Efforts to improve the welfare of chickens farmed for meat (commonly known as broilers) often focus on two strategies: reducing how many birds are kept in a given space and switching to slower-growing breeds. These changes can lead to significant welfare improvements, but they may also reduce production efficiency — raising concerns about higher greenhouse gas (GHG) emissions.

Although chicken is often seen as a lower-emissions meat, conventional systems raise fast-growing birds in crowded conditions, leading to serious health and behavioral issues. As interest grows in higher-welfare systems, this research investigates the environmental trade-offs that might come with them, using broiler production in Sweden as a case study.

The study examined how three higher-welfare scenarios affect both animal welfare and GHG emissions compared to a conventional broiler system:

1. Reducing stocking density
2. Switching to slower-growing broiler chicken hybrids
3. Combining both interventions

The goal was to understand the size of potential trade-offs and whether some approaches could offer major welfare gains without major environmental costs.

The researchers conducted a systematized review of 14 studies that assessed the impact of reduced growth rates and stocking densities on chicken welfare, using indicators such as lameness, foot-pad dermatitis, and mortality. They then modeled the GHG emissions of each production system using a life-cycle assessment, incorporating feed, housing, manure, transport, and parent breeder birds. These calculations were based on the slower-growing hybrids taking 49 days (Ranger Classic breed) and 56 days (Hubbard JA757 breed) to reach slaughter weight compared to 35 days for the fast-growing Ross 308 breed.

The study found that slower-growing broiler chickens showed a 37% average improvement in overall welfare, especially in leg health and mortality. Reducing stocking densities improved overall welfare by 11%. Combining both approaches — raising slower-growing breeds at lower stocking densities — resulted in a 63% improvement, the largest gain across all scenarios.

In terms of emissions, the model revealed that:

• Lowering the stocking density from 36 to 24 kilograms per square meter increased emissions by 1%
• Using the moderately slow-growing Ranger Classic breed increased emissions by 15%
• Using the slow-growing Hubbard JA757 breed increased emissions by 30%
• Combining both changes increased emissions by 17 to 32%

Most of the increase came from greater feed use due to longer rearing periods. However, emissions were partly offset by greater breeder efficiency. Systems using slower-growing chickens need fewer parent birds due to their longer fertility periods and lower mortality rates. Moreover, the model assumed the same feed mix was fed to both the fast-growing and slower-growing breeds, so actual emissions for slower-growing birds might be lower with optimized diets.

The researchers were unable to conduct a corresponding welfare assessment for broiler breeders, as they only found one study on the topic. These chickens are important to consider, however, as they endure severe feed restriction in conventional systems. Slower-growing lines may reduce or, in some cases, eliminate the need for this restriction, but the evidence remains limited.

Animal Welfare And Environmental Trade-Offs

The researchers calculated trade-off ratios by comparing emissions increases to welfare improvements. A higher ratio indicates a potentially greater conflict between the two. Reduced stocking density had the lowest ratio (around 0.1), while slower-growing breeds had higher ratios (roughly 0.4 to 0.9). Combining both changes offered a more balanced result (about 0.3 to 0.5).

The Swedish Context

Even in the highest-emission scenarios, chicken meat from higher-welfare systems still produced 2.4 to 2.7 times fewer emissions than pork and 17 to 19 times fewer emissions than beef, according to Swedish data.

Sweden already has relatively strong animal welfare laws, though its typical stocking density (36 kilograms per square meter) is similar to other European countries. Nonetheless, the findings suggest that switching to slower-growing breeds could offer meaningful welfare gains even in already well-regulated systems.

Takeaways For Advocates

This study shows that improving broiler chicken welfare — particularly by switching to slower-growing breeds — will likely increase GHG emissions. However, these increases are modest compared to the climate cost of other meats, and they come with substantial welfare benefits. Thus, advocates can use this research to promote slower-growing breeds as a welfare priority, while supporting feed and system improvements to limit emissions.