Circular bioeconomy: animal by-products from livestock carcass processing

Livestock carcass production systems (as opposed to dairy and egg production) have as their primary objective to produce meat for human consumption. This production is accompanied by by-products, which are either not consumable by humans or not appreciated (e.g., offals in certain regions). By-products from meat production contain valuable components (e.g., protein, fat, minerals), which may be used by or recycled either directly to humans or in livestock feed, following specific processes (called rendering). Rendered animal by-products can be used to replace other sources of nutrients such as plant-based proteins (e.g., soybean meal), calcium and phosphorus sources (mined sources), fat (e.g., oil from oilseed), maintaining these nutrients within the food chain and improving sustainability via circularity. Advancements in the rendering sector resulting from the Bovine Spongiform Encephalopathy (BSE) crisis have allowed for the safe use of these by-products. However, a higher use of these valuable by-products is required in the context of circular bioeconomy. The concept of valorization of Animal By-Products (ABP) follows the principle of the ‘Food Waste Hierarchy’ and ‘Value Pyramid’ described by Al Zohairi et al. (2023, Figure 1). Sometimes these concepts are described as a ‘cascading use of biomass’ (Dubois and Gomez San Juan, 2016). The preferred option is source prevention (i.e., avoiding generation of food waste), followed by food recovery where a greater proportion of the animal biomass is used or recovered as human edible food. After food recovery, the value pyramid proposes recycling by-products to produce high-value chemicals and pharmaceutical products, then feed and subsequently food via livestock or social value via pet food, followed by recovery for industrial applications. The latter can include the production of a range of lower value chemicals, and materials such as fertilizers, soap, or biodiesel. The ABP can also be used as a substrate for biodigestion or combusted to produce bioenergy. Finally, when all other options have been exhausted, the remaining ABP can be disposed of through combustion or landfilling. Animal products from abattoirs hierarchy and value pyramid. Source: (Al-Zohairi, Knudsen, and Mogensen, 2023). Animal-sourced foods are important components of a balanced human diet (Ahmad, Imran, and Hussain, 2018), providing: - Highly digestible sources of protein (i.e., bioavailable and balanced in essential amino acids). - High quality (long chain) essential fatty acids (i.e., omega-3 and omega-6). - Micronutrients, highly bioavailable minerals (e.g., haem iron) and vitamins (including hard-to-source B-vitamins, e.g., B12). Further to the production of animal-sourced food, livestock production systems also provide ecosystem services, manure for fertilization, and multiple by-products with potential to produce a wide range of human edible products, animal feeds, bioenergy, or for higher value uses such as pharmaceuticals, and cosmetics (Wilkinson and Meeker, 2021). In essence, the farming of livestock results in various products that leave the farm for further processing. These include live animals for slaughter and production of meat and offal and their co-products, such as milk, fiber (e.g., wool, mohair, camel hair), and eggs. This paper focuses on the range of by-products from livestock carcasses via rendering and subsequent potential in a circular bioeconomy. Livestock is processed for edible products (meat and offal), but there are also multiple other by-products, residuals, and wastes with the potential to generate alternative products (Figure 2). Redirection of these products towards alternative uses and away from waste streams is a key component of achieving circularity, while in concert considering their safety. Rendering is an important step in livestock processing, as it enables animals that have not been approved for livestock processing for human consumption (e.g., livestock failing inspection of carcass or carcass quality imperfection) or human inedible products (e.g., bones, feathers) from abattoirs to be upcycled into a range of safe and valuable by-products (Wilkinson and Meeker, 2021; Figure 2). For example, paunch (i.e., gastrointestinal content) from abattoirs is predominantly used as a source of energy in abattoirs (Karlis, Prescicce, Giner Santonja, Brinkmann, and Roudier, 2024) or to generate compost as a fertilizer. Description of multiple co-products, residues generated from abattoirs and rendering plants, illustrating various options for upcycling and increased circularity. Source: Scientific Advisory Panel, World Renderers Organization, 2023. In dark blue, source of the products and co-products, in light blue, high value products, in light green, by-products, and in dark green and upper case, processes. An array of high-value ABP (supporting the principle of the value pyramid, Figure 1) are produced for applications in biobased industries, such as food, pharmaceutical, and cosmetic industries (e.g., heparin, glucosamine, gelatin, chondroitin; Table 1; Toldrà et al., 2021). Pharmaceutical grade blood collection is common in abattoirs for plasma or serum. One company in New Zealand uses over two (2) million liters of blood, which is extracted for blood products including serum for cell culture and biomedical purposes, as well as bovine serum albumin (e.g., used as transport carrier for various drugs) and pro-thrombin (i.e., for controlling blood coagulation). In 2022, exports of blood products and glands from processed cattle and sheep returned over US$130 million or the equivalent of over 2% of the total returns in New Zealand beef and sheep meat (MIA, 2022). This collection and processing of blood into high-value pharmaceutical products is an example of upcycling to the top of the value pyramid (Figure 1). Similarly, heparin is a widely used pharmaceutical anticoagulant for preventing blood clotting in medical procedures, which is derived from the mucosal tissue of livestock, particularly pig intestines (Middeldorp, 2008). Innovative and new green extractive techniques have been developed for further extraction of important molecules in co-products of the rendering industry such as pulse electric, microwave, extrusion, or ultrasound assisted extraction, high hydrostatic pressure extraction, supercritical fluid extraction, pressurize liquid extraction, subcritical liquid extraction, membrane separation technologies, fermentation and enzymatic extraction (Bruno, Anta Akouan Ekorong, Karlal, Catherine, and Kudre, 2019). A summary of the main high-value animal-based products A summary of the main high-value animal-based products As described in Figure 2, the slaughtering of livestock leads to a large variety of products, some of them consumed as food by humans, while others (co-products) may provide valuable materials, such as nutraceuticals, clothing, and building materials (e.g., insulation) and be used by biobased industries. Some residues of meat production and of the biobased industries that are unsuitable for human consumption can be upscaled by rendering (in green boxes). In Europe and North America (United States of America and Canada), about 49.5 million tons of by-products and residues are produced by abattoirs, mostly from non-edible parts of the carcass rather than other causes (e.g., fallen stock or condemned carcasses). Variations exist between various countries on the type of co-products, as global consumers may have different consumption models, e.g., in Europe, offal and blood are not largely consumed, in contrast to Asia or Africa. Thus, the use of co-products may be different between countries. This necessitates having a local evaluation of the resources and their potential use. Protein (and bones) meal and rendered fats are the two (2) key ingredients produced through rendering processes. In line with the hierarchy and value pyramid (Figure 1), the preferred use of rendered product should be in livestock feed to keep the nutrients included in these products within the food chain, while ensuring the safety of the food chain. Further upcycling may be produced with the remaining volume. Dietary protein is a vital component of any animal feed as it supports bodily functions, growth, muscle development, and other production processes (e.g., milk and eggs). It is also the costliest component of the ration, financially and often environmentally (Azarkamand et al., 2024). Currently, soybean meal is the most common non-forage protein source fed to livestock, depending on market conditions and availability. More sustainable circular protein sources are critically needed. Protein meals from rendered ABP represent a potentially valuable source of protein with digestibility between 75% and 94% and a high biological value (up to 8.7% lysine and 1.4% methionine), depending on the sourced meal (INRAE CIRAD AFZ and FAO, 2025). Research indicates that many of these sources could be substituted for soybean meal in the diet of pigs, poultry, and aquaculture. Protein meal can account for 5% to 25% of the diets of poultry and pigs, supplying one third of the dietary protein (Leiva et al., 2018). Studies with pigs, where soybean meal was replaced by protein meal, have had variable responses. (Shelton et al., 2001) reported lower performance of growing finishing pigs offered protein meal as compared with soybean meal. In contrast, (Gottlob et al., 2004) reported improved pigs’ average daily gain when protein meal constituted up to 5% of the diet, with it performing as well as soybean meal at higher incorporation rates. In poultry, the replacement of soybean meal and dicalcium phosphate with protein meal at 2%, 4%, or 6% had no effect on egg mass (i.e., more eggs with lower weight) and no change in feed conversion rate, body weight, or mortality (Bozkurt, Alçiçek, and Cabuk, 2004). In aquaculture, the suitability of protein meal to replace soybean meal has also been exemplified in a range of fish species (Trachinotos carolinus L. [Rossi and Davis, 2014]; Spraus aurata [Moutinho et al., 2017]; Ictalurus punctatu [Mohsen and Lovell, 1990]). However, due to the nature of protein meal production, its composition, quality, and nutritional value as a sustainable feed ingredient are related to the nature of the material from which it is derived (Hendriks et al., 2002). In addition, the level of protein meal incorporated in livestock diets may also be limited by its mineral content. Solà-Oriol, Roura, and Torrallardona (2011) reported that feeds with 5% protein meal were preferred over soybean meal by pigs. However, values greater than 5% reduced feed intake, probably due to the high mineral content. Dietary minerals (especially calcium and phosphorus) are important for skeletal development, milk composition, and eggshell production. Currently, mined phosphate rock and limestone are used as sources of phosphorus and calcium, but protein meals and bone meals are also sources of highly digestible calcium and phosphorus. Bozkurt et al. (2004) showed that egg quality (specific gravity and Haugh unit) and eggshell integrity (less cracked–broken eggs) were improved when protein meal replaced dicalcium phosphate in the diet of layers. As a provider of high-quality protein, vitamins, and minerals, protein meal is a vital ingredient in pet foods, which cannot be easily replaced by plant-based proteins. This is especially true for cats as carnivores that have a specific requirement for taurine, which is lacking in all plant-based protein. In addition to their nutritional value, protein meals have been shown to improve the palatability of pet foods (Boskot, 2009). Rendered fats are also a vital ingredient in feed, as well as for the food sector, as depending on the production system, they may offset environmental impacts caused by the growth of the palm and soybean oil industries. Palm oil replaced rendered fats in many food items in response to human health concerns (C16:0 and C18:0). However, it has been shown that C16:0, which is in higher concentration in palm oil than rendered fats, raises LDL cholesterol, whereas C18:0 (i.e., predominantly saturated fatty acids in rendered fats), does not raise LDL cholesterol, possibly due to its rapid conversion to oleic acid in the body (Grundy, 2013). With growing interest and financial returns in the pet market, ABP are also being included as a functional ingredient in pet foods either as a nutraceutical (Table 1) or to improve digestibility (e.g., pancreatin, extracted from pigs’ pancreases (Bampidis et al. 2023). In addition, other ABP are used as pet treats, such as pigs’ ears, raw hide, and bones (Martinez-Alvarez, Chamorro, and Brenes, 2015). Bovine Spongiform Encephalopathy (BSE), a fatal neurodegenerative disease in cattle caused by prions, was first identified in the United Kingdom in the 1980s and rapidly spread due to the use of infected ruminant-derived meat and bone meal in cattle feed. Woodgate and Wilkinson (2021) described how changes in the rendering sector in the 1980s, driven by economics, resulted in a failure to deactivate the causative prion proteins associated with transmissible spongiform encephalopathies (e.g., BSE, scrapie, Creutzfeld-Jacob disease). Subsequent transmissible spongiform encephalopathy deactivation trials showed that a traditional rendering system, including a hyperbaric pressure stage (three bars for 20 minutes), resulted in the inactivation of transmissible spongiform encephalopathy to below detectable levels (Woodgate and Wilkinson, 2021). The emergence of BSE led European countries to restrict the use of specified risk materials, including all protein meal products from all livestock species for use in feed (Woodgate and Wilkinson, 2021), to further the BSE the World of Animal to to the disease that on avoiding cattle being fed with protein meals the of these reduced the of BSE to of BSE the rendered products, the are should not be fed ruminant-derived protein meals to bovine with a of are and feed in rendering and feed are to avoiding of bovine feed with ruminant-derived protein be in to that ruminant-derived protein is not into bovine feed. and risk countries are on their BSE no or in or in for than or The European a to the spread of BSE, a for ABP into risk (Table 2). 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