Engineering Biology for Climate & Sustainability

Case Study 4: Engineering cattle gut microbiomes to reduce methane emissions in American agriculture.


Public awareness of the environmental impacts of meat consumption is growing, motivating some consumers to consider plant-based alternatives or lab-grown meat. However, many consumers are likely to continue to eat meat and consume dairy out of choice or necessity and it is thus useful to pursue opportunities to decrease the climate impacts of animal husbandry. Livestock produce 14.5% of the world’s greenhouse gas emissions, and 61% of those emissions come from beef (41%) and cattle milk (20%). Reducing the emissions from cattle would thus be a significant contribution to global climate goals.[1]

Cows are ruminants, meaning they have four-chambered stomachs. One chamber, the rumen, ferments grass and other vegetation that is otherwise indigestible. Gases such as methane and carbon dioxide are produced as bioproducts of this fermentation. This case study considers the engineering of cattle microbiomes to reduce the release of such by-products. The public reception to meat or dairy from such cows is uncertain on both domestic and international fronts. For some, engineering ruminant microbiomes is a logical step in a long history of domesticating animals to serve human priorities; others may hold a more precautionary approach and purport that the potential impacts on cattle, environmental, and human well-being are unknown and potentially unknowable without assuming unacceptable risk.


[1] Breeding and management approaches have already made cattle production significantly more efficient over recent decades, with fewer cattle being reared to feed more people.

Nontechnical considerations and social dimensions

Solutions landscape:
  • Ethical / societal – Could methane be better managed with alternative farming practices?
  • Ethical / societal – How will the economic and consumer viability of this approach compare to cultured meat production?
  • Policy / regulatory – Could non-engineered microbes that could decrease methane emissions be used as a cattle “probiotic”?
  • Economic – How would the engineering of cattle microbiomes affect meat and dairy market value?
Benefits and consequences:
  • Ethical / societal – What impacts might this have on the health and well-being of the cattle involved?
  • Ethical / societal – How would engineered cattle microbiomes affect digestive nutrient uptake and therefore meat and dairy content? Would any differences impact taste, quality, or safety of food products?
  • Ethical / societal – What are the anticipated impacts of cattle with engineered microbiomes on other fauna, compared to the impacts seen today?
  • Policy / regulatory – How will meat and/or dairy from such cattle be regulated/labeled? Will meat or dairy from such cows be regulated as genetically engineered foods?
Micro-level impacts:
  • Economic – What local industries or practices, such as commercial manure and compost manufacturing operations, might be impacted by this?
  • Ethical / societal – How might excretions from cattle with engineered gut microbiomes affect micro- or macro-organisms in a given ecosystem?
Macro-level impacts:
  • Security – Will international markets lead to global spreading of engineered microbes? If so, what consequences might that have?
  • Economic – How could it impact market segmentation between organic and conventional meat and dairy?
Competing values and priorities:
  • Economic – Do ranchers have any incentive to reduce methane emissions? Would a methane tax be an appropriate incentive?
    • What would the effects of a positive duty, such as a tax reduction for methane mitigation, be in comparison to that of a negative duty such as a methane tax? Which would be more effective and which would be easier to implement?
  • Ethical / societal – How do consumer concerns about climate change intersect with the concerns of some consumers about the application of engineering approaches to livestock?
Last updated: September 19, 2022