Grass-Fed Versus Grain-Fed: The Science

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Grain-Fed Outperforms Grass-Fed for Land Use, Efficiency and Climate Change – but Carbon Sequestration?

Carbon Sequestration is Higher In Natural Lands – Not Grazed Lands

Aquaculture versus Fish Farming

Greenhouses versus Open Fields

Grain-Fed Outperforms Grass-Fed for Land Use, Efficiency and Climate Change – but Carbon Sequestration?

Remembering that beef generates a high rate of greenhouse gases per kilogram of meat, might grass-fed beef be more environmentally friendly compared to conventional beef? Grassfed is certainly a more natural way to raise cows and usually more humane. However, conventional farming has optimized product for a given level of feed. Herrero et al. (2015) indicate that grazing-based systems contribute slightly less than 1% of edible energy to the human food supply, even though grazed land makes up 75% of agricultural land (IPCC, 2014, p. 836).

A recent, more detailed study from the University of California–Davis compared conventional and grass-fed beef (Klopatek et al., 2022). They evaluated four natural cattle-raising methods that excluded antibiotics and hormones. Their findings show:

Advantages Grass-Fed Beef: Lower energy requirements, lower smog potential.

Disadvantages Grass-Fed Beef: requires more time to market, uses grossly more land, has a higher global warming potential, and provides lower animal weight at slaughter.

Other research indicates that carbon sequestration does not offset greenhouse gas emissions enough to overcome these disadvantages.

The table below summarizes the yield and environmental impacts of the four beef production methods. The results are presented per kilogram of Hot Carcass Weight, which is the weight remaining after removing the head, hide, and internal organs. Comments follow to explain the results.

Table: Yield and Environmental Outcomes of Grass-Fed versus Grain-Fed Beef

	Weight at Slaughter (Kg)	Dressing %1	Global Warming Potential2 (CO2e/Kg)	Water Consumption3 (Liters/Kg)	Energy Use (MJ/Kg)	Land Use4 (m2 yr/Kg)	Smog Potential5 (O3 eq/ Kg)
Conventional: Grain-fed 124 days	632	61.8%	4.79	933	18.7	1.28	0.15
Grass-fed 20 mos.	479	50.3%	6.74	465	7.65	11.3	0.01
Grass-fed 20 mos. + Grain-fed 45 days	551	57.5%	6.65	678	13.8	9.82	0.08
Grass-fed 25 mos.	570	53.4%	8.31	1250	8.85	9.64	0.01

Notes:

1. Dressing Percentage: Percentage of meat to total body weight after slaughter.
2. Global Warming Potential (GWP): Grass-fed beef suffers increased enteric methane (digestive burps) due to slower growth, poorer digestibility and lower yield.  In these results and two others, conventional out-performed grass-fed in reducing greenhouse gases; but the studies did not consider carbon sequestration. 
3. Water consumption: Does not include rainfall.  With conventional beef, 96% of water is used to grow feed; 3% for drinking water.  The main water used for grass-fed includes watering of irrigated pastureland.
4. Land Use: Indicates the required land to produce 1 kg of beef in meters²/year.
5. Smog Potential: Includes greenhouse gas Nitrous Oxide (NOx) emissions, nitrogen application on farmland.

For full research article, see: https://pmc.ncbi.nlm.nih.gov/articles/PMC8867585.

These research findings indicate that grass-fed beef does not offer significant environmental benefits. Clark and Tilman (2017) explain that grass-fed beef requires more land than grain-fed beef because pastures, grasses, and fodder have lower nutrient density and digestibility compared to grains. As a result, animals must be raised for an additional 6 to 12 months to reach the desired weight. This extended lifespan leads to increased methane emissions, contributing to higher greenhouse gas levels, although the potential carbon sequestration from natural grasslands was not accounted for. Clark and Tilman (2017, p. 8) conclude: “Indeed, for all indicators examined, ruminant meat (beef, goat and lamb/mutton) had impacts 20–100 times those of plants while milk, eggs, pork, poultry, and seafood had impacts 2–25 times higher than plants per kilocalorie of food produced.”

Carbon Sequestration is Higher In Natural Lands – Not Grazed Lands

Clark and Tilman (2017) did not examine carbon sequestration, a key argument supporting the environmental benefits of grass-fed beef over grain-fed beef. Soil acts as a major carbon reservoir because microbes and bacteria transform leaves and other organic matter into soil organic carbon. According to the UN Food and Agriculture Organization’s (FAO) Status of the World’s Resources report, Figure 4.4 presents data from three studies measuring carbon sequestration in kg/m² across different land types. This figure, shown below, reveals that the highest carbon sequestration occurs in boreal regions—such as Canada, Scandinavia, and Russia—characterized by long, cold winters and coniferous forests. Conversely, tropical regions exhibit the lowest carbon sequestration rates. The studies indicate that pastures rank lower in carbon sequestration compared to “All natural” lands, forests, grasslands, and shrublands. Research on organic farming suggests that carbon sequestration continues until the soil reaches its carbon saturation point, after which sequestration increases level off (Adewale et al. 2019).

The graph indicates that in some regions, pasture performs better than cropland to a certain degree, but it rarely matches the carbon sequestration levels of natural ecosystems such as forests, shrublands, and, in boreal regions, natural grasslands. Additionally, the Klopatek et al. (2022) study shows that converting all U.S. cattle to grass-fed would reduce beef production to just 27% of current levels due to increased land requirements. Consequently, the UN IPCC recommends shifting away from grass-fed beef toward more intensive agriculture (such as grain production) or, preferably, adopting a plant-based diet. Transitioning to a plant-based diet would allow more land to revert to natural forests, shrublands, and grasslands, which have significantly higher carbon sequestration potential than pasture.

Can we confirm that natural grasslands outperform grazed grasslands? Bai and Cotrufo (2022) examined carbon sequestration in natural grasslands compared to grazed pastures by analyzing findings from various studies. Their results indicate that increased grazing reduces carbon sequestration. Light grazing led to a median decrease of 4% in carbon sequestration, while heavy grazing caused losses ranging from 10% to 27%. Heavy grazing contributes to soil compaction and shorter grass, which in turn increases erosion.

Aquaculture versus Fish Farming

Clark and Tilman (2017) provide context that 45% of fish production is from fish farms.  Fish farms within natural waters have similar greenhouse gas emissions to non-trawling fishing, and both have similar GHG emissions to chicken, pork and dairy.  Trawling fishing (where nets are drawn across the seabed) and enclosed tank fish farms have “several times more greenhouse gases” (Clark and Tilman, 2017).

Greenhouses versus Open Fields

Greenhouses have much better land use and slightly better eutrophication and acidification than open fields.  However, open fields have lower energy requirements and cause fewer greenhouse gases than greenhouses (Clark and Tilman, 2017).

References

Bai, Y., Cotrufo M. F (2022) Grassland soil carbon sequestration: Current understanding, challenges, and solutions. Science, 5 August 2022, vol. 377 issue 6606  pp. 603-608.

Maria Vincenza Chiriaco, Simona Castaldi, Riccardo Valentini (2022) Determining organic versus conventional food emissions to foster the transition to sustainable food systems and diets: Insights from a systematic review.  Journal of Cleaner Production 380 (2022) 134937, Elsevier Ltd.

Michael Clark and David Tilman (2017) Comparative analysis of environmental impacts of agricultural production systems, agricultural input efficiency, and food choice.  Environ. Res. Lett. 12 (2017) 064016, IOP Publishing.

Environmental Working Group (2024) EWG’s shopper’s guide: The Dirty Dozen™. From: https://www.ewg.org/foodnews/dirty-dozen.php.

FAO and ITPS. (2015). Status of the World’s Soil Resources (SWSR) – Main Report. Food and Agriculture Organization of the United Nations and Intergovernmental Technical Panel on Soils, Rome, Italy.

IPCC (2014) Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment
Report of the Intergovernmental Panel on Climate Change [Edenhofer, O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K.
Seyboth, A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. Savolainen, S. Schlömer, C. von Stechow, T. Zwickel and J.C.
Minx (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

M Herrero, S Wirsenius, B Henderson, C Rigolot, P Thornton, P Havl´ık, I de Boer, and P. J. Gerber (2015) Livestock and the Environment: What Have We Learned in the Past Decade? Annu. Rev. Environ. Resour. 2015. 40:177–202.

Sarah C Klopatek, Elias Marvinney, Toni Duarte, Alissa Kendall, Xiang (Crystal) Yang, and James W Oltjen, (2022) Grass-fed vs. grain-fed beef systems: performance, economic, and environmental trade-offs. J Anim Sci. 2022 Feb; 100(2): skab374. Pub Med Central. See: https://pmc.ncbi.nlm.nih.gov/articles/PMC8867585/.

Smith P, Bustamente H, Ahammad H., Clark H., Dong EA. (2014) Agriculture, Forestry and Other Land Use (AFOLU). In Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the International P Climate Change, Cambridge University Press, Cambridge UK and New York NY.

Wedderburn-Bisshop, Gerard (2024) Consistent, Inclusive Emissions Accounting Identifies Agriculture as the Leading Cause of Climate Change.