Using UK data, the study compared several possible scenarios for the egg industry, including shifts to barn, free-range and organic systems, while keeping egg output constant. The authors find that although cage-free systems may align more closely with public concern for hen welfare, they may also require larger hen populations and could increase environmental pressures. Shifting to an entirely free-range and organic method of egg production from a business-as-usual scenario, for example, would raise emissions by 60% while almost doubling land occupation. These results highlight the need to integrate environmental outcomes when guiding future transitions toward non-cage egg production, the authors say.
“Our research highlights the importance of considering animal welfare, environmental impact and food production together when shaping the future of egg farming,” says author Dr Harriet Bartlett , Senior Research Associate at the Smith School of Enterprise and the Environment, University of Oxford. “Being aware of these tricky trade-offs will help us make better decisions for the environment and animal welfare in the future,” she adds.
The global food supply chain creates 26% of human-caused greenhouse gas emissions and is responsible for 78% of eutrophication (excess nutrient enrichment of water), and 32% of terrestrial acidification (soil damage). Global production of eggs is a key driver of these impacts, having quadrupled over the past 50 years.
Meanwhile, advocacy for a wholesale transition away from cage-based husbandry systems has increased. “While this movement is driven by important concerns around farm animal welfare, differences in production performance among husbandry systems could lead to unintended outcomes,” says lead author Oliver Martinic, an independent researcher based in Croatia.
“This is not to say concerns around eggs from caged chickens can or should be dismissed or that we should return to restrictive caged systems. But we want farms and consumers to be aware of all the potential impacts when it comes to the methods by which we produce our food,” says Dr Bartlett. “By taking a broader view, we can find the best ways to balance these trade-offs as we pursue a more sustainable global food system.”
The authors also found a significant rise in mortality for 100% free-range and organic systems. However, they acknowledge the data used in the study were collected between 2009-10, and progress has been made since then. “This is an important limitation, and we are transparent about it in the paper. However, these data remain the most comprehensive available for laying-hen production systems in the UK,” says Martinic.
Q&A
Q: Are you saying we should return to caged-only chicken farming?
A: No. Our research highlights important trade-offs between different types of egg production, but it is not calling for a return to caged farming. We recognise that the transition towards cage-free production is important for improving animal welfare. However, our findings also suggest that transitioning to cage-free systems without also improving factors such as mortality and feed efficiency is likely to increase environmental impacts. The challenge is therefore to develop production systems that combine high standards of animal welfare with improved animal performance and lower environmental impacts.
Q: The paper utilises data which was generated between 2009-10. Why did you use this data for your study?
A: We acknowledge that the data used in this study were collected between 2009 and 2010 and therefore do not capture more recent developments in laying-hen production. This is an important limitation, and we are transparent about it in the paper. However, these data remain the most comprehensive dataset available for laying-hen production systems in the UK. While more recent studies exist, they typically focus on only a subset of production systems (for example, indoor only), making direct comparisons across all housing systems difficult. Combining data from different sources would also introduce methodological inconsistencies that could reduce the robustness of the comparisons.
Generating an equivalent, up-to-date dataset covering all production systems is challenging. More recent data are difficult to obtain, particularly because data collection has been affected by challenges such as avian influenza outbreaks and difficulties in obtaining representative data from barn and organic production systems. Although production practices have undoubtedly evolved since 2010, we consider this dataset to remain the best available resource for population-level analysis of the environmental impacts and trade-offs associated with different laying-hen production systems.
Q: How did you account for manure management in the study?
A: We calculated excreta production based on feed consumption, while the environmental impacts associated with manure management were estimated using IPCC methodology (2019). Emissions arising from manure management were therefore included in our assessment. We assumed that manure was routinely removed from housing facilities and subsequently applied periodically to cropland or pasture. Other post-farm processes were outside the system boundaries of our assessment and were therefore not considered.
Q: Why did you use mortality as an indicator for hen welfare?
A: We agree that mortality is only one dimension of animal welfare and does not necessarily capture other aspects such as behaviour or affective state. However, mortality is a meaningful population-level welfare indicator because it reflects the loss of animals within the production system and can be directly incorporated into environmental assessments, as animals that die have consumed resources without contributing to production.
We acknowledge that mortality rates may have changed over time. Nevertheless, mortality remains one of the few welfare indicators that can be consistently quantified and compared across production systems at a national scale. We hope this study provides a framework for future work that integrates more recent welfare data and a broader range of welfare indicators alongside environmental outcomes.
Q: What should consumers take away from this research?
A: Consumers should recognise that there are important trade-offs between animal welfare and environmental sustainability in egg production. No production system currently performs best across all welfare and environmental measures. Future progress will require improvements in animal performance and resource efficiency while maintaining or enhancing animal welfare. We believe that the most sustainable approach is to consider these factors together rather than focusing on a single indicator.
Q: Why does free-range and organic free-range egg production lead to higher mortality in chickens? And does this mean their quality of life is lower?
A: There are multiple reasons why mortality can be higher in free-range and organic systems, including greater exposure to disease, predation, injuries, and feather pecking.
However, mortality is only one aspect of animal welfare, and is not a complete measure of quality of life. Welfare is multidimensional and includes physical health, behaviour and emotional well-being. Nevertheless, mortality is an important "iceberg" indicator of welfare, as a death on farm is a clear welfare failure and often reflects underlying health, management or environmental challenges. Balancing lower mortality against other welfare outcomes, such as greater behavioural freedom, is a complex ethical question: if animals experience better opportunities for natural behaviour in a free-range system but mortality is higher, how should these different welfare outcomes be balanced? Conversely, if caged systems have lower mortality and higher feed efficiency, fewer birds may be required to produce the same quantity of eggs. The overall implications therefore depend on the perspective and the indicators considered.
Q: Why do caged chickens produce fewer emissions?
A: The lower environmental impacts associated with caged systems are primarily related to better animal performance and higher feed efficiency. Birds in caged systems generally consume less feed while producing the same quantity of eggs compared with birds in many cage-free systems. Because feed production is a major contributor to the environmental footprint of egg production, using less feed reduces the inputs required to produce eggs and therefore lowers associated emissions.
Q: Why do organic free-range farms create the most emissions and pollution, and what could be done to address this?
A: The long-term goal should be to reduce the environmental impacts of all production systems while maintaining or improving animal welfare. Achieving this will require improvements across several areas, including breeding, nutrition, feed production and farm management.
Organic free-range systems generally have higher environmental impacts because they tend to have lower productivity, higher feed requirements per egg produced, and lower crop yields for organic feed production. Together, these factors increase the land, feed and other resources required to produce the same quantity of eggs.
Reducing these impacts will require continued improvements in genetics, nutrition, feed production and farm management. The long-term goal should be to develop cage-free systems that combine high standards of animal welfare with improved production efficiency and lower environmental impacts.
Notes to editors
Once the embargo period ends, the study will be published here: https://doi.org/10.1098/rsos.251830
Please include this link in your reporting.
Funding: No funding has been received for this article.
Conflict of interest declaration. Margaret Hegwood undertook this research as part of her doctoral studies at the University of Colorado Boulder. All work was completed independently of her employment at The Centre for Feed Innovation. The other authors do not have a competing interest.
About Dr Harriet Bartlett
Harriet is an interdisciplinary scientist working on figuring out and incentivising the best ways to farm for people, the planet and the animals we farm. Her background is in preclinical veterinary medicine, which she studied at the University of Cambridge. She then worked at CSIRO, Brisbane on climate mitigation in red meat systems. Her PhD focused on comparing the carbon footprint, biodiversity impacts, antimicrobial use and animal welfare of a broad range of UK and Brazilian pig production systems - from intensive through to organic systems. She identified the types of farms that best limit negative externalities. Her work has been featured in the Guardian, BBC Farming today and she presented it at New Scientist Live.
About Oliver Martinić
Oliver Martinić holds a PhD in Animal and Food Science from the University of Padova, Italy (2022–2025). He is an interdisciplinary independent researcher based in Croatia, with research interests in sustainable food production, with a particular focus on animal production and welfare. In his research, he investigates the trade-offs between environmental impacts and animal welfare across different studies involving chickens and beef cattle. Martinić was a visiting PhD researcher at the Smith School and the Oxford Martin School, where he spent six months under the supervision of Harriet Bartlett and collaborated with the Hestia team.
Royal Society Open Science
Computational simulation/modeling
Not applicable
The environmental cost of welfare-driven policy changes in UK egg production
29-Jul-2026
Margaret Hegwood undertook this research as part of her doctoral studies at the University of Colorado Boulder. All work was completed independently of her employment at The Centre for Feed Innovation. The other authors do not have a competing interest.