Blog essay authored by Catherine Oliver (Postdoctoral Research Associate, ERC Urban Ecologies project, Department of Geography, University of Cambridge) and Jonathon Turnbull (PhD Scholar, Department of Geography, University of Cambridge). Both are invited contributors with the Rescaling the Metabolic: Food, Technology, Ecology Research Network at CRASSH.

Eggs collected from hens at an industrial farm. Image by Jo-Anne McArthur/We Animals, 2019. 


The industrialisation of chicken farming has divided chickens into ‘broilers’ for meat and ‘layers’ for egg production (Davis, 2009). Both the broiler and the layer are the result of at least a century of fowl-breeding. Driven increasingly by market logics, farmers have contended with raising profitable birds, which involved selective breeding and genetic manipulation to increase their productivity whilst driving down costs, notably of feed. The coalescing of these demands has led to at least a century of multi-scalar manipulations. At the genetic scale, selective breeding aims for genetic ‘robustness’ (Mckay et al 2018). At the environmental scale, light exposure and access to space are manipulated to meet the productivity demands of capitalist temporalities (Davis 2009). And, at the metabolic scale, nutritional management experimentation pursues efficient growth rates.

Traditionally, egg production dominated chicken agriculture in the United States but by the end of the 20th Century, it was eclipsed by broiler business (Bell and Weaver 2002). Egg consumption dropped in the latter half of the twentieth century due to salmonella fears, but as a proportion of meat eaten by Americans, chicken rose from 23% to 43% (Davis 2009). Broiler chickens have become paradigmatic metabolic labourers (Beldo 2017); compared to 50 years ago, they grow twice as large in half the time (Barua, White and Nally 2020). Broiler meat has become emblematic of the geographical nature of metabolism, whereby ‘capitalist relations move through, not upon, space’ (Moore 2017, 313) with intense material consequences. However, in this essay, we attend to other experiments involving the metabolic processes of chickens, their eggs and more-than-human health to highlight how metabolism is a concept that stretches across geographical scales and sites.

Metabolic experiments with chickens are aligned with global shifts in human nutrition and diets. The selective breeding of chickens for food dates to at least the sixteenth century (Wood-Gush 1959) but it was the nineteenth century that ushered in a new attitude towards meat consumption in Britain that had ripples the world over. Meat ‘was regarded as a vital source of British power and stamina, a weapon of war and a tool of conquest’ (Otter 2020, 21). Chicken consumption has risen since the nineteenth century, today being the most popular meat in the Western world, and second only to pork consumption globally. While pork and beef consumption has remained steady since 1990, chicken consumption has increased by 70% in OECD countries (The Economist 2019). The ‘meatification’ of the planet has led to ‘selection for specific traits’ and ‘the elimination of undesirable ones’ in farmed animals, which has led to significant reductions in effective population size and overall genetic diversity of chickens (Otter 2020, 32). The composition of chicken products, both flesh and eggs, were subject to metabolic experimentation in animal sciences developing simultaneously with human nutritional science. Thus, contemporary chickens and eggs are the bearers of genetic and nutritional knowledge which, through molecular governance, stitch together human and animal metabolic interdependencies.

Metabolising chickens

In Making Meat, Boyd traces ‘efforts to understand and improve the diets of chickens as a key component to accelerate growth rates and increase metabolic efficiency’ (Boyd 2001, 644). The alignment of agricultural chemistry and nutritional science meant chickens were regularly used in studies on essential nutrients, particularly vitamins. This expansion of knowledge regarding chicken nutrition meant that ‘by World War II, the nutrient requirements of chickens were known more precisely than any other commercial animal species’ (Boyd 2001, 645). These experiments were not merely on chickens, though. Rather, they were with chickens, albeit by force. The logics of capital pervaded the development of understandings of chickens’ nutritional requirements. This required chicken bodies to undertake forms of ‘nonhuman labour’ (Barua 2017) as ‘workers in the shadows of capitalism’ (Barua 2018). Chickens, therefore, undertake distinct labour ‘occurring at macrobiotechnological and microbiotechnological levels’ (Beldo 2017, 118). This labour is congealed in metabolic experiments.

One such experiment involves light used to disrupt chicken metabolisms to elongate their productive hours. Sunlight, or UV light simulators, stimulates the pituitary gland, signalling to the ovaries to increase the production of follicle-stimulating hormones (Smith and Daniel 1975). In industrial egg farms, the lights are kept on for 16 hours mimicking long summer days to foster daily laying. Light is also used to force moulting, where chickens are exposed to 24 hours of continuous artificial light, followed by being deprived of food for 14 days with exposure to 10 hours of light per day (Davis 2009). Inducing an intense and compressed moulting process lasting one or two months – which would ‘naturally’ occur over the course of a year – forces the chickens into their next laying cycle. Forced moulting prevents the ‘wasteful’ redirection of energy from laying to growing feathers. These hens are alienated from their own metabolic labour and their ‘natural’ metabolic clocks, whilst also having their spatialities tightly restricted and controlled.

In the twentieth century, chickens were also implicated in the metabolization of waste. Dairy waste was introduced to chicken diets, making their manure high in casein protein (Landecker, 2019). This chicken manure possessed ‘valuable fertilizing properties,’ but efforts to convert it into a dry substrate for sale and circulation were largely unsuccessful (ibid., 535). In 1927, a patent for the chemical treatment of this manure noted that the drying process could be facilitated by ‘the addition of poultry feathers or whole bird corpses’ (ibid, 536). As part of this fertilizer, chicken bodies were fed to crops and metabolised by plants. A ‘chemical gaze’ (Landecker 2019) had fallen upon chicken metabolisms; all aspects of chicken life – bodies, waste, produce – were seen in terms of their chemical constituents and capacities for chemical transformations.

Researchers at the University of Wisconsin in the early 1920s ‘discovered that vitamin D, when added to a chicken’s diet, prevented leg weakness’ (Boyd 2001, 638), leading to the widespread addition of cod-liver oil to chicken feed. Vitamin D-supplemented chickens could be kept indoors all year round, reducing their spatial requirements, reducing the zoonotic risks of contact with ‘wild’ birds, and setting the stage for another century of experimentation in confinement and metabolic intensification.

Floor-raised egg-laying hens. Image by Jo-Anne McArthur/We Animals, 2019

The chicken and the egg

Attempts to fragment and automate the chicken draw on biologic and metabolic knowledges of nutrition, digestion, and reproduction. Chickens’ vitality overflows conceptions of metabolism as a ‘solely biomechanical process’ (Beldo 2017, 112), yet this same capacity of life makes them ideal experimental subjects. In this vision of the chicken, feed goes in and eggs come out. Metabolic labour is conceived as an intermediary process, which Haldane (1931, in Landecker 2013, 515) describes as ‘the transformations undergone by matter in passing through organisms.’ This refining of the industrial metabolism is undertaken in ‘the exact determination of which enzymes and which vitamin cofactors were necessary to catalyze what reactions within the framework of the cell’ (Landecker 2013, 496).

Eggs offer a ‘nutritionally complete and well balanced’ source of nutrition and are labelled ‘a nearly complete food’ by Smith and Daniel (1975, 193). The nutritional composition of eggs varies; fat-soluble vitamins A, D and E, and water-soluble vitamin B12 are all influenced by levels of fat and drugs in chicken diets (Naber 1979). As highly digestible foods, eggs and their proteins possess ‘biological activities of interest for human health’ including ‘antimicrobial, antioxidant, and anti-cancerous properties’ (Sophie Réhault-Godbert et al 2019), the composition of which can be altered even in colour, with changes in carotenoids determining the shade of egg yolk (Bouvarel et al 2011). The human-altered egg is thus a far from ‘natural’ food.

In contemporary metabolic theory, chemical conversions of food into energy have been replaced by understandings of ‘food [as] a conditioning environment that shapes the activity of the genome and the physiology of the body’ (Landecker 2011, 167). Modern malnutrition does not only arise due to nutritional deficiency, but also via excess (McMichael 2005). The ‘challenge for nutrition science is to develop new understanding and strategies to enable a balance between promoting, equitably, the health of humans while sustaining the long-term health of the biosphere’ (ibid., 706). In these nutritional excesses and deficiencies, metabolic experiments attempt to make the egg a conduit for nutritional tweaking.

Omega-3 (n−3 PUFA) is a polyunsaturated fatty acid found in flaxseed, fish and algae: an ‘ancient, human biology-attuned nutrient’ (McMichael 2005, 710) which is involved in the development and maintenance of the brain, and is helpful in preventing cardiovascular pathologies, and potentially stress, depression and dementia (Bourre 2005). The recommended intake of this fatty acid is rarely met in Western diets, leading to experiments to modify eggs’ Omega-3 profile through feed supplementation (Fraeye et al 2012). The use of dietary supplements for egg-laying chickens occurs for two reasons. First, so that living animals can efficiently distribute the desirable nutrients throughout their tissues (Bou et al 2009) – a process that technology cannot yet match. And second, because dietary supplementation is safer than transgenic modification or adding bioactive compounds to the final product. Via the metabolic labour of chickens, the egg is a conduit, produced and tailored for human nutritional needs and desires.

Post-productive metabolism

Changing patterns of human consumption are reconfiguring the Earth’s geology and biosphere. The broiler chicken has been proposed as a distinct new morphospecies signal (Bennett et al. 2018); a characteristic of the Anthropocene era. With a population of over 22 billion, the rate at which chicken carcasses are accumulating is unprecedented in the natural world (Bennett et al. 2018). Even as growth rates slow down, global egg production has increased from 20 million tonnes to over 70 million tonnes per year since 1961.

This waste problem associated with chicken carcasses has inspired efforts to develop methods for utilising spent, post-productive, hens. ‘Ground spent hen’ is used in hen meal that is fed back to chickens. It is also used in cheap human baby food, reconstituted chicken products like chicken nuggets, and in commercial pet food products (Alexander et al 2020). New utilisations of chickens’ post-productive bodies are continually emerging, notably as ‘a sustainable biomass source to produce fuels’ (Safder et al, 2019). The use of spent hens as such retains post-productive chickens’ bodies in the flows of industrial metabolism, connecting chickens back into the wider nutritional environment and demonstrating how metabolic intensification goes hand-in-hand with the capitalist logics of efficiency.

Expansive experimentations with chicken nutrition during the history of industrialisation have been the basis for more-than-human metabolic knowledge. Attending to chickens opens questions of what and who is inside and outside of the metabolic process. If the egg is used as a conduit for refining human nutritional intake, the chicken body becomes a space (and process) through which desirable nutrients are delivered into human food. Chickens are alienated from their own bodies, even as egg production relies on their currently irreplaceable metabolic labour. Chickens are always implicated in networks of capital, wherein value is eked out of bodies, both living and dead (see Gillespie, 2014). The metabolic regulation of chicken lives operates on multiple registers – across species, bodies, and cellular and genomic processes – but also across geographical scales, where chickens and their farming are produced and have effects internationally.

Chickens first became the subjects of an international project in the eighteenth and early nineteenth centuries; the time when genetic and breeding sciences were developing. These developments also coincided with ‘the importation into the West of the giant Asiatic breeds’ (Smith and Daniel 1975, 205). With the advent of poultry shows in the USA and Britain, ‘so began the odyssey of the modern chicken propelled out of the obscurity of the barnyard onto the national and international scene, traded in and speculated on like a growth stock’ (ibid, 208). Both exotic variations and more familiar farmed hens were imbued in a particular politics of production wherein the ‘ideal chicken’ was pursued. This involved breeding for traits such as faster laying, whilst attempting to lessen traits that would impede production, such as broodiness. This ultimately led to the proliferation of the Leghorn, ‘a reliable layer’ with ‘the least tendency to broodiness’ (ibid 237-9).

Unsurprisingly, the industrialisation of chickens is not without negative consequences, notably in terms of significant reductions in their genetic diversity (Granevitze et al 2007), reducing genetic resistance to infectious disease (Zekarias et al 2002). Where ‘scientists see bird populations as a reservoir for human pathogens’ (Keck and Lakoff 2013), disease outbreaks in avian populations might serve as ‘sentinels’ (Keck 2013). Industrial chicken farming continues to produce interspecies ‘virulent zones’ that are neither temporally nor geographically bounded. As Wallace contends in relation to the highly pathogenic avian H5N1 infection: ‘the origins… are multifactorial, with many countries and industries and environmental sources at fault’ (2016, 79), not least the United States’ industrialised model of vertically integrated farming. The manipulation of chicken metabolisms has reverberating and unpredictable consequences across space, time, and species.

In this essay, we have attended to how chicken metabolisms are manipulated at a range of scales in pursuit of profit and human nutrition. From strictly controlling their environmental conditions to the recycling of spent hens into wider nutritional environments, chicken metabolisms are implicated across scales. Following Landecker (2011), the chicken is conceptualised as a ‘singular inward laboratory’ where the metabolism forms a process to be controlled, monitored, and manipulated. As such, chickens’ metabolic labour has been intensively fine-tuned to become a conduit for, and synthesiser of, nutritional value for humans. Such understandings allow chickens not only to be alienated from their metabolic labour as with all farmed animals, but also to be uniquely constructed as conduits that transform and improve matter as it passes through them.



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