Literature Review Comparison of Feed Conversion Between Cattle Sheep Fish and Chickens
Proc Natl Acad Sci U S A. 2018 May 15; 115(20): 5295–5300.
Sustainability Scientific discipline
Comparative terrestrial feed and land apply of an aquaculture-dominant world
Halley E. Froehlich
aNational Center for Ecological Analysis and Synthesis, University of California, Santa Barbara, CA, 93101;
Claire A. Runge
aNational Eye for Ecological Assay and Synthesis, University of California, Santa Barbara, CA, 93101;
bArctic Sustainability Lab, UiT The Arctic University of Kingdom of norway, 9019 Tromsø, Norway;
Rebecca R. Gentry
cBren School of Environmental Scientific discipline and Direction, University of California, Santa Barbara, CA, 93106;
Steven D. Gaines
cBren School of Environmental Science and Management, University of California, Santa Barbara, CA, 93106;
Benjamin S. Halpern
aNational Eye for Ecological Analysis and Synthesis, Academy of California, Santa Barbara, CA, 93101;
cBren School of Ecology Scientific discipline and Management, Academy of California, Santa Barbara, CA, 93106;
dSection of Life Sciences, Imperial College London, SL57PY Ascot, United kingdom of great britain and northern ireland
Significance
Studies are revealing the potential benefits of shifting human being diets abroad from meat and toward other protein sources, including seafood. The majority of seafood is now, and for the foreseeable time to come, farmed (i.e., aquaculture). Every bit the fastest-growing food sector, fed aquaculture species increasingly rely on terrestrial-sourced feed crops, simply the comparative impact of aquaculture versus livestock on associated feed and country use is unclear––especially if human diets shift. Based on global production data, feed utilise trends, and human consumption patterns, nosotros simulate how feed-ingather and land employ may increase by midcentury, but demonstrate that millions of tonnes of crops and hectares could be spared for well-nigh, merely not all, countries worldwide in an aquaculture-ascendant future.
Keywords: aquatic farming, livestock, beast feed, land use, human diets
Abstract
Reducing nutrient production pressures on the environment while feeding an always-growing human population is one of the grand challenges facing humanity. The magnitude of environmental impacts from food production, largely around land employ, has motivated evaluation of the environmental and health benefits of shifting diets, typically abroad from meat toward other sources, including seafood. All the same, total global take hold of of wild seafood has remained relatively unchanged for the last two decades, suggesting increased demand for seafood will mostly have to rely on aquaculture (i.due east., aquatic farming). Increasingly, cultivated aquatic species depend on feed inputs from agricultural sources, raising concerns around farther straining crops and land use for feed. However, the relative touch and potential of aquaculture remains unclear. Hither we simulate how different forms of aquaculture contribute and compare with feed and land employ of terrestrial meat product and how spatial patterns might change by midcentury if diets motility toward more than cultured seafood and less meat. Using country-level aquatic and terrestrial data, we show that aquaculture requires less feed crops and state, fifty-fifty if over one-third of protein production comes from aquaculture by 2050. Notwithstanding, feed and land-sparing benefits are spatially heterogeneous, driven by differing patterns of production, trade, and feed composition. Ultimately, our study highlights the future potential and uncertainties of considering aquaculture in the portfolio of sustainability solutions around one of the largest anthropogenic impacts on the planet.
What nosotros consume and how we produce nutrient has tremendous affect on the planet, specially with an expected population of virtually 10 billion people past 2050 (1, 2). Approximately 40% of terrestrial land is already cultivated or grazed (3), which has contributed to rapid loss of species diverseness and habitats (four), unsustainable freshwater use (4, five), substantial pollution in terrestrial and aquatic ecosystems (half-dozen), and big greenhouse gas emissions (vii) over the past century. The extent and caste of impacts driven by our food systems has led to multiple environmental and wellness studies quantifying the benefits of shifting diets away from meat to typically more seafood and plant-based consumption (7, 8). However, the rise growth in seafood consumption and the increasing importance of aquaculture (i.e., aquatic farming) to meet that demand (nine)––fifty-fifty if global reform of fisheries comes to fruition (10)––raises new questions and concerns for time to come sustainable food production if diets proceed to shift to more seafood.
Aquaculture is the fastest-growing food manufacture in the world and already produces more biomass than either wild seafood or beef (three, 9), making it a fundamental part of future food production. Fed aquaculture (finfish and crustaceans requiring direct feed input) currently comprises over 70% of cultured seafood production (excluding seaweed), and is rapidly growing, mostly from freshwater finfish, similar carp (11). The remaining biomass comes virtually entirely from molluscs, filter-feeding taxa (e.g., mussels and oysters) that excerpt resources from the surrounding environment, thus requiring no added feed (i.eastward., unfed) (ix). Considerable attention has focused on fish-based inputs of aquaculture feeds (12), but due to limits of such aquatic sources, fed species at present largely and increasingly depend on terrestrial feed crops (11, xiii). Thus, aquaculture now competes for crop resources with livestock, the free energy industry, and directly human consumption––raising concerns of aquatic farming's impact on global food resiliency (fourteen). Notwithstanding, land-level patterns of state employ arising from ingather-based feeds from aquaculture are not well understood, in big office because most models only consider livestock and merchandise can confound the exact area of land attributed to animal feed within a given country (xv). Aquatic and terrestrial farmed animals differ in feed requirements and energy efficiency (feed conversion to biomass) and increasing use and inclusion of certain ingather types (e.thousand., maize) that support the continued rise in fauna production could take significant consequences for feed and land utilise if diets shift to more cultured seafood and less terrestrial protein.
Animal production is expected to significantly increase by 2050 to meet per-capita homo consumption demands (hateful product increase ± SD = 52 ± 12%; Materials and Methods and Fig. ane) (7, xvi). However, there is considerable scope for shifts in the type and corporeality of protein consumed, as demonstrated past the rapid growth of poultry production overtaking and rivaling other meat products worldwide (17). Using scenario-based simulations, we explore how shifts in global diets toward cultured seafood and away from meat, and associated increases in aquaculture product levels, in plow change the comparative force per unit area on feed-ingather requirements, and how that might translate to changes in surface area and location of land use for crops and grazing. Nosotros compare iii scenarios in 2050 that differ in the sources of animal protein: (i) business-as-usual consumptive trends and production needs (i.due east., more terrestrial than aquatic protein); (2) the additional 2050 meat demand is instead met entirely by aquaculture with electric current ratios of freshwater and marine production (mixed scenario); (iii) the additional 2050 meat demand is replaced by predominantly marine aquaculture (marine scenario). The alternative "seafood" scenarios bound realistic paths for different aquaculture sources due to uncertainties around future consumer tastes (eighteen) and geographic distinctions of marine versus freshwater product (9). To simulate feed and state-use consequences of each scenario, nosotros account for the heterogeneity in fauna feed compositions, increased use and homogenization of crop-based feed, increases in futurity production efficiencies of animals and crops, and global trade patterns (seven, 16). In all cases, we simulate the major protein sources: beef, dairy moo-cow, hog, goat, sheep, broiler chicken, laying hen, freshwater and marine finfish, crustacea, and mollusc (Materials and Methods).
Current and average projected 2050 alive-weight biomass of each taxonomic grouping and animal production scenario. Scenarios are based on a mean 52% (SD ± 12%) increment in full, live-weight concern-equally-usual (BAU) fauna production necessary to meet projected global edible protein demand in 2050. fw, freshwater.
Results and Discussion
Futurity aquaculture production (mixed and marine scenarios) would need to increase more than 4 times current levels to replace an expected (boilerplate) 46% increase in meat and provide the equivalent edible protein (Fig. ane). Several studies––on which we base of operations our scenarios––project the aquaculture business organization-as-usual scenario approximately doubling by 2050 (vii, 19, 20). Our seafood scenarios essentially double baseline projections, requiring production levels merely over what would be required for more prescribed global pescetarian nutrition trends (bold constant wild catch) (7). Increasing predominantly fed marine aquaculture (marine scenario) appears less viable, requiring an nearly 13-fold increase, bold molluscs continue contributing 25% of product as they exercise presently and freshwater production still increases business as usual (boilerplate 120%). This is primarily a consequence of fewer countries currently producing marine aquaculture, marine production consisting of mostly molluscs with lower edible biomass (SI Appendix, Table S1), and overall less product (approximately one-tertiary of all aquaculture). However, futurity marine production is expected to continue to grow quickly (9) and expand into offshore waters (21), which may effect in differing local to global impacts of marine versus freshwater aquaculture.
Assessing vii of the nearly dominant crops increasingly used in farmed animal diets (Fig. 2A ), nosotros notice that even when aquaculture provides over 1-tertiary of simulated biomass produced under both seafood scenarios, over 90% of feed crops still go to produce terrestrial animals. This highlights the comparative magnitude of pressure that land-based species place on the terrestrial food arrangement, and the relative efficiency of aquatic organisms (Fig. twoB ). Shifting toward cultured seafood-dominant diets reduces annual feed-crop requirements by 598.7 (SD ± 172.5; mixed) to 564.7 (±168.one; marine) one thousand thousand tonnes compared with business organization equally usual. Notably, the variability (SD) around the mean feed-crop estimates demonstrates the potential hundreds of millions of tonnes of savings that could come from global improvements in future brute efficiencies (livestock, poultry, and aquaculture). Notwithstanding, while total ingather requirements are reduced under the 2050 seafood scenarios, full use of the vii feed crops assessed in this report yet rises to two times current levels due to an expanding population, increased per-capita consumption of animal protein, dairy cows and laying hens allowed to increase, and a greater proportion of these crops included into future animal diets (Materials and Methods and SI Appendix).
Mean feed-ingather requirements for each creature protein production scenario. Total average (±SD) global feed-crop equivalence (tonnes) for each (A) crop type and (B) animal group for the four scenarios: current (baseline), business organization-as-usual (BAU) 2050, proportional substitution of 2050 meat production with mixed (freshwater and marine) aquaculture, and meat substitution from primarily marine sources. fw, freshwater.
The future area of cropland needed for feed increases under all future scenarios, simply we observe that millions of hectares are spared with human diets based on a larger proportion of cultured aquatic protein (mixed: total spared land ± SD = 75.9 ± 13.5 1000000 hectares; marine: 69.9 ± 13.three million hectares) (Fig. 3 A–C ). Again, the variability (SD) illustrates the potential tens of millions of hectares that could be spared with ubiquitous increases in creature efficiencies (Fig. iiiC ). However, savings are non uniform. While most countries spare cropland (hateful ± SD = 180 ± 5 regions; 413.7 ± 73.7 1,000 hectares), substantial increases in land use for feed occur in well-nigh a dozen countries (Fig. threeD ). Several regions take chances requiring xxx% or more cropland for feed than under the business-as-usual scenario (Fig. 3B ), including Chile, Egypt, and Norway, which are all significant producers of fed marine aquaculture and assumed to domestically supply a portion of feed if the associated crop is produced in land (Materials and Methods). Information technology is important to notation this does not necessarily mean an expansion of total cropland, but rather an increased utilise of cropland (existing or new) for feed. Notably, compared with business organisation as usual, the aquaculture scenarios reduce cropland brunt for feed in biodiverse regions of conservation business organization, such every bit Brazil (25% spared, equal to eleven.half-dozen ± 2.1 million hectares).
Amount and location of changes in cropland for feed under different protein hereafter scenarios. Percent of feed-based cropland spared (blues) or used (reds) to run into crop demands based on a comparison of business-as-usual (BAU) 2050 meat-based diet to seafood nutrition scenarios, from (A) mixed (freshwater and marine) aquaculture or (B) predominantly marine aquaculture. C depicts the total average land utilize (±SD) from crops for feed under each scenario and (D) displays the distribution of FAO regions that would spare more and use more in country use. Countries in gray practise not change or are not applicable.
State-use savings from shifting toward aquaculture-based diets are even greater when we business relationship for land used for grazing. Roughly iii-quarters of all agronomical land is currently used for grazing ruminants (cows, sheep, and goats) (iv). We used published estimates of global animal grazing feed ratios to reflect the amount of regional livestock biomass produced from pasture (versus crop feed) to summate the extent of land required per unit of measurement of ruminant biomass (Materials and Methods) (5). After accounting for grazed and cultivated land, switching future growth in meat consumption to seafood spares an extent twice the size of Bharat (747–729 million hectares mixed and marine scenarios, respectively; Fig. 4). Savings are, once more, non evenly distributed (country-level mean ± SD = 3.21 ± xi.two million hectares; range = 0–141 million hectares). Under both aquaculture scenarios, nigh all countries reduce their total feed production footprint with more than cultured seafood than meat (Fig. 4A ). For instance, Brazil could spare an average 12 times more land under both seafood scenarios if grazed land is considered––the nearly savings of any country from reduced reliance on grazed livestock (see SI Appendix for full listing).
Amount and location of changes in total state apply nether unlike 2050 animal product scenarios. (A) Percent of land spared (blues) or used (reds) accounting for grazing and crop demands based on a comparing of business-as-usual (BAU) 2050 meat-based diet to seafood nutrition scenarios, sourced from mixed (freshwater and marine) aquaculture. Marine results are equivalent to the mixed scenario outputs and thus not depicted. (B) Full boilerplate country utilize from crops (rainbow colors) and grazing (green color) for feed of each scenario. SDs of cropland use were too small at the grazing scale and are thus not presented (see Fig. 3 for SD). Countries in grayness exercise not change or are not applicable.
Increases of molluscs (unfed cultivated species) in time to come diets can result in an obvious reduction in required feed, and thus country use. Our future simulations assume consumption of molluscs remains proportionally constant beyond all scenarios (25% of aquaculture product). A diet shift toward more bivalves could thus provide poly peptide and greater spared land, too equally possible ecosystem services, including improved local h2o quality, littoral protection, and even habitat for wild species (22). Due to a lower edible percentage, a insufficiently greater volume of molluscs would accept to be cultured, which could negatively affect aquatic systems (due east.yard., divert energy flow) (23). Molluscs may also exist more than sensitive to environmental stressors (east.g., ocean acidification) (24), and crave relatively consistent and arable primary production (i.e., phytoplankton) to grow effectively (25). These factors, combined with global preferences for finfish, may limit dietary shifts to farmed molluscs. Ultimately, increases in aquaculture production may non exist as limited by biophysical or space constraints equally terrestrial product, but instead by economical, cultural, and political factors (21).
Shifting diets to more cultured seafood has comparatively lower impact on feed and land employ, merely does not eliminate such pressures and could effect in other environmental and dietary shortcomings. Electric current aquaculture engineering and best practices can help reduce some negative effects, including pollution and disease (26), but exercise not negate stresses that can arise from improper planning and weak oversight, such every bit escapes and habitat degradation (27). With globalized markets, local aquaculture-based impacts could exist minimized by more even distribution of aquatic farms (i.e., "spread the wealth" and impact) in the near suitable areas (due east.g., offshore) (21). However, the high ingather-input levels simulated here would likely compromise the micronutrient benefits of fish, emphasizing the importance of other alternative-feed sources (e.g., omega-3 eicosapentaenoic acid and docosahexaenoic acrid) from an environmental and human health perspective (28).
Our futurity scenarios assume crop use increases to support connected growth in animal product, given other feed-based resources are express, namely forage fish (e.chiliad., anchovies, herrings, sardines, etc.) used for fishmeal and oil (xi, 29, 30). Capture fisheries landings, including forage fish, have remained relatively unchanged for several decades (nine), meaning additional growth of farmed fauna production––specially aquaculture, which now uses virtually (∼73%; pigs and poultry 25%) of the fishmeal and oil (29)––will increasingly rely on alternative feedstuffs, such as crops. In the future, it is likely the decades-long tradition of feeding forage fish to farmed animals will continue, but in continually smaller proportions and/or to select, higher-value species (eastward.g., salmonids) (11, 29). Whether greater inclusion of crops and other alternative feeds (e.g., omega-three algae) (31) will reduce angling pressure on forage fish or other unreported aquatic species fed to farmed animals (32) depends on supply (scalability and cost) of nutritionally equivalent feeds (29) and other emergent demands (e.one thousand., greater homo consumption of forage fish) (33). Nonetheless, it appears the future potential to ease exploitation and use forage fish in other ways exists, peculiarly if incentives and management move toward sustainable feed practices.
Minimizing future impacts of the human diet on terrestrial and aquatic environments will rely on trade-offs betwixt domestic and imported supplies of the type of animal protein and feed from efficient and sustainable producers (15). Aquaculture is a food system and thus volition have an bear on on the environment. If greater adoption of cultured seafood into human diets did occur, like to the rise of poultry (17), policy interventions that protect biodiversity from cropland expansion, like the Wood Lawmaking for Brazil (34), would remain important, and greater understanding the effects of aquaculture on wild aquatic systems at an ecosystem level would be critical (35). What this written report demonstrates is the relative potential, just not sole solution, for reducing one of the largest pressures on the planet (agronomical land use) compared with current nutrient system trends. Incentives and policies because aquaculture as part of the portfolio of food sustainability solutions at a local to global scale––from supporting access and adoption of new or improved feed ingredients and species efficiencies, to strategic farm siting and seafood distribution––could provide substantial benefits for humans and the environment into the future (36).
Materials and Methods
Nosotros fake meat production and associated crop and grazing country requirements for livestock, poultry, and fed aquaculture species for 230 Nutrient and Agriculture Organization of the United Nations (FAO) regions (196 countries) under three future scenarios. "Regions" account for countries and territories according to International System for Standardization country coding. Estimates for future animal feed and associated country utilize were calculated using a combination of current country-level estimates of primary animal production around the globe, reported future protein demands and trends for 2050, country animal feed composition from data repositories and literature, and country crop production of major feed types and associated projected efficiencies of those crops. Below nosotros describe each component and assumption of the model in detail. Electric current values were used to parameterize the "baseline model" and test operating model outputs against other feed and land-use estimates to ensure realistic results were produced (SI Appendix). All analyses were performed in R, Version iii.4.1 (37).
Animal Product.
To prepare baseline ("electric current") weather condition, we outset compiled state-level estimates of the near globally important protein sources past book (tonnes) for livestock and poultry (which includes beef, pork, sheep, goat, dairy moo-cow for milk, broiler craven, laying hen for eggs) and aquaculture [which includes fed freshwater finfish and crustaceans, marine and stagnant (referred to equally marine henceforth) finfish and crustacean, and unfed molluscs] (3, nine, 38). Unfed silver and bighead carp were excluded from the analysis (9). We extrapolated average biomass of hens and dairy cows, equally just head-count FAO data were available. We did this by estimating the conversion factor (1 caput = X tonnes) of broiler chickens and beef cows based on reported total global number (head count) and FAO-estimated biomass of these animals (conversion factors for hen = 0.0014 tonnes; dairy cow = 0.23 tonnes).
A large proportion of livestock (beef, dairy cows, sheep, and goats) are fed via grazing (38), then we distinguished between animal biomass produced from crop-based feed (Eq. 1) versus grazing (Eq. 2). Presently, the majority of agronomical country use is pasture for grazing, and land-utilize implications for conservation are very different for crop versus grazing areas (four). However, data on the ratio of feed to grazing over a ruminant animal'southward lifetime for each state are unavailable. To capture a level of per-country differences, we assigned regional proportions of grazing (versus feed) derived from Mekonnen and Hoekstra (five) to all ruminants and associated countries (SI Appendix, Tabular array S2). All nonruminant animals (excluding unfed molluscs) were assumed to be 100% fed. The biomass values were calculated equally
where b a,j is the estimated feed-based biomass (tonnes) of fauna a in state j, B a,j is the total biomass of animate being a of country j, and P j is the proportion of animate being biomass of country j that is produced past feed (nongrazing). Biomass of grazed livestock (G r,j ) of ruminant (r) (i.e., cattle, goats, and sheep) was calculated every bit
where B r,j is the full biomass (tonnes) of ruminant livestock r of country j and (1 − P j ) is the proportion of (ruminant only) biomass of country j that is produced from grazing.
Future (year 2050) business-as-usual biomass production values were calculated based on boilerplate projected change in wealth-driven protein consumption from previous studies, disproportionate production increase expected to occur in developing regions, and ratios of average alive-weight total biomass of an brute to consumable protein (SI Appendix, Table S1). To capture a level of uncertainty in modeling human consumptive futures, nosotros randomly sampled (n = 500) beyond a maximum (+xx%) and minimum (−20%) range of per centum animal productions originally derived from Tilman and Clark, and informed past Alexandratos and Bruinsma (16) who reported ∼20% divergence in predicted future meat-production requirements [see Hunter et al. (39) for details] (SI Appendix, Table S3). To business relationship for the bulk of product growth anticipated to occur inside developing nations, nosotros also added or subtracted a constant of 10% to the projected percent production increase for developing and developed countries, respectively, based on FAO reports (nine, 38) (SI Appendix, Table S3). We used the resulting averages in projected alive-weight fauna product for the crop-feed and land-use calculations (Fig. 1). Under all future scenarios, animal production growth occurs where it already exists, proportional to electric current levels, and wild catches are causeless constant.
We chose seafood scenarios (includes freshwater and marine species) that allowed usa to explore and clearly compare some of the consequences and plausibility of substantial global nutrition shifts toward more cultured seafood and less meat. One major assumption of our written report is that countries accept the socioeconomic ability to switch to seafood. This may be difficult for certain countries, particularly in more than developing, arid climates (due east.chiliad., some African nations). Investment and growth in aquaculture is growing considerably in such regions (nine), but the actual ability for aquaculture to substitute for cattle (the largest agricultural feed and land user) is beyond the scope of this study. In add-on, product is driven by need, and it is unknown if hereafter populations could or should value (socially, culturally, and economically) seafood more than state-based meat production. Ultimately, the scenario approach allows us to highlight the possible implications of a more aquaculture-dominant world.
Ingather-Feedstock Calculations.
Although a diverseness of products can enter the diet of a farmed fauna, we focused on the most arable and normally reported inputs across animal and crops types, specifically wheat, maize, soy, rapeseed, pulses, barley, and cassava products (3, vii, 14). Together these inputs currently contribute to 74% of terrestrial feed and accept been consistently and increasingly present in global ingather-based feeds over the last 50 y (SI Appendix, Fig. S1) (3). If the significant linear trend (linear model: P < 0.001, Radj 2 = 0.85) toward homogenization of ingather-based feedstocks persists to 2050, these 7 crops would contribute an average of 88% (SE ± 0.six%) to animal feed.
We account for land-level variability of crop-based feed at the animal level:
C i,a,j =b a,j A i,a F a c i,j ,
[3]
where C i,a,j is the estimated crop-equivalent tonnage of total i crop needed to feed animal a in country j, b a,j is the total biomass of brute a of country j on feed (Eq. 1), A i,a is the average proportion of feed from crop i for animal a (from feed composition), F a is the feed conversion ratio of animal a, and c i,j is the harmonizing constant of crop i, country j (derived from reported FAO commodity residual sheets) (three).
For the electric current-based model, we derived information on proportion of each crop type in brute feed stocks (boilerplate composition, A i,a , Eq. 3) of livestock, poultry, and fed aquaculture (finfish and crustaceans) from existing sources (3, seven). Initial average animal feed-crop compositions were derived from Tilman and Clark (7). We assigned the regional feed proportions for aquaculture to their associated countries. However, these feed-crop proportions were non originally differentiated for freshwater and marine species. More than specifically, estimated feed composition in Tilman and Clark did non account for aquatic-based inputs––which can be substantial for fed aquaculture (east.g., protein and oil contributions from fodder fish) (eleven, 13). Most freshwater species (e.g., bother) tend to have smaller proportions of aquatic inputs compared with marine species (e.thou., salmon). To address this, we decreased the Tilman and Clark pulse proportional estimates (a big protein-based input) in aquaculture feeds to meliorate reflect the larger use of aquatic-based sources (iv% less for freshwater species and no pulse inputs for marine species) (11, 13). Regions without distinct aquaculture feed composition estimates (n = 30) were assigned the boilerplate (other), which included Due east Europe and Republic of Independent States and Modest Island countries and territories.
For futurity scenarios, we account for increasing trends of crop inclusion and feed homogenization into the diets of farmed animals (SI Appendix, Fig. S1) by adjusting the relative proportional contribution of crops in feed of all groups based on the respective linear trends of global FAO feed values (SI Appendix, Fig. S2). Nosotros increased the average animal crop-feed proportion (A i,a ) of wheat (2%; Radj 2 = 0.30, F-stat = 23.4, df = 51, P < 0.001), maize (xi%; Radj 2 = 0.86, F-stat = 323.2, df = 51, P < 0.001), soy (1%; Radj ii = 0.57, F-stat = 70.7, df = 51, P < 0.001), and cassava (two%; Radj 2 = 0.71, F-stat = 129.vii, df = 51, P < 0.001), decreased barley (−4%; Radj 2 = 0.43, F-stat = 38.1, df = 51, P < 0.001), and left rapeseed (Radj 2 = 0.06, F-stat = 3, df = 51, P = 0.09) and pulse (Radj 2 = −0.01, F-stat = 0.76, df = 51, P = 0.37) proportions unchanged. On average, the increase resulted in eight% (SD ± 5%) greater ingather inclusion across regional animal diets in 2050. In the effect irresolute the average animal-feed composition exceeded 100% of the diet, nosotros decreased maize contribution until diets balanced (SI Appendix, Table S4). These increases in crop contribution into the diets of farmed animals represent feed homogenization that can exist driven past limits of other source feeds, including fish-based inputs that accept remained constant while brute production (livestock and aquaculture) continues to increase (eleven, 29, 40). Nosotros tested the sensitivity of the model to animal-feed composition by comparing all future scenarios with compositions held constant versus the above increases (SI Appendix, Fig. S3). Greater inclusion and homogenization of feed, coupled with increased production, translates to a 27% (±two%) greater use of these crops in our simulations, predominantly from maize and cassava. Thus, the relative differences in feed crops and land use of the seafood scenarios to business equally usual are more meaningful than the accented differences to current levels that do not account for other terrestrial inputs. We also recognize nosotros simulate a more farthermost example of hereafter crop diet inclusion, which could be reduced with non–ingather-based alternative sources if they go available and economically competitive to crops feed stuffs.
To business relationship for uncertainty and possible average improvements in animal feed efficiencies (F a ), the baseline current model and all future scenarios were calculated 500× from randomly sampled values pulled from uniform distributions of feed-conversion ratios. Parameter F a is a unitless metric that describes the efficiency of an beast to convert feed to biomass (tonne input per tonne gained), and thus can be used to summate feed requirements based on biomass of an organism. Currently, in that location is no dataset of land-level efficiencies (v). Instead, we looked across primary and gray literature for realistic ranges for all animal groups (SI Appendix, Table S5), specifically analyzing the aquaculture regional efficiencies and temporal trends reported by Tacon and Metian (11, forty) and regional efficiencies reported by Mekonnen and Hoekstra (five) to bound F a ranges. For aquaculture, a linear tendency in improved efficiencies results in an average 2050 F a equal to 1.1 (SE ± 0.04) (F-stat = 25.6, df = 174, Rtwo adj = 0.12, P < 0.001), which nosotros set as our minimum for the aquaculture groups, creating comparable distributional trends (SI Appendix, Figs. S4 and S5). In fact, the salmon manufacture already reports achieving feed efficiencies of 1.1 (41). For livestock and poultry, the majority of efficiencies across taxa and regions for the feed-based categories ("industrial" and "mixed") tend to be less than 20 (SI Appendix, Fig. S5; median = 5.twoscore, Qane = 3.30, Q3 = 12.viii) (5). Nosotros set our ranges based on the global, taxonomic estimates, which resulted in comparable patterns [SI Appendix, Fig. S5 and Table S5; livestock and poultry F a (n simulations = 500) median = six.10, Q1 = 3.30, Q3 = ix.13].
One time we estimated the required amount of each dry-matter ingather feed (tonnes) from the proportions of animal biomass that comes from feed (versus grazing; b j ), average animal-feed composition (A i,a ), and feed-conversion ratios of each animal (F a ), we then harmonized our baseline model outputs to FAO country-level feed-crop equivalence values (Eq. 3). More specifically, for each country a harmonizing abiding (c i,j ) was derived from the FAO commodity-balance estimates so our boilerplate feed-crop outputs approximately reflected the absolute FAO values for each crop type in accordance with other studies (3, 42). Harmonizing provides a realistic and consistent baseline of feed crops, while assuasive additional disaggregation by other factors (42); in our case, animal production blazon. In improver, use of the commodity FAO outputs provides the crop equivalence relevant for calculating country use.
Trade of crops varies amidst countries, but is not sufficiently reported to make up one's mind the exact area of land attributed to animal feed (versus product for direct man consumption or biofuels) inside a country. To capture this heterogeneity, we employed a balanced-trade approach (i.east., trade is causeless to remainder crop deficits of regional production, with no trade barriers) (xv), which measures total tonnage (¢ i,j ) of each feed crop i in country j from the summation of domestic production (D i,j ) and export (E i,j ):
E i,j = (C i,a,j −D i,j )e i,j ,
[6]
where C i,a,j is the estimated tonnage of i crop needed to feed animal a in state j (from Eq. 3), d i,j is the proportion of domestically produced crop i in land j, and due east i,j is the global proportional contribution of exports of crop i from state j. These formulations assume that the amount of each crop used for feed within a country matches the proportions of each domestic crop produced (d i,j , calculated from full, current domestic supply of product and imports; Eq. 5) (three) and that countries that consign crops continue to exercise and so to match their current proportional contribution to global trade of the specified crop (e i,j ; Eq. 6) (3). Thus, we assume current net-exporting countries see any domestic feed deficits not accomplished by the proportion of domestic production, and that both proportions (d i,j and e i,j ) remain constant beyond all time to come scenarios. While future global product patterns will be driven by economic atmospheric condition and marginal efficiencies of increased production across space, predicting new and/or divergent expansion from current patterns is outside the telescopic of this report. Our goal was to highlight potential consequences of uneven production and trade given realistic (i.due east., current) patterns.
Land-Use Calculations.
Total cropland and grazing land were separately calculated based on our estimates of full crop-feed requirements of each country (¢ i,j ; Eq. 4) and animal biomass of ruminants from grazing (1000 r,j ; Eq. 2). Total hectares of cropland (U i,j ) used to produce feed-crop i in country j across all poly peptide sources was calculated as
where ¢ i,j is the total tonnage of i feed crop in country j (from Eq. four) and h i,j is the expanse-yield ratio of i crop (ha t−i) in land j. We then translated G r,j into area of country (hectares) needed to graze livestock (g r,j ) as
where β is the area-biomass constant (72.four ha tonne−one) for ruminant livestock to scale our estimates to the current global pasture guess (4), since the specific country-level ratio of intensive versus extensive farming biomass is unknown. Our values thus provide a simplified baseline for relative comparison of future alternative production scenarios and do not account for possible intensification feedbacks betwixt crops and grazing that could reduce future pasture needs.
Total area-yield ratios (h i,j ; Eq. 7) now and in the time to come were based on FAO yield estimates (3). Where estimates were non available for a given country, nosotros used the regional average for the associated FAO region. Time to come values were calculated based on FAO 2050 global projections of increases in production efficiencies for each ingather (wheat = 27%; corn = 22%; soy = 28%; rapeseed = 43%; pulses = 50%; barley = 17%) (16). Simply cereal percentages were differentiated betwixt global and developing nations (developing: wheat = 31%; corn = 31%). No estimates were given for cassava or any other root vegetable, so country averages (32–33%) were assigned and appear consistent with plausible future improvements (43). We followed FAO'south consignment of "adult" and "developing" nations for each country.
Supplementary Material
Supplementary File
Acknowledgments
Nosotros thank the reviewers of this manuscript for their expertise and thoughtful insights. This research was a collaborative endeavor conducted by the Open up-Sea Aquaculture Expert Working Group and Amend State-utilise Decisions Good Working Group, supported by SNAPP: Science for Nature and People Partnership, a partnership of The Nature Conservancy, the Wild animals Conservation Society, and the National Centre for Ecological Analysis and Synthesis (Proposal SNP015).
Footnotes
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Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5960322/
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