July 29, 2026

expert reaction to environmental impact of welfare-driven policy changes in UK egg production

A study published in Royal Society Open Science looks at the environmental impact of welfare-driven changes in UK egg production. 

On environmental impact:

Dr Laura Cardenas, Atmospheric Chemist specialising in farming footprints at Rothamsted Research, said:

“The study concludes that although animal welfare improves when changing ‘business as usual’ for non-cage, free range and organic management, their environmental burden increases. This is based on 3 animal welfare indicators and mainly 3 environmental metrics – greenhouse gas emissions, acidification and eutrophication.

“The authors have assessed the global warming potential (GWP) of the different scenarios, expressing the emissions in CO2eq per kg of eggs. I would question these units, as GWP is an IPCC definition to describe an index that expresses the cumulative radiative forcing between the present and a future time horizon caused by a unit mass of gas emitted now, expressed relative to that of CO2. The acidification potential refers to sulphur only and eutrophication to phosphorus only. If other compounds were included in the calculations, it would have been good to have this explained.

“The main reason why the cage-free and organic systems are environmentally worse is that these systems require more animals to achieve the same level of production. Emissions pretty much only arise from the feed produced (elsewhere) and the manure the animals generate, as more animals are required in the more extensive systems – this explains the difference. So in reality the difference between systems is due to animal numbers, not the system itself.”

Dr Adrian Williams, Visiting Fellow in Agri-Environmental Systems at Cranfield University, said:

“The main findings are basically consistent with earlier studies that compared egg production systems using Life Cycle Assessment (LCA) and are thus not a big surprise.

“The contrasts between caged and any free-range system would be amplified had the authors include more detailed work on mortality rates by the Bristol Vet School¹. Their use of mortality rates as a welfare indicator tells an important story in a pointed way, but omits the ‘quality of life’ aspect, which is challenging to quantify in Life Cycle Assessment. The lower overall productivity of organically managed egg production is the reason behind the larger negative environmental impacts that occur compare with non-organic counterparts. This contrasts with most other aspects of organically managed farming.

“Including indicators about non-renewable resource use, toxicity or biodiversity may well have balanced the overall poor ratings of organically managed egg production somewhat, but this would still not stop the higher emissions and land use that this paper highlights.”

¹ doi:10.1371/journal.pone.0146394

Prof Dominic Moran, Professor of Agricultural and Resource Economics, Roslin Institute, University of Edinburgh, said:

“The paper is a reasonably robust use of modelling to illustrate a policy dilemma: higher welfare won’t always come with environmental improvements, especially in terms of emission reductions. 

“There are trade-offs that both policymakers and consumers need to face when outcomes – such as animal welfare and environmental benefit – compete with each other.  It forces us to consider which outcomes do we most value and are we willing to pay for.This study shows that it’s difficult to have free range hens without increasing harmful emissions – and we need to be honest with the public about that.”

On animal welfare:

Prof Ilias Kyriazakis, Professor of Animal and Veterinary Science at Queen’s University Belfast, said:

“The paper is methodologically flawed. It relies on our data from 2010 to construct scenarios intended to represent national conditions in 2023, without adequately accounting for the substantial changes that have occurred over that period. More concerning is the authors’ apparent disregard for the uncertainty associated with the underlying data. Ignoring these uncertainties introduces bias into the analysis and leads to conclusions that systematically favour furnished cage systems, which dominate the business-as-usual scenario.

“The paper utilises our data which was generated between 2009-10, so the data is at least 17 years old. Although it is the most comprehensive dataset ever generated in the UK, the Industry moves at a fast pace. For example in our 2012 we found reductions in the environmental impacts of hen systems between 2006 and 2012 which were ascribed to management adjustments.

“There is no doubt that the cage systems will always have lower environmental impact compared to the other systems. This is based on feed efficiency as birds in cage systems use less feed to produce the same amount of eggs. However, the efficiency differences between the other three systems is less clear, which is inconsistent with the authors assertions.

“The authors give no detail about the methods of manure management and accounting. For the analysis of the same data we used manure related data published from Defra-funded work in 2006. However, since then Defra has published updated values for emission factors across different laying systems. By disregarding these updated values, the authors are likely to have overestimated some of the impacts of the alternative systems (eutrophication and acidification potentials especially).

“The paper uses bird mortality as an iceberg mortality indicator. I understand why they are using our mortality data for their calculations, having used our data for feed utilisation etc. However, it is highly likely that the mortality figures will have improved, especially amongst free range and organic birds.

“In summary, the paper uses out of date data for their calculations. Their calculations do not bring to light new information of importance to the public and policy makers. They disregard errors associated with our data, so their claims become spectacular when they are upscaled. Having said all that, I fully agree with the conclusion made in the paper: ‘the need to integrate environmental and welfare outcomes when guiding future transitions toward non-cage egg production’.”

Prof Christine Nicol, Professor of Animal Welfare at the Royal Veterinary College, said:

“The mortality data and the systems described by the authors are more than 10 years out of date.  Since 2012, cage-free hen systems have improved and producers have gained new management skills – mortality in indoor non-cage systems is now on a par with that seen in cages¹.  In addition, non-cage systems provide hens with welfare benefits not considered in this study, such as behavioural freedom and choice.

“Hen mortality is not the only way of measuring welfare, although I agree with the authors that it’s an important one as most deaths are preceded by a period of suffering.  But I am unconvinced that the mortality figures in this study represent current barn and free-range systems which have evolved and improved considerably.  Many independent studies actually report low mortality in modern indoor barn/aviary systems.  Mortality in free-range and organic systems can be more variable.  However, mortality in all types of non-cage system has reduced over time as farmers learn how to manage these systems.

“The key to improving welfare and environmental aspects together is to monitor indicators such as mortality and provide help and advice to farmers who are not managing so well. We must not return to fully restrictive systems, and the recent EU Livestock strategy (July 2026) will indeed move to phase out the use of cages.”

¹ https://pubmed.ncbi.nlm.nih.gov/33542280/

Prof Tim Morris, Professor of Laboratory Animal Welfare and Science at the University of Nottingham, said:

“Studies suggesting the welfare of caged birds is worse than free range birds have driven changes in animal welfare policies and egg production systems in the UK, but are there wider impacts?  

“The detailed whole-lifecycle approach used in this study helps compare the wider environmental impacts between different egg production systems but the actual animal welfare impacts between each production system are not as clear because the study did not include a similar detailed whole lifecycle assessment of the quality of life of the birds. This makes it difficult to fully measure any environment costs or benefits of these policy changes against any animal welfare benefits or costs.”

‘The environmental cost of welfare-driven policy changes in UK egg production’ by Oliver Martinic et al.was published in Royal Society Open Science at 00.05 UK time Wednesday 29 July 2026.

DOI: https://doi.org/10.1098/rsos.251830

Declared interests

Ilias Kyriazakis: “I am the senior author of the papers used in this analysis. I am also a member of the Sustainability Committee  of the World Egg Organisation. ”

Dominic Moran: “no interests to declare.”

Laura Cardenas: “no conflicts”

Tim Morris: “This was my public register a while back, many have not lapsed, and no relevant new ones: http://data.defra.gov.uk/AnimalWelfare/ahwbe_interests_072015.pdf”

Adrian Wlliams: “No interests”

Christine Nicol:

For all other experts, no reply to our request for DOIs was received.