ESR blog
Introduction
Major policy changes in Europe, North America and recently New Zealand to improve animal welfare led to an increased number of chickens kept in alternative housing systems instead of cages. We asked consumers through a social media poll to give their opinion on what is considered most important when choosing a chicken product based on the production system. Based on the results (30 votes), consumers prefer products from chickens that have been raised in a production system where their health is prioritized. The second priority of the consumers is product safety. Some consumers also put emphasis on the chickens’ ability to behave naturally in the production system used.
In this blog, we evaluate how the housing systems may impact the health, product safety, and behavior of chickens.
Health
When evaluating free-range poultry systems, increased contact with pathogens should be taken into account. In a free-range system the environment is not controlled or only partially controlled, which makes transmission of diseases more likely. McMullin (2022) reviewed the prevalence and severity of infectious diseases across the different poultry housing systems. While higher risk for viruses like New-Castle and avian influenza can be expected, the range of biosecurity measures will make the difference, not the fact that the chickens have an outdoor area. Endemic bacterial infections with E. coli, Gallibacterium, erysipelas and others were found to be higher in free-range systems and lower in cages. Another notable example would be soil-transmitted helminths which are a re-emerging infection across the countries that have adopted the free-range system (Sherwin et al. 2013). It can be argued that the co-existence of pathogens with chickens is a natural phenomenon and that is how things exist in the wild. For example, chickens in free-range systems do not always show clinical symptoms (Sharma et al. 2018) or a reduction in egg production to infections with Ascarids (Sherwin et al. 2013), leading to the assumption that the birds cope just fine. On the other hand, it is difficult to ascertain if birds infected with pathogens are under any sort of pain especially when there are no clear clinical signs. Shimmura et al. (2010) however showed that birds raised in a free-range system had the lowest score for freedom of pain, diseases and injury compared to cage system, although immune response was higher in birds kept in a free-range production system.
Furthermore, the type of birds in each production system influences their adaptability as well as the resilience (Castellini et al. 2016). Slow-growing breeds and high producing breeds of birds are different in their anatomy and genetics. Commercial birds have been selected for high productivity over decades, implying that they have become less resilient to infections given the negative correlation between health and productivity. The more energy and resources are used for production, the less is available for fighting pathogens. Conflicting with this, however, lower worm burden and shedding of eggs was found in commercial birds (Lohmann brown) compared to Danish Landrace (Permin and Ranvig 2001), but this study is now over 20 years old, and the genotype has changed a lot. The increased exposure to pathogens is not the only thing that threatens the health of birds in a free-range system. The increased exposure to pathogens is not the only thing that threatens the health of birds in a free-range system. For instance, also cases of increased cannibalism (e.g., feather pecking) and of nutrient deficiency have been reported in free-ranged birds.
Food Safety
Food safety is another important aspect of consideration in the evaluation of poultry housing systems and, as shown in the result of our poll, is important to consumers. Studies have found that the prevalence of certain zoonotic infections is considerably affected by the production system. The most common zoonotic pathogens in poultry are CampylobacterA common bacteria present in poultry gut causing little to no clinical symptoms. and Salmonella and are known to be transmitted to humans mainly via poultry meat and eggs (Iannette et al. 2020). According to the “European Union One Health 2021 Zoonoses Report in 2021”, a total of 127,840 and 60,050 human cases related to campylobacteriosis and salmonellosis, respectively, were observed in the European Union (EFSA 2022). These pathogens will also cause antigen stressStress that occurs due to induction of immune response caused by complex molecules present in the wa… to the birds, thereby compromising their welfare (CampylobacterA common bacteria present in poultry gut causing little to no clinical symptoms.: Awad et al., 2017 and Salmonella: Ijas et al., 2021). Therefore, controlling these pathogens is important in terms of product safety and animal welfare in poultry production. However, previous studies reported contrasting results related to the prevalence of CampylobacterA common bacteria present in poultry gut causing little to no clinical symptoms. contamination of broilerChickens kept for meat production. Fast growing breeds can reach a weight of over 2 kg at 5 weeks of… meat from alternative farming systems vs. conventional farming systems. Heuer et al. (2001) and Rosenquist et al. (2013) reported that CampylobacterA common bacteria present in poultry gut causing little to no clinical symptoms. contamination in broilerChickens kept for meat production. Fast growing breeds can reach a weight of over 2 kg at 5 weeks of… meat was higher in organic farms than that of conventional farms while Lücke (2017) reported that although the prevalence was higher in live birds of free-range systems, CampylobacterA common bacteria present in poultry gut causing little to no clinical symptoms. contamination in meat was similar to that of the conventional farms. Interestingly, much research conducted in Europe indicated that Salmonella incidences in free-range broilersChickens kept for meat production. Fast growing breeds can reach a weight of over 2 kg at 5 weeks of… and layers are lower than that of conventional farms as reviewed by Holt (2021). However, this author claims that the free-range farms are relatively new and the accumulation of Salmonella in soil in free-range system can occur over time which can possibly give rise to a change in results in future. As Sosnowski and Osek (2021) reviewed, prevalence of Shiga toxin producing E. coli, Staphylococcus aureus and Listeria monocytogenes pathogens in alternative farming systems also were lower than or equal to that of conventional farms. However, the breeds of the poultry, housing facilities (access to wild birds and animals) and management (deworming, prophylaxis etc.) might be different in the farms used among the above experiments. Therefore, with these contrasting results, it is difficult to conclude about the microbial safety of the products from alternative systems compared to conventional production systems.
Also in egg production, bacteria like E. coli, CampylobacterA common bacteria present in poultry gut causing little to no clinical symptoms. sp. and especially Salmonella enterica are a concern. In free range systems, the birds have closer contact to wildlife, which increases the risk of introduction of pathogens (Holt et al. 2021). However, studies did not clearly show a higher prevalence of foodborne pathogens in alternative housing systems compared to cages: a higher prevalence of Salmonella sp. in cage systems was reported by Methner et al. (2006), while De Vylder et al. (2011) found a trend for higher horizontal transmission of Salmonella enterica serovar Enteritidis between hens housed in an aviary system compared to a cage and a floor system. A higher prevalence of CampylobacterA common bacteria present in poultry gut causing little to no clinical symptoms. sp. was reported for laying hens from alternative housing systems, but the difference was not statistically significant (Rama et al. 2018). Therefore, there is presently no clear evidence for a higher risk of food-borne pathogens in alternative housing systems for laying hens.
However, when the birds have access to the outdoors, it is obvious that they will be exposed to other uncontrolled environmental factors such as ambient temperature fluctuations, predators, contaminants from wild animals as well as contaminants in soil. As reviewed by Holt (2021), many studies have demonstrated that the dioxin (toxic industrial contaminants from soil) content in eggs from free range chickens are higher than that of conventional farms. Therefore, in terms of the safety of products, multiple factors must be considered in alternative farming systems. Strategies like maintaining strict biosecurity even in outdoor environment, proper maintenance of the housing system to avoid unnecessary predation and mortality, prophylaxis and early microbiome reprograming can be identified as strategies to overcome these adverse effects related to food safety from the alternative production systems. Thus, more applied research is necessary in future to ensure the product safety and welfare of the birds in these systems.
Behaviour
The freedom to follow the natural and species-specific behavior is an important aspect of animal welfare (Fraser 2008). Key behavior elements for a laying hen include grooming (preening, dust bathing, stretching), perching, foraging, and nesting. Most of these are not possible in a conventional cage system, which is not in use in the EU anymore, and extremely limited in an enriched cage system. The stimuli provided in an enriched cage are few and do not elicit a lot of foraging and exploring activity. An aviary provides more stimuli, while the free-range systems provide the highest amount and diversity of stimuli, enabling the hens to forage and explore. The natural light containing an UV portion allows for natural perception of the surroundings. Often though, the surroundings of the stable are barren and deprived of stimuli due to intensive use by scratching and pecking. To increase the use of the whole outdoor area, enrichment like bushes, trees or artificial covers must be provided, which make the hens feel more secure (Knierim et al. 2006). Roosters can also provide security to the hens. Furthermore, the hens can seek fresh air to escape high dust and ammonia levels in the stable, which is not possible in an aviary, where dust and ammonia levels can be high due to the activity of the hens and the lack of separation from their excretions (Knierim et al. 2006). More fearful and distressed behavior has been observed in caged housing while hens in outdoor systems showed more comfort behavior and were less fearful (Nenadovic et al. 2022). Furthermore, a better plumage has been observed in hens with outdoor access indicating less injurious behavior and the possibility to escape antagonistic behavior (Rodenburg et al. 2013, Sosnówka-Czajka et al. 2021).
Perching is possible to a limited degree in enriched cages, but the positioning in a confined environment can lead to injuries due to collision and cloacal pecking (Hartcher and Jones 2017). The multiple levels in an aviary or free-range system provide ample opportunity to perch, which is especially used at night (Fraser et al. 2013, Sosnówka-Czajka et al. 2021). The opportunity to perch increases the hens’ feeling of security and provides exercise (Donaldson and O’Connell 2012, Yan et al. 2014). It is important that pullets are acquainted with the use of multiple levels and perching structures to avoid collisions, falling from perches, and resulting bone fractures (Hartcher and Jones 2017).
In an enriched cage, the requirement for dust bathing is usually addressed by providing feed on a plastic mat, which is soon exhausted (Hartcher and Jones 2017). Additionally, dominant hens can deny access to more submissive hens. An aviary and free-range systems with provided litter material allow for dust bathing behavior, but management must ensure that the material is kept dry and lose and maintain the outdoor areas accordingly.
Cage-free aviaries and free-range systems come with new challenges. The large groups of hens in an aviary system can increase antagonistic behavior like feather pecking. This behavior has been shown to originate from individual birds and can spread more easily through larger groups (Hartcher and Jones 2017). The enrichment of the diet by natural foraging can lead to nutrient imbalances which in turn can exacerbate feather pecking. Mortality due to predation is higher in outdoor systems and not all hens use the outdoor facilities (Knierim et al. 2006). Furthermore, a higher prevalence of red mites (Dermanysses gallinae) was found in outdoor housing systems, which can increase stress and lead to more antagonistic behavior (Sosnówka-Czajka et al. 2021). This must be alleviated by proper management.
Broiler chickensChickens kept for meat production. Fast growing breeds can reach a weight of over 2 kg at 5 weeks of… are normally reared indoors on the floor and free-range systems are not so widespread. Additionally, slower-growing breeds are often used for free-range and organic systems, making it more difficult to compare the behavior of the birds in different housing systems. In fast-growing broilersChickens kept for meat production. Fast growing breeds can reach a weight of over 2 kg at 5 weeks of…, it was observed that the birds did not make much use of extra space due to the weight-related walking impairment at a certain age (Weeks et al. 1994), though at the beginning, the chickens were more active in free-range systems (Weeks et al. 1994, Zupan et al. 2005). Slower-growing breeds were observed to readily use additional space and enrichment objects like perches up to the end of the production cycle, but similar issues concerning range use as in layers were found (Kanstrup et al. 2021). Another study concluded that slow-growing breeds are more suitable for free-range systems based on better welfare parameters. However, no significant differences for the housing systems were found (Abdourhamane and Petek 2022).
Finally, alternative housing systems can increase welfare and the opportunity for laying hens to show their natural behavior, but more maintenance and biosecurity measures are needed to achieve this on a long-term basis and minimize losses while maximizing production. In broiler chickensChickens kept for meat production. Fast growing breeds can reach a weight of over 2 kg at 5 weeks of…, slow-growing breeds should be used in free-range systems. Fast-growing breeds are restricted in their use of the enriched environment due to their anatomy.
Conclusion
In conclusion, while alternative housing systems has perceived benefit for chicken welfare through expression of natural behaviour one must also not neglect the potential detrimental effects it poses to chickens. Perhaps it would be favourable to utilize breeds (e.g., dual purpose breeds) that are adapted to the outdoor/free-range production system. For broilerChickens kept for meat production. Fast growing breeds can reach a weight of over 2 kg at 5 weeks of… production, slow-growing breeds should be used in free-range systems. Fast-growing breeds are restricted in their use of the enriched environment due to their impaired ability to move. Moreover,innovative strategies are needed to achieve better welfare on a long-term basis and minimize losses while maximizing production. Regardless of the housing system, maintaining a strict biosecurity system is the key to address food safety concerns.
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