Introduction
Growing meat in a lab for pet food from animal stem cells has many potential benefits including avoidance of legumes or animal by-products as sources of protein and providing a sustainable production of meat for cats and dogs. However, could this production of cell-cultured meat (also known as lab-grown meat and in vitro meat) provide meat for pets that is nutritionally sustainable? Nutritional sustainability is “the ability of a food system to provide sufficient energy and the amounts of essential nutrients required to maintain good health in a population without compromising the ability of future generations”.20 Okin (2017) calculated that dogs and cats in the United States consume as much dietary energy as ~62 million Americans (approximately one-fifth of the US population). With more pet owners feeding their pets premium pet food products containing more animal products that are considered edible for humans, there is concern over the sustainability of these ingredients for pet food.16,20 Theoretically, a single farm animal may be used to produce the world’s meat supply2 and, cell-cultured meat could be a nutritionally sustainable ingredient for pet food if it provides the nutrients cats and dogs require to maintain good health.
Animal tissues from chicken, turkey, fish, beef and lamb and viscera such as livers, lungs and spleens are common pet food ingredients that have high-protein concentrations.9 Besides having a high protein content with essential amino acids, conventional meat (meat from slaughtered animals) is also a source of vitamins and minerals.9,24 For cell-cultured meat products to be competitive in the pet food industry it must meet or exceed the nutritional value of conventional meat.11 The production methods and technologies used in creating cell-cultured meat (Figure 1) will have an impact on the nutritional value of pet food.25
Figure 1. Components involved in producing cell-cultured meat (adapted from Specht (2018))
Regulatory Framework
Human food products derived from cells of livestock and poultry will be jointly overseen by the U.S. Department of Agriculture’s (USDA) Food Safety and Inspection Service (FSIS) and Food and Drug Administration (FDA). FDA oversees cell collection, cell banks, and cell growth and differentiation, whereas FSIS will oversee the production and labeling of human food products derived from the cells of livestock and poultry.21 This decision will impact the regulatory pathway for cell-culture meat in pet food.22 The agencies may need to write regulatory language to clarify that lab-grown meat for pet food is new, but it is still “meat” under the law, falling under the purview of the USDA through its Federal Meat Inspection Act Authority.13 Laboratories would then need to comply with inspection requirements under 21 U.S.C. §606(a), storage requirements under 21 U.S.C. §624, sanitation requirements under 21 U.S.C. §608, as well as regulatory requirements under 9 CFR Chapter III, Subchapter E.13 It is also important to keep in mind that substances including ingredients added to the cell culture media (e.g., minerals, vitamins or other nutrients) that are reasonably expected to become a component of food must be generally recognized as safe (GRAS) for an intended use (21 CFR 582 and 584) or must have approval as food additives (21 CFR 570, 571 and 573), and colorings must have approvals for that use as specified in 21 CFR 70 and be listed in Parts 73, 74, or 81 for it to be allowed in pet food products.7
“Complete & balanced” pet food
If the nutritional adequacy statement on the pet food product includes the phrase “complete and balanced,” then the product is intended to be fed as a pet’s sole diet and is nutritionally balanced.6 In order to have “complete and balanced” in the nutritional adequacy statement, a dog or cat food must either: (1) meet one of the Association of American Feed Control Officials (AAFCO) Dog or Cat Food Nutrient Profiles; or (2) successfully complete a feeding trial using AAFCO procedures.6 Table 1 shows the nutrients required in a “complete and balanced” pet food product; therefore, a pet food product which contains cell-cultured meat must have those nutrients and meet the requirements set forth by AAFCO in to order to be considered nutritionally balanced and intended to be fed as a pet’s sole diet.
The biological needs of specific cell types, such as muscle cells, are similar regardless of the species of origin across the animal species; therefore, a company that can produce minced chicken for cat food might be able to produce minced turkey cat food with relatively little adaptation.19 However, arguably more important than the type of animal species from which the cells are derived (i.e., the protein source) are the levels, ratios and bioavailability (i.e., available for absorption and utilization) of amino acids in the final product (i.e., the pet food).23 Different protein sources contribute to different amino acid content, thus influencing secondary and tertiary structure, which is reflected in bioavailability (Table 2). However, the overall nutritional levels and ratios of the various amino acids in pet food will determine the effectiveness of the product in providing a well-balanced diet for canines and felines.
CS= chemical score; BV=biological value; NPU=net protein utilization; PER=protein efficiency ratio
* Feedstuffs Ingredient Analysis Table: 1996 Edition. (As is basis.)
** (NRC, 1974; Robinson, 1987; Jurgens, 1988; Brody, 1994)
It is also important to keep in mind that a high crude protein content does not always equal high quality protein. For example, crude protein content is typically calculated from the nitrogen content by the Kjeldahl method or Dumas combustion procedure;9 as melamine is high in nitrogen such tests will interpret this nitrogen content as protein. Melamine in pet-food lead to the death of hundreds of cats and dogs in the USA back in 2007 (FAO, 2008). To achieve high-quality protein in food, protein sources are often combined based on their amino acid excesses and deficiencies so that the nutritional weaknesses of each source will be counterbalanced by the strengths of other sources.9 Therefore, an option for improving the protein quality of cell-culture meat in pet foods would be creating cell-cultured meat that complements other protein sources, potentially combining different cell-cultured meats. Another option for a balanced amino acid source is amino acid fortification wherein one or more individual amino acid types can be added to a food when the main protein source of the food may be lacking.9 According to Lodish et al. (2000), histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine must be supplied in the cell-culture media because it cannot by synthesized by adult vertebrate animals. Most cultured cells also require cysteine, glutamine, and tyrosine added to the cell culture media because these amino acids are synthesized by specialized cells; for instance, liver cells make tyrosine from phenylalanine.12 Therefore, various amino acids could potentially be added to the cell-culture media for a custom formulation (Figure 1) or to the end product to achieve the final desired balance of amino acids.
Adipocyte cells (fat cells) provides lipids for meat and is an important nutrient for pets (Table 1). In a two-dimensional layer, adipocyte cells could be grown in a separate culture then added to the cultured muscles; or cells could be seeded onto a scaffolding material that provides a physical support as the cells differentiate and mature into the desired cell types including adipocyte cells.19 With cell-culturing, it is also possible to manipulate the composition of the culture medium to influence the fatty acid composition and consequently, the flavor of the cultured meat.2
There are 23 and 26 essential minerals, vitamins and vitamin-like substances for dogs and cats, respectively (Table 1). Usually, vitamins and minerals are provided to pet food via a prepared “packet” called premix or through the protein source. Vitamins that are usually added to pet food though a “premix” could potentially be added through the cell culture medium during cell-culturing production (Figure 1). Meat is a valuable source of bioavailable iron and vitamin B12;2 however, there are challenges with these nutrients being available in cell-cultured meat products. Because iron in meat is primarily present as a highly bioavailable heme form as myoglobin and hemoglobin (Geissler and Singh, 2011), in order for iron to be in the bioavailable form in cell-cultured meat, it will need to be provided in a the cell-culture medium.11 Vitamin B12 is also an essential nutrient for a “complete and balanced” dog and cat food product; however, it is synthesized exclusively by certain species of gut-colonizing bacteria and therefore found solely in food products of that origin.11 For vitamin B12 to be in a cell-cultured meat product, supplementation by biosynthetic microbial fermentation would be necessary. Therefore, nutrients in cultured meat that are not synthesized by muscle cells must be supplied as supplements in the culture medium11 or added to the final product.
Challenges with “designer” meat
Because of the ability to manipulate the composition of the meat, therefore, “designing” meat in an in vitro production system, a favorable nutritional profile can be created for meat in pet food products.2 As mentioned before, this manipulation occurs by adjusting the formulation (e.g., vitamin levels, fat content) of the cell culture medium. However, some authors argue that the process of cell culture is never perfectly controlled and that some unexpected biological mechanisms could occur including epigenetic modifications which could result in some unintended effects on the structure of cell-cultured meat.4 Also, the formulation may be required to change over the course of the culturing process from proliferation period to the differentiation and maturation period, requiring different sets of growth factors.2 If embryonic cells from farm animal species are used as a source of cells, though they have the capability for unlimited proliferation capacity, there may be a slow accumulation of genetic mutations over time.2, 18 Also, adult stem cells are prone to malignant transformation in long-term culture; therefore, to minimize this risk, re-harvesting of adult stem cells may be necessary in an in vitro meat production system.2
Conclusion
Currently, despite the potential for cell-cultured meat to be nutritionally sustainable for pets, there are no cell-cultured pet food products on the market. As technology advances, the idea of cell-cultured meat in pet food becomes more realistic. However, more studies need to be conducted on the nutritional composition of in vitro meat and the technology needed to make it possible. Burdock Group can help companies determine ways to achieve regulatory compliance for ingredients in their pet food products, including cell-cultured meat ingredients, as well as guidance on meeting FDA requirements for having “complete and balanced” in the nutritional adequacy statement for dog and cat food products.
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