50 m, and in some cases up to 300 m (Engelmann, 1948). These results were confirmed by recent studies. 60 percent of the birds remained in a distance of 50 m from the stable, and only a few birds moved to a distance of 250 m. The percentage of birds observed in the free-range was in the range of 30 to 36 (Harlander-Matauschek et al., 2001). The use of free-range declined with increasing flock size but not with reduced size of the openings (Harlander-Matauschek et al, 2001). There was a high variation of the use of free range of individual birds. The mean time spent in the free range was about 4 hours per day. Rauch et al. (1999) reported a negative relationship between the number of visits to the free range and the duration of visits. The majority of the birds spent a large number of short visits (less than 5 minutes), while a few birds spend up to 4 hours continuously in the free range. The concentration of the visits on the area nearby the openings leads to rapid deterioration of the vegetation and accumulation of nutrients in the soil and ground water. Therefore the establishment of free-range systems is not permitted in many areas. Various attempts have been made to ensure a more regular use of the available space through different types of natural or artificial shelter, tries, bushes china grass, huts, etc. These measures increased to some extend the distance of the birds from the poultry house, but not significantly the percentage of birds using the free range (Harlander-Matauschek et al., 2001). The establishment of a winter garden as transition between indoor and outdoor conditions is being used as complementary element in barns, aviaries and free-range systems. The birds may use the roofed area adjacent to the stable under adverse climatic conditions. This protects the vegetation of the free-range and, at the same time, gives the birds the opportunity to move, scratch and dust bath in the open air. The winter garden, however, is recognized as part of the indoor surface and not as free range. Therefore the birds have to be given access to the range at any time during the light period and the area close to the outlets is becoming muddy during rainy days. The birds carry dirt inside the buildings and the nests. Since the free range has to be opened as soon as the light is switched on, there is also a risk that eggs are laid in the range area. Another problem of the free-range regulation is the prohibition to use the free-range for other purposes. This prevents planting maize or other cultures, which remove the nutrients excreted by the birds and at the same time provides shelter against predators.
The establishment of mobile free-range systems is becoming popular for small scale layer farms. There exist a wide range of commercial mobile layer houses. The constraints are supply of water and electricity, removal of manure, high labor costs and low production rates.