Grass-Fed Versus Grain-Fed: The Science

Grass-Fed versus Grain-Fed Beef: The Science

Is grass-fed beef more environmentally friendly in contrast to conventional?  A recent University of California–Davis research study evaluated conventional versus grass-fed beef (Klopatek et al., 2022).  They evaluated four natural methods of raising cattle that included no feeding of antibiotics or hormones. Their results show that the time to market, land use, and global warming potential are all higher for grass-fed beef and weight at slaughter is lower. Other papers show that carbon sequestration does not reduce greenhouse gas sufficiently to outweigh these drawbacks.

The table below summarizes their yield and environmental effects of the four methods of beef production.  Results below are per Kg of Hot Carcass Weight, which reflects the remaining weight after head, hide and internal organs are removed.  Comments follow to explain results.

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

 Weight at Slaughter (Kg)Dressing %1Global 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 days63261.8%4.7993318.71.280.15
Grass-fed 20 mos.47950.3%6.744657.6511.30.01
Grass-fed 20 mos. + Grain-fed 45 days55157.5%6.6567813.89.820.08
Grass-fed 25 mos.57053.4%8.3112508.859.640.01
Figure: Grassfed versus Grain-fed Beef: A Comparison of Results (Klopatek et al., 2022)

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 results show that grass-fed beef does not demonstrate substantial improvement in environmental outcomes.  Clark and Tilman (2017) explain why: Grass-fed beef requires more land use than grain-fed beef, because the pasture, grasses and fodder have lower macronutrients and digestibility compared to grain feeds, and require the animals to be fed for 6-12 months longer to achieve desired weight.  Grass-fed beef’s longer lifetime results in higher methane emissions, which raises greenhouse gases, although carbon sequestration with natural grasslands was not measured.  Studies on organic farming show that carbon sequestration occurs until the land is at carbon capacity; then additional sequestration appears to stop (Adewale et al. 2019).  Clark and Tilman (2017) 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.”

The previous studies did not test for carbon sequestration, which is the primary argument why grass-fed beef is environmentally better than grain-fed beef.  However, the UN’s Food and Agriculture Organization (FAO) Status of the World’s Resources report, Figure 4.4, shows the results of 3 studies measuring carbon sequestration in kg/m2 for various forms of land.  This figure is included below. The studies show that the highest carbon sequestration occurs in boreal regions (far north: Canada, Scandinavia, Russia) with long cold winters and coniferous (evergreen) trees.  The lowest carbon sequestration occurs in the tropics.  The carbon sequestration in soil observed for the three regions showed that pastures do not rank high in carbon sequestration, relative to “All natural”, forests, grasslands and shrubland.

Figure: UN FAO (2015) Soil carbon studies for various land uses

One can conclude from these studies that in some regions pasture outperforms cropland to some extent, but rarely performs as well as ‘all natural’, forests, shrublands, and in boreal regions, natural grasslands.  Furthermore, the Klopatek et al. (2022) study indicates that if all U.S. cattle were converted to grass-fed, beef production would be reduced to 27% of current supply, because of increased land use requirements.  Therefore, the UN IPCC is recommending moving away from grass-fed beef to more intensive agriculture (grains) or better yet, a plant-based diet. Movement toward a plant-based diet will enable more lands to revert to natural forests, shrublands and grasslands, which do show considerably better carbon sequestration than pasture.

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

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.

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.

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/.

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