That’s roughly 52 billion chickens. In the last 50 years, chicken has moved from being a rare food item, too perishable to mass market, to a staple of protein-rich (and low-fat) diets for a growing human population. But it’s not just the numbers that have altered. In the UK, supermarkets have led the field in changing the ways in which chickens are farmed and processed. Agricultural science and military-style logistics have converted a supplementary source of farm income into a highly organised, vertically-integrated industry.

Chickens are now reared under optimal conditions for economic profit and biological growth. High throughput of densely housed and specifically bred birds increase turnover (or the rate at which fully-grown chickens can be sold for meat). The result is a high-volume, low-margin industry, where the profit on each chicken is small but the real money is to be made in developing market share and volume.

Chickens now reach market at almost twice their previous slaughter weight. More astonishingly, improved housing, the use of enriched feeds and growth-promoting antibiotics mean they reach these new weights in half the time; less than 45 days to grow to market weight (sometimes only 38 days). An average poultry farm now houses several hundred thousand birds, arranged in sheds with 30,000 or so in each, all ‘growing’ in a tightly choreographed system to an established end, when they are ‘harvested’, transported and processed to reach supermarket shelves on time and at the correct price. Industry vets say the birds go through the process like ‘race-horses’.

This is an economic model (pile it high, sell it cheap while tuning biological processes to work as hard as possible at the lathe of production) that some say is symptomatic of our age. The journalist Felicity Lawrence suggests the chicken ‘is one of the defining commodities of our era… the sugar, tea and opium of the age.’ If Henry Ford and his motor cars defined the early 20th century, then the chicken and the often casual labour used to harvest and process its meat, Lawrence has suggested, defines our current times. These times can be characterised by global supply chains, precarious labour conditions, and biological stress.

An average poultry farm now houses several hundred thousand birds, arranged in sheds with 30,000 or so in each (Image: Guitar photographer)

This year is also a year of seemingly unprecedented incidences of bird flu. By the middle of January there had been nearly 650 outbreaks of a deadly and virulent form in Europe, involving more than 200,000 cases. This European strain is currently thought not to be dangerous to people. But in China, another strain was, and has this year reached new levels of infection and mortality. The concern is that this may spread globally. By virtue of its ability to adapt, avian flu is known as a ‘potential pandemic pathogen’.

Standard explanations for the increased incidences of bird flu include failures in something called biosecurity. Disease experts often focus on the site of an outbreak. Those farms that allow poultry to mix with wild birds, or places such as live bird markets (particularly in parts of Asia where there is insufficient hygiene), are often blamed for disease spread. These may well be important points for contagion. Yet, there is another pressing question to ask: are the intensively raised, factory-farmed birds that make up the bulk of the 52 billion killed annually also part of the problem? When you add so many birds to the world’s biomass, all growing at rates and in conditions that change their immune responses, then it seems logical that you have changed the conditions for disease. Perhaps instead of sites, we need to focus on this global disease situation?

The evidence for this shift of attention is starting to emerge. First of all, it is important to say that all farms and forms of production involve plenty of opportunity for microbes, like the avian influenza virus, to circulate. Viruses can move with stock, pests, and with staff. The teams that often move from farm to farm to harvest poultry ‘crops’ may be a particular risk. Second, densely farmed birds may be more infectable. Immune systems are compromised at such growth rates, and once the virus is in a flock, it is clearly going to spread with impunity. Third, there is evidence that this avian biomass is altering the genetic make up of the viruses. In evolutionary terms, if you change a microbe’s environment, you are also going to provide the conditions for changing the microbe. Microbes evolve rapidly, and bird flu viruses are known to be particularly promiscuous, adapting quickly to hosts and so on. The raw material for the flu viruses has increased in number and availability as global production has expanded. The microbes are getting better at taking advantage.

Modernising agriculture is clearly of benefit to a world that needs to eat, and eat safely. And yet, we need to be wary of those tipping points at which the gains of modernisation start to backfire. As I write, the international restaurant chain Chipotle, which uses 64,000 tonnes of chicken meat annually, has announced that it is abandoning fast-growing chickens. Driven by food safety concerns and evidence that slower growth results in less disease, we may be seeing the start of a  crucial shift. The health costs of cheap meat may now be tipping the balance. Redressing that would make this year of the chicken one that could be good for all of us.