Surprising Reason Cage-Free Eggs May Be Worse for the Planet

Animal welfare advocates have long pushed for a world where egg-laying hens roam freely rather than spend their lives crammed into cages. That goal sounds straightforward. But a new study finds that the environmental trade-offs involved are substantial and often run counter to what welfare improvements would suggest.

Research published in Royal Society Open Science models what would happen if UK egg production shifted away from cage-based systems and toward free-range or barn setups. Those results point to higher greenhouse gas emissions, worse air and water pollution, and greater land use. Under the study’s modeled scenarios, which hold total egg output constant, a cage-free transition would also mean more hens die on farms each year. Authors of the paper argue that these environmental and welfare dimensions should be weighed together in future policy decisions, rather than treated separately.

Eggs are one of the most widely consumed animal products on Earth, with global production quadrupling over the past 50 years. In the UK, public pressure and market trends have pushed egg producers steadily away from cage systems since 2020, with free-range eggs gaining a growing share of supermarket shelves. This study models the environmental and welfare consequences of different production scenarios at a national scale, holding total egg output constant across each.

How the Cage-Free Study Was Conducted

Researchers modeled eight different scenarios for how the UK could produce the same amount of eggs it produced in 2022, when the national laying hen population was estimated at 40.44 million birds. Each scenario kept total egg output constant but changed the mix of farm types used to produce those eggs.

Farm types included furnished cages (the only cage type currently legal in the UK), barn systems where hens move freely indoors but have no outdoor access, non-organic free-range systems, organic free-range systems, and battery cages (banned in the UK but still used globally). One scenario reflected the current mixed production system, which includes roughly 26% furnished cage, 7% barn, 63% non-organic free-range, and 4% organic free-range production. Other scenarios tested what would happen if cages were eliminated entirely in favor of free-range or barn systems, or if the entire national supply came from just one farm type.

To measure environmental impact, the researchers tracked pollution and resource use across the entire production process, from growing chicken feed to managing manure on farms. Four environmental measures were calculated: greenhouse gas emissions, water-polluting nutrients, air-polluting gases linked to acid rain, and land use. Welfare was tracked using three indicators: the total number of hens needed to meet production targets, the percentage of hens that die during their laying period, and the total number of hens slaughtered at the end of their productive lives.

What the Numbers Show About Cage-Free Eggs

On a per-kilogram-of-eggs basis, cage systems consistently had smaller environmental footprints. Furnished cages had the lowest scores across all four environmental measures. Organic free-range systems had the highest greenhouse gas emissions, the greatest demand for land, and the highest water pollution scores. Barn systems ranked worst for air-polluting gases, largely because of the energy they consume.

Scaling these numbers up to the national level made the contrasts starker. Under the current mixed production system, UK egg farming generates an estimated 1,439 kilotonnes of carbon dioxide equivalent per year. Shifting cage production to free-range would raise that figure by about 5.84%, while shifting to barns would push it up by about 13.55%. A full national transition to organic free-range production would increase emissions by more than 60%, to an estimated 2,316 kilotonnes. By contrast, a fully furnished-cage system would cut national emissions by nearly 18%.

On the welfare side, the results upend some common assumptions. Free-range and organic systems are widely perceived as more humane, and for individual hens, there are real benefits in terms of space and the ability to engage in natural behaviors. But those systems are also less efficient: hens in cage-free environments produce fewer eggs per bird, which means more birds are needed to keep shelves stocked.

Mortality rates varied considerably across systems. In furnished cages, approximately 2.5% of hens die during their laying period. In free-range systems, that figure rises to 7%, and in organic free-range systems it climbs to 8%. Compared to the current mixed production baseline, a full shift to non-organic free-range production would result in an estimated 440,000 additional hens dying on farms each year. A full shift to organic free-range would add roughly 1 million additional farm deaths annually.

Why Cage-Free Egg Production Costs the Environment More

Feed production was the single biggest driver of environmental impact across all systems. Free-range hens consume more feed per egg produced than caged hens, which ripples outward into higher emissions, more land devoted to growing crops, and greater nutrient runoff into waterways. Even the outdoor space that free-range hens enjoy contributes to higher emissions because their manure is spread over larger areas.

Researchers noted that improving feed choices or production efficiency within any given system could reduce its environmental footprint, regardless of which system a country chooses. Cage-free systems that achieve higher feed conversion ratios or lower mortality rates would outperform the averages used in this analysis.

One limitation the authors acknowledge is that the study modeled only scenarios in which total egg production remained constant. Reducing how many eggs people eat, which some dietary guidelines already recommend, could improve both environmental and welfare outcomes at once.

Campaigns to ban cage systems for laying hens have gained traction across Europe and beyond, driven largely by genuine concern for animal suffering. That concern is valid, and the researchers are not arguing against welfare reforms. But this study makes a pointed case that environmental costs belong in the conversation.

Within the scenarios modeled, removing cages from UK egg production, a shift that current market trends are already driving, is associated with a measurable increase in greenhouse gas emissions, land use, and the number of hens that die on farms each year. Authors of the paper suggest that policymakers seeking better outcomes for both animals and the environment may need to think carefully about how non-cage systems are designed and managed, not just whether cages exist at all.

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