A model for ‘sustainable’ US beef production

The amount of sustainable beef the United States can produce is plotted as a function of the utilization level of current pastureland in Fig. 1 (quantified in mass units, left axis, or as the percentage of today’s beef availability of 460 g per person per week, right axis). Despite the recent doubling of distillers’ grain utilization, by-products still provide only ≈10% of today’s beef feed consumption. By-products alone could therefore support a rather small sustainable beef industry, even when disregarding the minimum dietary roughage required for healthy cattle nutrition. With the added utilization of all current beef pastureland (f = 1), the weekly per-capita beef availability increases to 205 g, or 45% of today’s per-capita beef consumption. Cutting this pastureland use in half (reducing pastureland occupation to ≈135 million ha, corresponding to f = 0.5) by abandoning less productive grasslands reduces beef availability only slightly, to 200 g or 43% of present values. This 2 percentage point difference in beef availability may arguably be too small to outweigh the environmental benefits of leaving this unproductive marginal pastureland for wilderness conservation.

Fig. 1: Per-capita weekly availability of ‘sustainable’ beef as a function of the utilized fraction f of current beef pastureland (approximately 0.3 billion ha). At any f value along the horizontal axis, the overall feed available for beef is the sum of the small fixed contribution of by-products (bottom grey rectangle, derived in the text and the Supplementary Information) and the f-dependent pasture contribution. This overall metabolizable feed available for beef is recast as beef availability (left axis) using beef’s energy conversion, ≈0.03 available beef kcal per metabolizable energy (ME) feed kcal3,4,23. At any f value, the pasture-based feed energy contribution (the integral of the yield function from 0 to f) is added to the above fixed by-product contribution to form the overall feed energy the sustainable beef can utilize at that f value. Beef availability is also shown (right axis) as the percent of today’s beef supply (≈460 g per person per week) that the sustainable feed can produce. Open squares highlight 0.1 f increments. The inset shows the assumed utilized yield function in metabolizable kg dry matter pasture per ha per year, also as a function of the fraction f of current pastureland used. See Supplementary Information for further details. As no data providing a direct estimate of today’s national mean pasture mass yield exist, we show here our indirectly derived estimate of ≈430 utilized kg dry matter ha−1 yr−1 (horizontal grey line)3,4. The equivalent pasture yield shown in the inset is the assumed ME yield divided by the representative mean forage energy density3,4, 2,140 kcal ME (per kg dry matter), as described in detail in the Supplementary Information. It is not an estimate of the overall grass above-ground productivity, but only of its utilized—eaten and metabolized—fraction. Full size image

Importantly, any of the sustainable beef scenarios considered above would free up the ≈32 million ha of high-quality cropland the beef industry currently uses for crop-based feed4, as well as all the reactive nitrogen and irrigation water annually applied to them—3.1 billion kg and 27 billion m3, respectively4. These uses of cropland, reactive N and irrigation water represent 21, 28 and 24% of the respective national total agricultural uses of these resources. It would also avert the GHG emissions associated with the current use of these high-quality croplands4, which amounts to about one-third18 of conventional beef’s current total (≈267 billion kg CO 2eq yr−1). These resources could be reallocated to the production of more efficient alternative food items (foods that require less environmental resource per unit protein) or conserved, negating further environmental degradation.

Of the four considered limiting resources, land is unique in that it is finite, unlike the other three, whose availability can be technologically augmented. In Fig. 2, we thus quantitatively explore the consequences of reallocating the ≈32 million high-quality cropland hectares (currently used to produce the crop-based portion of US beef cattle feed) to the production of several plant food alternatives (see Supplementary Information). We assume that all the considered alternatives enjoy their current mean yields, from which it follows to also assume that they receive the same mean resource inputs per ha as they currently do. Reallocating land currently used for the production of feed for beef to the production of feed for pork, for example, would yield about four times as many pork calories as the lost beef calories, or an approximate three-fold net gain (Fig. 2a, right axis) and just under three times the protein, or an approximate net protein doubling (Fig. 2b, right axis). Figure 2 shows that land reallocations to any of the considered alternatives would enhance the delivery of human-edible calories now provided by beef 2- to 16-fold (Fig. 2a) while increasing protein delivery 2- to 24-fold (Fig. 2b). The considered land reallocations thus offer large caloric and protein gains per high-quality cropland hectare while reducing agricultural resource uses.

Fig. 2: Alternative per-capita food energy and protein delivery associated with reallocating the ≈32 million high-quality ha currently used to produce crop-based feed for US beef cattle to the shown alternatives. a, Alternative energy delivery. b, Alternative protein delivery. See Supplementary Information for specific calculation details. Plant and animal alternatives are shown in green and red, respectively. The top blue horizontal lines show the amounts that beef currently delivers. The (nearly overlapping) middle and bottom blue lines show sustainable beef availability when using all (f = 1) or half (f = 0.5) of the pastureland currently allocated for beef. Full size image

In Fig. 3, we perform a nutritional analysis of the reallocation of the high-quality cropland beef currently use to other plant- and animal-based alternatives by comparing the macro- and micronutrient delivery by beef and the alternatives. This shows that, principally due to the very low feed-to-food protein conversion efficiency of beef23, its low protein yield—37 kg ha−1 yr−1 compared with soybeans’ 914 or peanuts’ 667 kg ha−1 yr−1—results in land reallocations maintaining or expanding the delivery of protein, energy and carbohydrates (but differing amino acid compositions may limit the kg-for-kg interchangeability of beef and some alternatives). Reallocating land to 8 of the 14 plant-based alternative items adds to protein and energy delivery half or more of the current full per-capita dietary delivery (see Supplementary Information for a definition of the latter). At almost 2 kg protein per week, the added per-capita protein delivery by the most protein-dense alternative, soybean (or its derivative tofu), is enough to fully meet the dietary protein needs of four additional people. This means that every individual who commits to halving their beef consumption and reallocating the freed cropland to soybeans can not only fully recoup the lost nutrition due to reduced beef availability, but also meet the full protein needs of four additional people. While adding carbohydrates and sugar intake may raise concerns, the added carbohydrates are almost exclusively complex and of the low glycaemic load and slowly digested variety, and the sugar addition is trivial compared with the ≈400 kcal d−1 of added sugar24 the mean US adult uses, allaying this concern. All plant alternatives provide more protective total and soluble fibre intake than beef’s zero. Similarly, the intake of most vitamins and minerals is maintained or enhanced under the reallocation. Vitamin B 12 is a well-known exception, which only the reallocation to poultry and dairy increase modestly. This observation is the basis for the important and firmly established25 necessity for B 12 supplementation of pure plant-based diets.

Fig. 3: Nutritional consequences of producing 'sustainable' beef (that use only industrial by-products and the full pastureland currently used by beef; that is, at f = 1) and the associated reallocation of cropland (currently used for producing feed for beef) to each of the shown alternatives. Green text is used for plant-based items and red for animal-based items. Each coloured cell shows the amount of a nutrient delivered by the alternative food item minus the net loss due to reduced beef production (the loss of the full conventional beef amount minus the smaller gain due to permitted 'sustainable' beef), expressed as a percentage of the delivery of the same nutrient by the truncated mean American diet (MAD) (details in the Supplementary Information). For instance, cell (1,1) shows that if the cropland currently used for beef feed production is fully reallocated to soybeans, the added soy protein minus the net loss of beef protein would amount to a 350% increase in the protein content of the MAD. Full size image

Changes in the amount of unsaturated fatty acids are mixed and mostly modest except for soy, tofu and pork, which increase the intake of these beneficial fatty acids appreciably. For soy products and the animal alternatives, these positive dietary changes may be potentially offset by additions of saturated fat, with the animal alternatives also adding cholesterol. The overall addition of protective phytomicronutrient intake is highly varied, with significant gains limited to soy, peas, sweet potatoes and snap beans. Lastly, while the sodium intake increases, undesirably, under the reallocation, even the highest additions associated with reallocation to sweet potatoes are ≤ 100 mg, which is about 4% of the recommended daily intake of 2,300 mg, and thus trivial compared with delivery by added salt. Focusing on all plant and poultry alternatives and all nutrients, we conclude that the land reallocations we consider here would be nutritionally safe and mostly beneficial. This conclusion joins the voluminous literature documenting the health benefits of primarily plant-based diets10,12,26,27,28,29.

Finally, we quantify the environmental consequences of full cropland reallocation from beef feed to the alternatives considered above. For the three key environmental metrics impacted by agriculture (water usage, GHG emissions and fertilizer burdens1,3,4,30), Fig. 4 shows the resources saved by the reallocations (the resource use by the replaced beef minus the resource use by the plant alternatives) as a percentage of the total resource use by current beef production. A value of 40%, for example, means that after the land reallocation, the alternative crop uses 60% of the current resource use by the usurped conventional beef. The mean resource savings by all alternatives are 40–80% of the use by conventional beef, thus offering very significant potential improvements. Note that while enhanced methane production by pastured (as distinguished from mostly grain-fed18) beef results in a 20–30% higher CO 2eq burden21, all the plant alternatives offer net GHG savings.