The Dublin Declaration of Scientists on the Societal Role of Livestock

Implications Aspects of human anatomy, digestion, and metabolism diverged from other primates, indicating evolutionary reliance on, and compatibility with, substantial meat intake. Implications of a disconnect from evolutionary dietary patterns may contribute to today’s burden of disease, increasing the risk for both nutrient deficiencies and chronic diseases. Meat supplies high-quality protein and various nutrients, some of which are not always easily obtained with meat-free diets and are often already suboptimal or deficient in global populations. Removal of meat comes with implications for a broad spectrum of nutrients that need to be accounted for, whereas compensatory dietary strategies must factor in physiological and practical constraints. Although meat makes up a small part ( 3 million years (Mann, 2010, 2018). Dietary divergence of the hominin line from other apes on the African continent was induced by gradual climate change, which resulted in the expansion of drier grasslands and semi-forested regions. Digestible plant foods became less readily available than in wetland forests, but grazing animals were abundant. This led to a dietary shift towards fat and protein, accompanied by the physiological and metabolic adaptations that culminated in modern humans (Figure 1). Figure 1. Overview of the role of meat in human nutrition and of the potential complications if global meat consumption was to be restricted beyond a critical threshold. Ancestral food intake habits have been determined based on a variety of methods, including anthropometry (e.g., cranio-dental changes, suggesting less emphasis on grinding and more on biting and tearing of flesh) and the analysis of the fossil record through a combination of scanning electron microscopy of teeth to reveal microwear patterns, stable isotope analysis in bone and teeth enamel to unravel the trophic level, and exploration of butchery practices, suggesting consumption of ungulate animals. Additional information was obtained using mathematical modeling (e.g., optimal foraging theory), and the study of modern hunter-gatherers as surrogate models of ancestral dietary practices. Due to a process of ‘encephalization’, humans have a larger brain size than would be expected for their body size. To sustain an expansively large brain, energetic compensation was required during hominin evolution. When examining individual organs, the brain mass surplus (and its energy requirement), is closely balanced by the reduction in size (and energy requirement) of the gastrointestinal tract. This is not surprising, considering the gut is the only organ that can sufficiently vary in size to offset the metabolic cost of a larger brain (Aiello and Wheeler, 1995). This process required a shift from a diet high in bulky plants of low digestibility (requiring voluminous fermentation chambers such as a rumen or cecum, or an extensive colon), to a higher-quality diet where foods are more energy dense and require less digestive processing. In temperate grass and woodland environments, this equates to an animal-derived protein-rich and fat-rich diet (Speth, 1989). Based on their digestive system, humans are classified as omnivores, falling between their frugivorous anthropoid relatives (e.g., chimpanzees) and true carnivores. With a simple stomach, relatively elongated small intestine, and reduced cecum and colon, the human gut is suggestive of reliance on a high-quality diet in which meat was predominant. The intestinal length to body length ratio of humans (5:1) is like dogs (6:1) and markedly different to grazing mammals (cattle, 12:1). Another measure of digestive system structure is the gastrointestinal surface area to body surface area ratio, with humans (0.8:1) once again being more similar to carnivores (dogs, 0.6:1) than grazing mammals (cattle, 3:1) (Henneberg et al., 1998). Even compared with their closest evolutionary relatives, the chimpanzees and gorillas, humans have a distinct digestive tract that shows differences favoring reliance on higher-quality foods. The great apes, for instance, have the greatest volume of gastrointestinal tract devoted to the colon (>50%) for the fermentation of low-grade plant materials, compared with humans at 200 geographically diverse hunter-gatherer societies show a median energy reliance on animal-sourced foods of around 60% (Cordain et al., 2000). A disconnect from evolutionary dietary patterns may contribute to today’s burden of disease, at least in some age groups (Mann, 2010). This argument is likely to be more consequential during childhood, based on the intensified nutrient requirements for growth and brain development in the early phase of life. Animal-sourced foods, such as meat, are the best source of nutrient-rich foods for children aged 6–23 months (a finding supported by the World Health Organization), leading to compelling benefits on cognitive functions (Balehegn et al., 2019). Drawing on studies from 95 cultural groups, animal-sourced foods—and meat from ungulates particularly—were the most frequently mentioned food groups in child dietary patterns from an evolutionary perspective (Iannotti et al., 2022). Studies examining the health implications for children and youth in the transition from gatherer-hunter-fisher diets to agriculture subsistence reveal nutritional deficiencies, infection, and metabolic perturbations associated with reduced meat consumption and dietary diversity (e.g., Chinique de Armas and Pestle, 2018). Essential Nutrients in Meat It has been argued that public health policies need to assess the above-mentioned evolutionary knowledge when developing food-based dietary guidelines, especially for children (Iannotti et al., 2022). Today, meat has a key dietary role to play based on the density and bioavailability of its nutrients. Restricting its intake would imply that these nutrients will need to be supplied by other foods, or by fortification or supplementation. While this is theoretically possible, it may not be straightforward in practice, due to limitations at the level of resources, culinary skills, dietary culture and habits, or nutritional awareness and knowledge. Food intolerances and allergies (e.g., gluten, soy, or pea protein) further complicate the suitability of meat-free diets. As for all restrictive diets that exclude nutrient-rich food groups, whether by choice or necessity, the impact is particularly relevant for populations with elevated needs, such as children, women of reproductive age, older adults, and individuals in low- and middle-income countries. Below we list the key points of attention that individuals on meat-free diets need to consider. Protein quality Not all proteins are of equal nutritional value. It is essential to consider the content and digestibility of the indispensable amino acids (IAA) in a food, as these are the nutrients needed to synthesize bodily proteins. By acknowledging these aspects, encapsulated in the term ‘protein quality’, the efficacy of a food as a protein source can be better understood. In practice, protein quality is arguably best described using the Digestible Indispensable Amino Acid Score (DIAAS; Moughan, 2021). Its calculation requires information on the IAA contents of a food and provides estimates of their true ileal digestibility. A food is given a score of 1 or higher if the absorbed IAA are all utilizable, whereas a lower score indicates that only a portion of the absorbed IAA are available for utilization. For meat, DIAAS values fall in the range of 0.8–1.4, whereas values for most traditional plant proteins are markedly lower (Marinangeli and House, 2017). In general, values for legumes range between 0.4 and 1.1, which are like nuts (0.4–0.9) but generally higher than cereal foods (0.1–0.8). In plants, some IAAs are limiting, and digestibility is reduced due to complex plant cell structures and the presence of fiber and anti-nutritional factors (the effects of which can be partially attenuated through processing). Consequently, with some exceptions (e.g., certain soy-based foods), many protein-rich plant foods fail to reach the ‘good source of protein’ criterion (Marinangeli and House, 2017). When considering the nutritional value of protein sources, it is thus not sufficient to simply consider protein content. Low-quality protein sources are not fully utilizable unless combined with complementary protein sources, meaning that even an individual achieving the recommended gross protein intake may be deficient in IAA if the DIAAS score of their diet is 100 countries faced inadequate protein supply for their populations after consideration of bioavailability. These were predominantly lower-income countries, and the poorer bioavailability was attributed to low dietary diversity, including minimal access to animal-sourced foods. Although it is often stated that individuals in high-income countries overconsume protein, that is, above the recommended daily allowance (RDA) of 0.83 g per kg bodyweight, this assertion ignores the effect of protein quality and is based on the minimum need to avoid loss of lean muscle mass in healthy populations. This is, however, not necessarily an optimal amount, as many populations may benefit from higher intake levels (e.g., twice the stated recommendation), especially in view of muscle building, pregnancy, lactation, healthy aging, and in the case of acute or chronic disease (Leroy et al., 2022). Meeting the same protein target with plant options, having typically lower DIAAS values, is feasible but requires specific dietary strategies. Besides for those deficient in protein, the effects of dietary protein quality are particularly important for people with relatively low energy intakes and targets for daily protein higher than the RDA. Micronutrients The current understanding of the bioavailability of nutrients in meat is most advanced for protein and amino acids, with varied understanding for other essential nutrients. Several of these nutrients are of key importance for global health, not least because they are to be considered crucial for the human brain: iron, zinc, and vitamin B12 (in addition to long-chain omega-3 fatty acids, see below). If not supplemented, these nutrients are either obtained exclusively from animal-sourced foods or are more bioavailable in those foods. In addition, meat contains a range of other B vitamins that can be limited in micronutrient-poor diets based on non-fortified cereal staples, including thiamine and niacin. However, nutrient levels vary considerably between categories of meat (e.g., ruminant meat, pork, poultry, and processed meats), as well as carcass cuts and fattiness. These differences can be further modulated by animal genetics, activity level, sex, and feed (e.g., at the level of essential fatty acid content). Organ meats are particularly reliable sources of vitamins A and D, iron, zinc, folate, selenium, and choline, of which the supply is often limiting at the global level, even in high-income countries (Stevens et al., 2022). Most attention has been given to iron and zinc as essential micronutrients with acute and chronic health outcomes for deficiency, related to physical and cognitive development, physiological functioning, blood health, and immunity (Beal and Ortenzi, 2022). These minerals are contained in a wide range of foods of both animal and plant origin. However, plant foods often contain compounds that bind to these minerals and reduce their absorption (e.g., fiber, phytate, and phenolic compounds). Also, zinc is better absorbed from animal-sourced foods where it is in a protein-bound form, similar to the heme iron from animals which is more readily bioavailable than the non-heme iron found in plants. It has been estimated that the average bioavailability of iron and zinc in ruminant meat is 2 and 1.7 times as high, respectively, as that of pulses, like beans, lentils, and peas (Beal and Ortenzi, 2022). As a further complication, iron intake alone may be insufficient to treat anemia because other micronutrients, including vitamin A and B vitamins, are needed for iron mobilization and hemoglobin synthesis. Even if vegetarians have iron intakes above the recommended levels, and often even higher than those of omnivores, this usually still results in lower iron status. Similarly, meeting the recommended dietary intake is no guarantee for adequate zinc status. To account for the above-mentioned differences in bioavailability and to avoid deficiencies, higher recommended intakes are specified for individuals consuming diets with higher plant-sourced and lower animal-sourced food content (FAO/WHO, 2004). Adequate intake of vitamin B12 is essential for normal blood function and neurological function. The vitamin is critical for nerve cell myelin synthesis and, with folate, for DNA synthesis. It is converted into a range of coenzyme forms in the human body, which play essential roles in numerous critical metabolic pathways. A range of neural and mental health related issues have been linked to vitamin B12 deficiency (e.g., fatigue, depression, poor memory, and mania) potentially leading to permanent damage in infants and toddlers. Almost all dietary intake of vitamin B12 is in the form of animal-sourced foods, meat being the most important source. Long-chain omega-3 fatty acids Omega-3 fatty acids are a family of polyunsaturated fatty acids of varying chain length and functionality in the human body. They are found in plants (α-linolenic acid in particular), but the longer chain forms, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are only found in marine organisms and land herbivores. They are both critical agents in terms of cell membrane structure and tissue health (especially for the brain, heart, and retina), while also acting as precursors for a range of eicosanoids that affect the cardiovascular system and mitigate chronic inflammation. Human studies show numerous associations of DHA status, in particular with cognitive function, visual acuity, and brain development in children. The chain elongation and desaturation pathway common in most animals should theoretically allow the conversion of the shorter plant omega-3 fatty acids to EPA and DHA. However, in humans this pathway is inefficient, requiring humans to consume EPA and DHA preformed from animal tissue (Baker et al., 2016). Vegetarians and vegans tend to have lower levels of EPA and DHA in their plasma and erythrocytes, despite a higher status of α-linolenic acid (Rossell et al., 2005; Chamorro et al., 2020). Other bioactive molecules and the role of the food and diet matrix Besides containing a wide spectrum of essential nutrients, meat is a unique source of various non-essential yet biologically active molecules, such as taurine, creatine, anserine, carnosine, and 4-hydroxyproline (Wu, 2020). Their potential health advantages relate to healthy aging, skin and bone health, immunity, and the prevention of obesity and cardiovascular pathologies. These molecules are often overlooked in nutritional assessments and still represent only a fraction of the much broader and variable range of biochemical compounds that can be present in meat, modulated among other factors by the type of animal feed, and the diet at large (Barabási et al., 2020). Their impact on health is uncertain but hints to the importance of the entire food matrix, while cautioning against nutritional reductionism (Leroy et al., 2022). Meat is more than the sum of its individual nutrients (Klurfeld, 2023), for example, by regulating the absorption and metabolism of other nutrients. A growing body of evidence supports the inclusion of animal-sourced foods in food-based dietary interventions for improving the nutritional status of populations, as compared to nutrient supplementation or fortified product programming (Bhutta et al., 2013). This may be partially explained by the potential health effects of many uncharacterized (or even unknown) compounds that are present in meat, but the complexity likely goes further. The bioavailability of nutritional compounds ultimately depends on the food and diet matrix. In recent years, food-based dietary guidelines have shifted towards recommending dietary patterns rather than prescriptive nutrient or food quantities (Herforth et al., 2019). This trend acknowledges cultural differences within and across countries, but also the public health importance of consuming patterns of food groups within a wholesome diet matrix. Meat consumed in appropriate levels serves as a keystone food in this system. For instance, resource-poor countries suffer from highly prevalent stunting and other forms of malnutrition, in part due to inadequate dietary diversity (including low intake of animal-sourced foods) and a heavy reliance on a single staple (typically cereal) for daily energy needs (Ranum et al., 2014). Meat can help improve mineral bioavailability particularly in the context of plant-centered diets that are high in phytates (e.g., from maize). Contribution of Meat to Global Nutrient Supply Using global food production, loss, and use data, it has been possible to understand how global nutrient supplies from food matches up to global population requirements. The DELTA Model® has shown that meat contributed the majority of the global vitamin B12 supply, as well as a quarter of vitamin A (in retinol equivalents; mostly from organ meats and poultry), and high proportions of other B vitamins and several minerals (Figure 2; Smith et al., 2022). This data should be seen in combination with the sufficiency of global supply: the model has estimated that the supply of iron, zinc, vitamin A, and vitamin B12 exceeds global requirements by <10%, uncorrected for bioavailability, making meat’s contribution all the more critical. This contribution should be weighed against the fact that meat makes up a small part (<10%) of both global food mass and energy, providing further evidence for its nutrient density. Figure 2. The contribution of food groups to the global supply of nutrients and dietary fiber from food, with all forms of meat for human consumption (including organ meat and processed meats) highlighted. The values for protein and the indispensable amino acids have been corrected for bioavailability from the contributing food items, but not for minerals and vitamins (note that, for instance, the average bioavailability of iron and zinc in ruminant meat is 2 and 1.7 times as high, respectively, as that of pulses; Beal and Ortenzi, 2022). Adapted from Smith et al. (2022). This global picture does not capture regional variation. In the case of unprocessed red meat, the average per capita daily consumption is estimated at just 7 g in South Asia, 24 g in Sub-Saharan Africa, 36 g in the Middle East and North Africa, 45 g in high-income countries, 51 g globally, 68 g in Latin America and Caribbean, 87 g in Southeast and East Asia, and a sizable 114 g in Central or Eastern Europe and Central Asia (Miller et al., 2022). Regions with the lowest intake also show the highest prevalence of undernutrition (Adesogan et al., 2020; Stevens et al., 2022). Potential Global Implications of Meat Restriction There are potential nutritional benefits and risks associated with restricting meat, which vary by context, population, life course phase, and replacement food. In many low- and middle-income countries, particularly in Sub-Saharan Africa and South Asia, meat intake is very low, and undernutrition is high (Miller et al., 2022). These populations could benefit from an increased rather than reduced meat intake (Adesogan et al., 2020). Thus, global efforts to moderate meat intake for environmental or other reasons should be careful not to restrict its growth in populations where consumption is already low, as this could hinder progress towards reducing undernutrition and thereby not address human suffering and the stifling of economic development (Balehegn et al., 2019). Even in high-income countries, a reduction in meat from current intake levels (e.g., in view of non-communicable risk reduction; see elsewhere in this Issue, Johnston et al., 2023), needs to be considered in conjunction with its impact on nutrient status (Beal and Ortenzi, 2022; Stevens et al., 2022). Particular phases of the life course necessitate nutrient-dense, bioavailable foods to fulfill requirements: women of reproductive age, pregnant and lactating women, infants and young children, and older adults. Changing diets in high-income countries, which tend to be associated with decreasing red meat intake, parallel rising iron deficiency (for the USA, Sun and Weaver, 2021). For women of reproductive age, iron requirements can be challenging to meet on any diet but restricting ruminant meat—among the densest sources of bioavailable iron—complicates the problem in the absence of careful efforts to consume iron-fortified foods or supplements. Over 20% of these women in the United States and United Kingdom are deficient in iron alone, while one-third of these women in the United States and one-half in the United Kingdom are deficient in one or more micronutrients (Stevens et al., 2022). Besides leading to anemia, iron deficiency may also lower cognitive performance in women (Murray-Kolb and Beard, 2007), potentially affecting the healthy development of their offspring. Correlational studies show an association between iron deficiency anemia and poor cognitive and motor development, along with behavioral problems and learning difficulties which continue into middle childhood. Furthermore, low maternal zinc intake during pregnancy and lactation is associated with less focused attention and decreased motor function in neonates, while zinc supplementation in infants can lead to increased activity and functionality (Bhatnagar and Taneja, 2001). Similar arguments can be made for EPA/DHA and vitamin B12, given their key role in neural and brain health (Baker et al., 2016; Balehegn et al., 2019). When strict vegetarian upbringing results in deficiencies of these nutrients, physical and cognitive development will be compromised (Leroy and Barnard, 2020). As argued above with respect to the evolutionary implications of a dietary disconnect, young children (6–23 m) have high iron and other nutrient requirements and their development may be impacted with reduced meat intake. Although this would have to be further confirmed by a comprehensive risk assessment, several pediatric associations have already expressed their concern when it comes to vegan and, to a lesser degree, vegetarian upbringing (e.g., the German Society for Pediatrics and Nutrition Science, Swiss Federal Commission for Nutrition, and Belgian Royal Academy of Medicine). In low- and middle-income countries, numerous studies show that the consumption level of animal-sourced foods in general is positively associated with cognitive development, verbal ability, activity level, and behavior in children (Adesogan et al., 2020). Beyond these potentially confounded associations, the administration of meat in intervention studies is also known to improve the zinc and iron status of infants (Obbagy et al., 2019), as well as the behavioral, physical, and cognitive outcomes of children (Neumann et al., 2007; Hulett et al., 2014). Globally, iron and zinc deficiencies are among the most prevalent nutritional problems (Stevens et al., 2022), and meat consumption within a diverse and healthy diet shows immense potential for addressing these issues (Beal and Ortenzi, 2022). Finally, older adults are at risk of impaired cognitive function, dementia, poor bone health, frailty, and sarcopenia, among other effects of aging that may be negatively impacted by reduced intake of animal-sourced foods. Red meat in particular has been shown to improve essential functions such as muscle health and thereby protect against sarcopenia (Granic et al., 2020). Conclusion Meat is a nutrient-dense food, well suited to meeting human nutritional requirements. With a demonstrated role in human evolution, it continues to have a key role in human health and development today. Removal or large reductions of meat from the diet, as well as prevention of increases where consumption is low, either of an individual or of populations, carries a risk which must be appreciated when considering its value in future food systems (Figure 1). Moreover, a radical suppression of livestock-based systems may not only come with the nutritional complications outlined in this article but may also lead to unintended environmental consequences. As discussed elsewhere in this Issue, meat’s nutritional benefits should not be disregarded when addressing its role in the risk of chronic diseases (Johnston et al., 2023) or when performing environmental assessments (Manzano et al., 2023). Indeed, the dietary role of meat goes far beyond the provision of food mass, energy, or even protein, to numerous essential nutrients and beneficial bioactive compounds, all of which are held together in a complex food matrix.

Implications There has been a significant increase in the number of scientific articles related to “cell-based meat” (‘CBM’), which is in line with the current interest from the scientific community and consumers, but mainly from investors, food industry, and regulatory bodies. Despite the billions of dollars being invested in “cellular agriculture”, there are significant technical, ethical, regulatory, and commercial challenges to getting these products widely available in the market. In addition, the widespread adoption of such technologies can exacerbate global inequity between affluent and poor individuals and between high- and low-income countries. Current ‘CBM’ products are not identical to the products they aim to replace. First, there is still considerable dissimilarity at the level of sensory, nutritional, and textural properties, while important quality-generating steps in the conversion of muscle into conventional meat are missing. Second, many societal roles of animal production beyond nutrition can be lost, including ecosystem services, co-product benefits, and contributions to livelihoods and cultural meaning. Detailed production procedures are not available, making it impossible to corroborate the many claims related to their product characteristics and sustainability. ‘CBM’ companies arguing that the cost of all technology will eventually be significantly reduced often quote Moore’s law. However, biological systems like ‘CBM’ have natural limits and feedback mechanisms that negate this law. Introduction In alignment with an emerging Silicon Valley–style outlook on the future of food, a bold 2019 report by the think tank RethinkX claimed that by 2030 the U.S. meat and dairy industries would be bankrupt due to “cellular agriculture” taking over their traditional markets (Tubb and Seba, 2019). This claim was based on their view of how quickly precision fermentation and “cell-based meat” (‘CBM’) technology would be developed and scaled, so they could compete on price parity with traditional livestock production (Leroy et al., 2023). However, estimates on future evolutions differ wildly. For example, a 2018 report ordered by the Flemish government predicted that the consumption of “clean meat” may start in approximately 2040 (van Diepen et al., 2018). Ten years ago, however, it was already touted that “clean meat” would be available in the market by 2017 (EC, 2012). By now, it is clear that it is difficult to make predictions and that many technical challenges remain before such products can become commercially available. Nevertheless, over the past few years, billions of dollars have been invested in these technologies related to cellular agriculture (including precision fermentation and CBM) and hundreds of new start-ups have been created around the globe (Boukid and Gagaoua, 2022). The terminology for developed products is still under discussion; for recognizability, we will use the term “cell-based meat”, though the term “meat” imparts characteristics that have not been proven, as we will discuss. The reasons for proposing new protein alternatives, including ‘CBM’, are diverse and divergent, but mainly related to ethical concerns about animal welfare and the possible impact of animal protein production on the environment (Siddiqui et al., 2022). This paper briefly describes the technical, regulatory, and consumer challenges facing both precision fermentation and CBM and examines their potential to disrupt the meat and dairy industries, with a focus on ‘CBM’ as an alternative to farm animal proteins. Precision Fermentation to Engineer Proteins for Dairy and Meat Industries Precision fermentation is the process of engineering the gene sequence for a specific protein into a bacterium or yeast strain and then growing that strain in large-scale fermenters, to produce the required protein. This technology has been used for decades in the biotechnology sector. It was previously referred to as “recombinant protein production” and is used for many vaccines and drugs, such as insulin (Wood and Tavan, 2022). In the food sector, precision fermentation has been used for decades to produce enzymes for cheese making or conventional fermentation. Chymosin, used in cheese manufacturing for milk coagulation, was originally extracted from the stomachs of calves before manufacturers switched to a recombinant form of this enzyme (expressed in a range of organisms). Recently, companies have used this technology to produce key proteins for the food industry. Impossible Foods uses a precision-fermentation form of hemoglobin to give their plant-based burgers the look and smell of red meat when they are cooked. As another example, The Every Company is producing chicken-free egg products using precision fermentation technology. Until now, the major focus has been on dairy products. Around 60% of the companies in the precision fermentation space are focusing on the production of key dairy proteins. Perfect Day was the first company to release a commercial dairy product containing β-lactoglobulin. Other companies are now following their lead. One of the goals for companies like All G Foods and Eden Brew is to recreate a liquid milk, which contains both the whey and casein proteins that are needed to form a micelle, to give this product the full functionality of cow’s milk. These products will still need to have added fats, sugars, minerals, and vitamins to approach the nutritional content of cow’s milk. There has been significant investment in the precision fermentation space and many predictions that this technology is going to disrupt the traditional meat and dairy industries; however, there are many technical, regulatory, and consumer challenges that need to be addressed. The major technical challenge will be the cost of goods, with precision fermentation being significantly more expensive. For milk proteins, a range of yeast strains can produce recombinant proteins at a rate of 10–30 g/l, but these proteins then need to be separated from the yeast cells and cell debris using a variety of downstream processing techniques that can account for up to 60% of the cost of manufacture. Precision fermentation technology will also be critical for the ‘CBM’ sector to produce the various growth factors and perhaps other compounds required to culture mammalian cells. To scale-up precision fermentation, companies use fermenters at >100,000-l capacity, which will require complex engineering and energy intensive processors. In the USA, the regulatory process is relatively straightforward with the ability to use the ‘Generally Recognized As Safe’ classification. In Europe, however, it will be difficult to register precision fermentation products under the current legislative constellation, as they use genetically modified organisms in the manufacturing process. Finally, the labeling of precision fermentation products will vary considerably in different regions, and this has the potential to confuse consumers who are cautious of genetically modified products. Based on these issues, precision fermentation will be unlikely to disrupt the livestock industry but may provide high-value products for niche markets. How Close Does “Cell-Based Meat” Currently Come to Meat? Companies aspire to produce meat without using animals (Figure 1). It is touted that such ‘CBM’ will be the same as meat from farm animal(s). Meat from animals is typically derived from the skeletal muscle of slaughtered animals, though other tissues such as liver and products of the fifth quarter are also consumed, of which the amounts depend on the region in the world and local food cultures. Here, we will focus on meat derived from skeletal muscle. Currently, many hurdles remain to make ‘CBM’ despite several decades of work stemming mainly from the fields of regenerative medicine and monoclonal antibody production. These hurdles have been summarized in Thorrez and Vandenburgh (2019) and still remain. The envisioned production procedures tend to oversimplify the complexity and growth of skeletal muscle. Skeletal muscle is a tissue which is composed of several cell types, the most abundant one being myofibers. Other cell types include connective tissue cells (fibroblasts), fat cells (adipocytes), endothelial cells, and blood cells. The current focus is mainly on the expansion of myoblasts, the precursor cells to myofibers. However, it is still unclear how long cells from biopsies can be expanded, as these primary cells undergo senescence during long-term expansion. Other precursor cell types (e.g., pluripotent cells) are being explored, but the creation of these cells, as well as the efficient differentiation towards myoblasts, currently involves genetic engineering. Figure 1. Simplified schematic representation of how ‘cell-based meat’ is touted to be produced using ‘cellular agriculture’ without rearing animals. Sometimes, the expansion phase is compared to fermentation. However, there is a stark difference between growth rates of bacteria and yeast vs. animal cells. Yeast can expand well over 1000× in less than a day, whereas this takes over 10 days for animal cells. Adding other cell types, in a way that spatially is similar to muscle, involves a co-culture setup, which adds to the complexity. Myoblasts need to fuse to form multi-nucleated myotubes and these myotubes are an intermediate towards myofibers, which occurs in animals during prenatal development. These myotubes are aligned (driven by unidirectional forces between attachments to the bones) and to create a similar alignment for ‘CBM’, manufacturing techniques and edible scaffold materials need to be developed. After birth, the myofibers then grow in volume and contractile strength since the organism is actively using them. The properties of muscle from fetuses and newborns (which seldomly is consumed) are vastly different from the muscle of adult animals. Building up proteins from the contractile apparatus, which are characteristics for skeletal muscle, requires the prolonged stimulation of muscle. Such stimulation is not currently accounted for and will require bioreactor development which will significantly increase the envisioned production time. As there is no product nor protocol available, most of the claims related to the production of ‘CBM’ in view of sustainability improvements (e.g., energy or water use) seem not scientifically substantiated or remain at best speculative, especially for its environmental footprint (Lynch and Pierrehumbert, 2019; Rodríguez Escobar et al., 2021). Manufacturing challenge for cell-based meat The ‘CBM’ products are not commercialized because the current industrial production is still not economically viable due to the high production costs as well as lack of regulatory framework. In fact, one of the greatest challenges facing the scaling of ‘CBM’ manufacturing is the cost of goods for these products. This is driven primarily by the cost of the culture media, the need for high quality facilities, and the capital cost for sophisticated manufacturing facilities. The biotechnology industry has been using cell-based systems for the manufacture of monoclonal antibody therapeutics for several decades and this is an expensive technology. The use of serum-free media is standard but more expensive than the use of serum, due to the cost of the recombinant growth factors. With ‘CBM’, the final product of cell culture will be the cells themselves, which can be used as a cell slurry or induced to undergo muscle fibers differentiation. Once this step has occurred, the cells will be exceedingly difficult to handle, and this part of the manufacturing process is yet to be fully described. Many ‘CBM’ companies are claiming that the costs will be dramatically reduced using large-scale bioreactors at up to a 250,000-l scale. However, the only product registered so far is produced at a 5-l scale, so validating these systems at scale will be a major challenge. In addition, the use of antibiotics will not be permitted, and these larger scale fermentations will require around 90-days continuous sterile culture. Another claim is that ‘CBM’ manufacturing will not require the level of biosecurity used in the biopharma industry, yet most of these quality requirements are driven by the need to maintain sterile systems. The cost of large-scale ‘CBM’ facilities has been estimated at $600M U.S. and the depreciation costs of these facilities will be a major component of the final cost of goods. While interesting, other technology that is being developed for ‘CBM,’ like edible cell-scaffolds and 3D printing with multiple cell types, just add to the challenge of scaling and cost of goods. The development of blended products with plant-based material will help to reduce costs and stabilize formulation. Some companies are focusing on culturing fat cells, with the view that they will only need to add 5% of these cells to their formulations to give the product the hint of meat. Proponents of CBM frequently use the concept of Moore’s Law, the idea that the cost of production for new technologies decreases exponentially over time, to argue that this will also be the case with CBM. However, while Moore’s law has been predictive with the cost of production for physical technologies like computers and high-throughput omics methods, it has never been applied to a biological system due to the complexity of the biological events and mechanisms underpinning cell growth. Nutritional challenges for cell-based products At present, despite the claims of companies, such products are not ready for the market. To the best of our knowledge, only one lab-based food product is registered (in Singapore) and has been temporarily available in very limited quantities. In addition, production protocols are not available for independent testing by academics or regulatory agencies (Figure 2). Therefore, any claims related to nutritional content cannot be verified as such. Indeed, much remains to be inferred based on available research-scale protocols, as was conceptually analyzed by Fraeye et al. (2020). Sensory properties of meat such as texture, color, and flavor can perhaps be adjusted with food engineering techniques to create products with similar appearance to meat. However, the use of these products in downstream cooking applications may be limited as these characteristics may change during further processing steps such as heating and interaction with other ingredients. It is much harder to make statements related to nutritional characteristics, although these products can be suitable for people having adverse reactions to peas, soy, and gluten. Meat contains highly digestible proteins with essential amino acids, vitamins, and minerals (see elsewhere in this Special Issue). However, while nutrients can be added to meat replacement products, the cost (both in economic and sustainability terms) of this is unknown. Moreover, simply adding components may lead to a different bioavailability, for example, the extent and rate by which they are absorbed by the body. Figure 2. Summary of the remaining challenges and questions related to the future of ‘cell-based meat’ (‘CBM’). Regulatory and Consumer Issues Related to “Cell-Based Meat” Consumption As described by Chriki et al. (2022), an important question pertains to the legal nature of ‘CBM’: is it really meat? According to the American Meat Science Association (Boler and Woerner, 2017), the European regulation (Annex I of Regulation No. 853/2004), and other legal definitions (Ong et al., 2020), meat comes from a part (muscles and/or edible tissues) of an animal consumed as food. Therefore, ‘CBM’ does not currently qualify as meat except if we consider living cells as part of an animal (Ong et al., 2020). To be considered meat, ‘CBM’ must be sourced from an animal, proven to be safe for consumption, and be similar in composition, nutritional value, and sensory quality to meat from farmed animals, which is not yet the case (Boler and Woerner, 2017). In addition, to consider ‘CBM’ as a novel food (within EU legislation) means that it should be safe and properly labeled, so as not to mislead consumers. From a biological point of view, meat is the final product of aged muscle through a maturation process (a well-known process by butchers), just as wine originates from grape juice through winemaking. The current cellular agriculture process, however, produces muscle fibers/cells and not meat. Therefore, consumers who are familiar with what meat represents within their culinary and agricultural legacies tend to decline calling it “meat”, unlike vegan activists who see it as a welcome strategy to eliminate meat from the food system and, therefore, wish to give it maximum market potential by capturing the meat category (Gousset et al., 2022). Additionally, various societal roles of animal production beyond nutrition can be lost in the process. This includes the many ecosystem services offered by livestock, the generation of edible and non-edible co-products (e.g., hides, wool, manure, draught power, serum, blood, and fats), contributions to livelihoods, and the generation of cultural meaning. Finally, still from a societal perspective, it has been argued that ‘CBM’ may exacerbate global inequity, including increased economic disparity between regions (Mahoney, 2022). The technology risks being under the control of multinational corporations (based on patents and high technological, economic, and legal entry barriers), may lead to the creation of luxury foods, and cause a further expansion of food deserts (Mahoney, 2022). When conducting surveys in view of market acceptability, answers are often inconsistent (Gousset et al., 2022). This is not entirely unexpected, as consumers are being asked about a product which does not yet exist, with the exception of Singapore. In addition, most may not know what ‘CBM’ is and confuse it with any other type of artificial meat (e.g., plant-based imitations). Willingness to “try the product” and willingness to “consume it regularly” are also often confounded. Indeed, many respondents would like to taste the product once for curiosity, which does not mean they would consume it regularly for varied reasons. Therefore, the acceptability of ‘CBM’ is often overestimated because it is based on willingness to try, and not on intentions to eat ‘CBM’ regularly. Many surveys confirm that respondents who express a high acceptance tend to be young, urban, and highly educated at least in some major countries but not all, possess little factual knowledge about ‘CBM’ production, and are already inclined to reduce meat consumption (for a variety of reasons including concerns about animal welfare and environmental issues). Conversely, older, and less urban consumers are more reluctant and express concerns about the future of the countryside, livestock farming, and landscape and pastures. Such consumers also highlight the unnaturalness and low healthiness of the product and express a higher emotional resistance. In any case, willingness to pay is low overall, since most respondents (68% in France, 71% in Brazil, and 86% in China) were willing to pay less for ‘CBM’ compared to conventional meat (Ellies-Oury et al., 2022). All these motives and barriers may differ from country to country with barriers being stronger in those regions holding stronger traditional values and motives being stronger where the challenges related to food demand are the greatest, such as in Asia and Africa. Conclusions “Cellular agriculture”, including ‘CBM’ and precision fermentation, has been promoted as an alternative for producing future food proteins by replacing dairy and meat without involving animals. The development of such novel technologies, despite several ethical concerns, is accompanied by a multitude of research reports, the creation of start-ups, massive investments, and prominent media coverage. It has evolved into a hot topic for societal debates, often associated with divergent opinions. Currently, however, these new food products are not available for consumption in meaningful amounts, nor are they exposed to independent evaluation on economic or scientific grounds. Indeed, the multitude of technical challenges related to the scalability and production of ‘CBM’ prototypes are not available for accurate and independent assessment in terms of their sustainability, intrinsic (sensory, nutritional, and technological attributes) or extrinsic quality. The perception of unnaturalness and the low or poor cultural acceptance by consumers, mainly because of lack of familiarity and uncertainties about the aesthetics, are other barriers to societal acceptance. Therefore, they are well perceived only by a certain category of people (niche market or animal activist groups). The other drawbacks of these products are the limited data on the long-term human health implications (safety and health), environmental impact (although they claim less land usage), and obscure risks related with cellular engineering. Streamlined regulatory measures and continued basic research, free of conflicts of interest, are necessary to fuel product innovation, set forth requirements for appropriate monitoring of these innovative technologies, and to promote such novel foods while simultaneously ensuring both consumer safety/acceptability and guaranteeing low environmental impact. Finally, we believe that the need for more proteins to feed the world’s growing population will continue to be the main driver of innovation in the production of proteins and meat alternatives. We must keep in mind, however, that most of the growth in population will be in developing countries. Thus, major challenges that need to be further considered in the development of such novel foods from “cellular agriculture” origin will be their price and distribution logistics as well as how they are situated in a fair and affordable food equity framework.

Implications Agricultural land is a scarce resource globally and will continue to encounter challenges to sustainably increase food production in the face of global change. Adaptations that make use of livestock should ideally incorporate agroecological principles (e.g., improved circularity), while limiting feed-food competition. However, they should also remain respectful of the diversity of ecosystem contexts, availability of resources, and the various social and economic needs of local populations. Herbivores are a natural constituent of the world’s ecosystems and have played a key role in the last several million years. As the numbers of wild herbivores have greatly decreased, largely due to human action, the maintenance of such roles depends on the practice of adequate livestock management. This is the ecological basis for sustainable livestock. Well-managed animals function as an integral and productive part of agricultural systems. Among other outcomes, they can convert massive quantities of nonedible biomass (inevitably arising from pasture systems and from growing plants into human food), recycle plant nutrients back to the land, sequester carbon, improve soil health, and offer many ecosystem services. To optimize both environmental impact and food supply, the broad and underutilized diversity that is inherent to livestock systems should be mobilized instead of being suppressed. This diversity can, for instance, be observed in terms of species and breeds, but also in terms of production methods and management strategies. Introduction The animal production sector is facing important challenges in the context of global change. This is especially related to population growth, land erosion, a decrease in biodiversity, wastage of water, depletion of resources, disruption of nutrient cycles and eutrophication, and climate change. Even if livestock agriculture has contributed to these problems, as have other forms of human productivity, it can contribute to the solution, provided it operates within an agroecological framework and environmental boundaries, while still respecting primordial principles of diversity (Leroy et al., 2022). The latter relates not only to the biological variety of livestock options as such, but also to the important heterogeneity within ecosystem types, production and management methods, and local needs and resources. Indeed, livestock products and production systems differ, from intensive to extensive, from arctic to tropical, from highly technological to indigenous, or from being a by-product to being the main focus of the system. Definitions vary, but there are >40 farmed animal species and >7,000 breeds adaptive to specific local needs and context (FAO, 2021). They produce a vast range of foods and services for humans, from diets that are largely inedible for humans. Only a small share of this bounty of diversity is utilized to its full potential, which makes it a valuable resource pool for solutions (UNFSS, 2021). Turning that biological diversity to the ecological context in which the animals are deployed, combined with a proper set of adapted management strategies, will be of utmost importance. In addition, various innovations have the potential to further open new solution spaces, as is the case for precision livestock farming, genetics, feed, robotics, environmental monitoring, and business models (UNFSS, 2021). Livestock can already provide almost half of our global protein requirements while staying within key planetary boundaries (Van Zanten et al., 2018), and more innovation will increase this share even further (Mottet et al., 2018). But besides bringing in protein of higher quality than when derived from plants, animal-source foods also contain highly bioavailable micronutrients that are often difficult to obtain from crops (see elsewhere in this Special Issue; Leroy et al., 2023). Below, we will outline the importance of 1) the variability of the ecological context in which livestock systems operate, and how this can both constrain and stimulate the potential of animal production, 2) the need to factor in agro-ecological principles, such as improved circularity and minimized feed-food competition, and 3) the positive ecosystem contributions of well-managed livestock and how these are affected by management strategies. The Importance of Ecological 
Context and Diversity The role of livestock in the world’s terrestrial ecosystems has been negatively impacted by the dominant views on “Nature” as landscapes predominantly devoid of human influence (Bond, 2019). As a result, many environmentalists are advocating for an intensification of human activities in ecosystems that have been heavily modified, while completely abandoning human activities in lands suitable for ecological restoration – the so-called “land sparing” approach. Such an approach naturally promotes the abandonment of vast lands used by sustainable livestock management, as they are typically considered to have low production potential and high biodiversity and ecosystem functionality. In recent decades, however, substantial evidence from specialized fields is contesting such views (Manzano-Baena and Salguero-Herrera, 2018). All continents, except for Antarctica, have been significantly affected by human activities. These regions hosted a significant amount of megafauna, which became extinct outside Africa and South Asia only some thousands of years ago. Naïve animals, not used to people, were easy prey for humans expanding beyond their previous range, which added to technological advances in hunting and climate fluctuations. These extinctions would have had a more dramatic effect on ecosystems than what we see today. But the human activities that followed had a similar action as herbivores on landscapes, namely through the use of fire. Evidence from Africa shows how megafauna kept landscapes open by efficiently consuming massive quantities of vegetation, especially by seasonal migrations that follow the peaks in plant productivity. These seasonal migrations achieve herbivore densities that are well above the ones observed in temperate protected areas, constrained by surrounding human development. Large herbivore migrations are also assumed to have facilitated the formation of deep organic soils that are now used by some of the most productive crop production systems worldwide. Moreover, elephants are known to tumble down trees and have a particularly important influence in keeping woody vegetation at bay. According to data from national parks where herbivore migrations are still possible, current baseline levels of herbivore densities in Africa are large – and often equivalent to livestock densities under local ranching practices. Such high herbivore levels typified many other parts of the world before the megafauna disappeared, but livestock has kept a high herbivore pressure in the ecosystems (Manzano et al., 2023a). In these contexts, the reduction of ruminants leads to the invasion of deep tap rooted woody species that have deleterious effects on ecological function. Hunter-gatherers use fires to contain woody vegetation and promote grassy biomass, increasing the productivity of the ecosystem and the availability of prey. Pastoralists also use fire to increase fodder availability for livestock, while targeted specialized management utilizes animals such as goats to contain and even revert shrub spread, whereas livestock mobility achieves a high degree of efficiency in plant matter use. Their movement allows them to follow plant growth across vast landscapes, and it thereby also increases the quality of fresh forage intake. The resulting landscapes (Figure 1) of all three scenarios – shaped by either megafauna, hunter-gatherers, or livestock keepers – achieves a similar landscape structure of mixed tree groves, shrubs, and open pasture that, except for rainforests, has dominated the planet’s surface since the late Miocene, 12 million years ago. With most plants and dependent animals exposed under the sun during this entire time, biodiversity has adapted to it. Many plant species in biodiverse pastures require considerable amounts of light to survive (Eskelinen et al., 2022), and depend on ecological processes that disturb and contain closed-canopy vegetation. Figure 1. Images of Open Ecosystems (Bond, 2019) dominated by wild herbivores (top left: Cabañeros National Park, Spain; bottom left: Maasai Mara conservancies, Kenya), and of cultural landscapes displaying a similar vegetation structure but that are dominated by domestic herbivores (top right: Conquense Drove Road at Almagro, Spain; bottom right: dehesa in Cordoba municipality, Spain). Pictures’ author: Pablo Manzano. Megafauna is no longer available in Central European, Eastern North American, or East Asian landscapes, so that their abandonment leads to biodiversity losses and the collapse of some high nature value ecosystems, as has been observed in southern Fennoscandia. Once open ecosystems are assumed to be natural (Figure 2), the introduction of extant African and South Asian megafaunal species could be considered as an ecological restoration strategy. But this is no longer viable in contemporary societies because of landscape fragmentation, the presence of infrastructures that render migration impossible, and the high costs of human-wildlife conflict. With adequate management, however, livestock production can provide these important ecosystem services, even if constrained by impacts of human development on the landscape. The necessity of sustainable productive activities to maintain important ecosystem processes, supported by increasing evidence from ecological science (Plieninger et al., 2014; Manzano-Baena and Salguero-Herrera, 2018), reinforces the alternative “land sharing” approach previously advocated for by rural development, human rights, and Indigenous peoples’ advocates. Figure 2. Map of conventionally assumed biomes, defined either as treeless areas or closed canopy forests (Olson et al., 2001), with overlapping areas that display alternative stable states, otherwise defined as Open Ecosystems (Bond, 2019). Map source: Manzano et al. (2023a). The Need to Factor in Agroecology, Circularity, and Feed-food Competition Traditionally, livestock systems were used to create nutrient rich-food from low opportunity cost feed material. Ruminants were tasked to create food from inedible fodder, whereas monogastrics were fed undesired by-products, such as the residues of potatoes or other types of food-waste. High-productivity livestock systems, however, are increasingly reliant on additional support from feed crops grown on arable land, which engenders feed-food competition (Mottet et al., 2017). The agroecological potential of livestock primarily relates to the fact that they are able to upcycle copious quantities of nonedible biomass into nutritious foods, while also recycling plant nutrients back to the land, improving soil health, and sequestering carbon (see the next section, below). As such, they are intrinsically connected to sustainable crop agriculture. The purpose of the latter is to generate biomass from plants, of which only a part is suitable for harvest and subsequent production of human food. Even if agricultural innovations have massively increased the volume of biomass produced annually, as well as its subfractions suitable for harvest, most of this output is still nonedible and must ideally be recirculated in view of soil fertility (where animals come in as helpful). Cultivation of wheat and corn, for instance, is highly efficient in the generation of material for harvest compared to nonedible aboveground biomass (e.g., straw), but the ratio remains at 1:1. Other plants cultures show even higher proportions of nonedible biomass (legume seeds, up to 2:1; rape seed, 3:1; sunflower, 4:1). In addition, considerable amounts of nonedible biomass are generated as by-products during food processing, of which the proportion of total inputs ranges between 20% (e.g., intensive milling) and 60% (e.g., production of rape seed oil). While such by-products may still contain human-edible subfractions, they are usually discarded because of technological or economic reasons. Further nonedible biomass arises from inclusion of “green fertilizers” (e.g., use of clover-grass mixtures or alfalfa into the crop rotation systems of organic farming). This practice increases soil fertility but also blocks cultivation of crops at least every fifth year, hence increasing the direct nonedible biomass from arable land by 20% at the expense of human edible food production. Whereas monogastric animals are particularly useful for the efficient conversion of human-inedible by-products from crops, ruminants also have the capacity to make use of grasslands. The latter not only provides a vast source of nonedible biomass but can often also not be converted into arable land (e.g., due to topographical or climatic reasons). Pasture-based production systems, such as grass-fed beef and dairy cattle, thus convert an inedible material for humans into a consumable form of protein. Often this land is unsuitable for arable farming and therefore this form of meat and milk production has no opportunity for direct food production through cropping. Globally, grasslands represent 70% of the total agricultural area, but even in areas with intensive arable farming, considerable proportions of grasslands can be found (e.g., 30% in Germany). Summing up arable land and grassland, the ratio of nonhuman edible to human-edible biomass accounts for at least 3:1, provided that no green fertilizers nor other green biomass for feeding purposes is grown on arable land. The ratio observed in practice is at least 4:1 in areas where intensive arable farming is practiced (Wirsenius, 2000; GOALSciences, 2022). Globally, the fact that animals utilize forage and crop residues fits the estimate that 86% of global livestock feed does not compete with human food (Mottet et al., 2017). Obviously, there is still room for improvement within the remaining 14%, in view of further reductions of food-feed competition. It needs to be considered, however, that even for the human-edible part of the feed, animals can function as a buffer for surpluses or for crops that are in principle edible but have been discarded because they did not sufficiently meet quality standards. Circularity of inevitably occurring, nonedible biomass, and the plant nutrients bound therein (nitrogen, phosphorus) is essential to maintain fertility of agricultural areas. Unless they are left to rot (with often negative consequences on the ecosystem), this may be achieved only through conversion of nonedible biomass into storable organic fertilizers and targeted application to the plants. Two conversion routes are feasible: fermentation in biogas plants ending up in biogas residues or feeding to livestock producing human food as well as manure which is recycled back onto the cropped area in most cases. It is only through livestock that the provision of organic fertilizers will also generate the additional bonus of high-quality human food. Based on the ecological rationale of circularity, corresponding emissions cannot be attributed to livestock production only. They would also be generated by the inevitably occurring nonedible biomass that would be either left to rot or would be routed to biogas production instead, when not fed to livestock. The same applies to arable land, water, energy, etc., that was consumed during generation of the edible counterpart of the nonedible biomass. Methane released by ruminants during digestion of nonedible feed materials makes a specific difference to the other two pathways of recirculation. Since atmospheric methane is quickly degraded to CO2, its long-term effect on global warming is limited, provided ruminant numbers (or their total methane emissions) do not increase (see elsewhere in this Special Issue; Manzano et al., 2023b). On the other hand, conversion of inevitably occurring, nonedible biomass to high quality human food runs without food competition and is most efficient with ruminants. Taken together, inclusion of livestock into agricultural systems is an efficient driver of circularity. Removing livestock from the system would dissipate the generation of human food from nonedible biomass. Such a system would significantly expand the consumption of resources (land, water, energy) as well as of emissions per nutritional unit (kilocalories, protein, etc.) (van Zanten et al., 2018). Indeed, current high-productivity livestock systems are reliant on intensive production of feed on arable land, thereby charging the environment and climate. But these unfavorable consequences of how intensive livestock production is currently managed, do not justify complete abstinence from livestock. The minimum impact of agricultural production of human food on environment and climate may be found in mixed systems, where livestock production is based on inevitably occurring, nonedible biomass. More circular systems will likely result in smaller and more diverse herd sizes and potentially also a lower output of animal-source foods, even though the latter comes with large uncertainty because some pastoral and agroecological management systems can be remarkably productive (cf., the relatively high stocking rates needed for adaptive grazing). Key to this philosophy is placing livestock where it is most appropriate from a climate, system, and management perspective, thus having an impact on all sustainability indicators. Positive Ecosystem Contributions of 
Well-managed Livestock and the Link 
with Management Today, much of the discussion on the impact of livestock on the environment commonly focuses on the production of methane, via reticulo-rumen fermentation from ruminant species, leading to a myopic approach to improving the environmental impact of food production. However, the positive impact of livestock on other ecosystem services and as tools to manage and improve the land we rely on for food production can often get overlooked or minimized. One such regulating service is livestock’s impact on soil health and carbon sequestration, particularly in soils that have a legacy of mismanagement. Soil carbon sequestration from livestock production is commonly left out of the greenhouse gas assessments, but in a review of the literature, Cusack et al. (2021) identified soil carbon sequestration as having the largest potential to reduce beef emissions globally, both per unit of product and per unit of land. The potential for carbon sequestration comes via two key mechanisms: 1) restoration of degraded landscapes through the introduction of livestock, and 2) use of adaptive grazing to improve ecological function (Rowntree et al., 2020; Sanderson et al., 2020; Teague and Kreuter, 2020; Grandin, 2022). Landscape restoration is of particular importance today, considering the legacy of mismanagement found in most soils under agricultural management across the globe (Lal, 2003). These soil losses have occurred primarily in cropping systems and due to overgrazing. Sanderman et al. (2017) estimated that 133 Pg (Petagram) of carbon has been lost in the top 2 m of soil globally due to agriculture. Current and historical farming and ranching practices have aided in this loss of soil carbon due to its growing reliance in past decades on simple annual crop rotations, synthetic inputs, and extractive practices (Lal, 2004). As a result of these practices, soil health and quality have been reduced, along with agricultural outputs from those landscapes. In addition, farmers/ranchers’ reliance on external inputs has increased to keep their operations productive. However, research has indicated that through the introduction of perennial forages, reducing tillage and incorporating livestock, soil carbon can be restored, and overall ecosystem function improved 
(Lal, 2004; Rowntree et al., 2020; Teague and Kreuter, 2020). This loss/sequestration of carbon is rarely associated and counted when crop products are compared to livestock systems. Adaptive grazing management is a nonprescriptive outcome-based approach to grazing management that aims at keeping soil covered, thereby minimizing disturbance (including via overgrazing), minimizing synthetic inputs, and increasing plant diversity. Additionally, management is typically centered on appropriate timing of short-duration, high-intensity grazing events, meanwhile leaving adequate plant residue for plant recovery. The impetus of this management style more closely mimics the natural behavior of grazing animals across landscapes where sporadic, but concentrated and uniform forage utilization is typical. By doing so, plants are allowed adequate time to recover between grazing events, keeping them and their root systems healthy. Additionally, this maintains plants in an active state of regrowth longer, increases solar energy capture, and aids in the cycling of above ground nutrients back into the soil via the physical trampling of plant material and through urine and fecal deposition. Implementation of such management has been observed in numerous studies to improve soil health and water holding capacity, reduce external input requirements, increase soil carbon sequestration, and partially offset the environmental impact of production, amongst numerous other benefits (Teague et al., 2011; Machmuller et al., 2015; Rowntree et al., 2020). As important as carbon sequestration in grass and rangelands is for the mitigation of environmental damage, it is also paramount that the protection of the carbon that is already stored is safeguarded and that natural ecosystems are kept intact. Globally, permanent grass and rangelands are under threat of conversion into marginal cropping systems or other land uses. In the United States, fueled by ethanol incentives, approximately 3 million ha of grass and rangeland was converted to cropping systems between 2008 and 2012, with the USDA estimating that 960,000 ha of rangeland alone was lost between 2007 and 2015 (Lark et al., 2015; USDA, 2018). These grass and rangelands provide numerous ecosystem services, including wildlife habitat, recreation, and food production, to name a few, and they are often considered to be at a long-term equilibrium for soil carbon (when healthy). Their soils play a critical role in the regulation of global carbon cycling through long-term carbon storage. It is estimated that, globally, grassland and rangeland soils store approximately 20% of soil organic carbon (Conant, 2012). In these arid and semi-arid environments, a key driver to the loss of soil carbon is disturbance from tillage, overgrazing, or urban expansion. This land conversion serves as a significant carbon source to the atmosphere, along with increasing soil and other nutrient losses (Spawn et al., 2019; Zhang et al., 2021). In the United States, Spawn et al. (2019) estimated that cropland expansion into grasslands resulted in a 38.8 MMTC (million metric tons of CO2) yr−1 emitted from 2008 to 2012. Similar annual emissions were observed by Yu et al. (2019) from 1980 to 2016. Furthermore, Zhang et al. (2021) simulated the conversion of grassland to crop production in the Midwestern United States and estimated that soil erosion was increased by ~8% annually, and that nitrogen loss increased by ~4%. These losses have impacts beyond anthropogenic emissions, such as sedimentation and eutrophication of waterways that reduce water quality for humans and aquatic ecosystems. The new cropland produced from the land conversion is, typically, of marginal quality as well. The new cropland has a yield deficit of 6.5% of the United States average and has negative impacts on plant and animal biodiversity (Lark et al., 2015). Therefore, while some of these soils may have saturated soil organic carbon stocks, management that protects against degradation/conversion provides significant value by producing high-quality, nutritious human-edible products, protecting the stored carbon from being lost, and protecting natural ecosystems. Conclusion Environmental protection of ecological resources and commercial livestock management are not a contradiction. On the contrary, the one necessitates the other. Commercial livestock management depends on the sustainable provision of ecological resources of water, biodiversity, feeding grounds, and crop land production. At the same time, except for the very few remaining untouched wilderness areas of the world, ecological management towards environmental protection of these resources requires active human management. Livestock are an indispensable instrument in such management to create and sustain the multiple circular flow of materials in the soils, water bodies, and atmosphere.