If we can’t dramatically cut meat consumption then intensive ‘factory farming’ may be comparatively less risky, say authors

The industrial farming of animals such as pigs, poultry and cattle to provide meat for hundreds of millions of people may reduce the risk of pandemics and the emergence of dangerous diseases including Sars, BSE, bird flu and Covid-19 compared with less-intensive farming, a major study by vets and ecologists has found.

Despite reports from the UN and other bodies in the wake of Covid linking the intensive farming of livestock to the spread of zoonotic (animal-borne) diseases, the authors argue that “non-intensive” or “low-yield” farms pose a more serious risk to human health because they require far more land to produce the same amount of food.

This, it is argued, increases the chances of “spillover” of dangerous viruses between animals and humans because it drives habitat loss, which displaces disease-carrying wild animals such as bats and rodents and brings them into closer contact with farmed animals and humans. The authors of the report, published in the journal Royal Society Open Science, acknowledge that the rapidly increasing consumer demand for meat and other animal products is posing a significant risk to humanity. “The risks of emerging infectious diseases are escalating. Livestock biomass now vastly exceeds that of wild mammals and birds, and livestock hosts increasingly outnumber wildlife hosts for pathogens they share”, it says.

While eliminating the farming of animals would take away a lot of the disease risk, say the authors, they argue that a dramatic reduction in meat consumption would be “challenging” to achieve. So instead the report looked at whether intensive or less intensive farming was a better option for reducing disease risk.

Intensive livestock farming has been widely blamed for increasing the risk of bird and pig flu and other pandemics because of long-distance livestock movements, crowded farms, poor animal health and welfare, low resistance to disease among animals and low genetic diversity.

But data on the emergence of disease in intensive farms is limited, says the report, and typically ignores how land use affects risks.

“High-yield or ‘intensive’ livestock farming is blamed for pandemics, but those calling for a move away from intensive farming often fail to consider the counterfactual – the pandemic risk of farming less intensively and particularly the consequences for land use,” says the lead author, Harriet Bartlett.

“Low-yield farms need far more land to produce the same amount of food compared with high-yield farms. A widespread switch to low-yield farming would result in the destruction and disturbance of vast areas of natural habitats. This increases the risk of viral spillover [ie the first transmission from a wild animal] by disturbing wildlife that may well host the next pandemic virus and increasing contact between wildlife, people and livestock.

“Lower-yielding farms typically involve larger livestock populations, poorer biosecurity, more workers and more area under farming, resulting in different, but not necessarily lower, disease risks than higher-yielding systems producing the same amount of food”, says the report by vets and ecologists at Cambridge and Leeds universities.

A global shift away from intensive farming would require an area of land almost as large as India, inevitably increasing the risk of spillovers, Bartlett says. “The conversion and fragmentation of natural habitats means that we are farming in places where livestock and people [come into closer contact] with stressed populations of wild animals.”

Evidence that zoonotic diseases emerge more often in intensive-farming systems rather than extensive ones is hotly debated, with governments and the £150bn-a-year poultry and livestock industries arguing that intensive farming is generally extremely safe and now essential. Animal welfare campaigners argue that such farms are hotbeds of disease.

The report says poultry farms described as both “industrial” and “back yard” played a role in the 2004 outbreak of highly pathogenic avian influenza (HPAI) in Thailand. However, which one played a greater role – “spillover in ‘back-yard’ production due to poor biosecurity permitting contact between wild and domesticated birds, or amplification and reassortment from low to high pathogenicity in ‘industrial’ systems” – remains open to debate.

The intensive farming of pigs close to bat colonies is widely thought to have led to the emergence of the Nipah virus in pigs and humans in 1999, and of Mers in Saudi Arabian camels. World Health Organization investigators have stated that Covid is likely to have originated in a Chinese wildlife farm before being spread in an urban “wet” market. Dr Guillaume Fournié, an epidemiologist at the Royal Veterinary College in London, said supposedly better biosecurity on intensive farms was not always a defence against the spread of disease.

The recent wave of bird flu outbreaks in Europe had “shown how difficult it can be to ensure optimal biosecurity standards and how this may lead to onward spread in high farm-density areas”, he said. Sign up for the Animals Farmed monthly update to get a roundup of the biggest farming and food stories across the world and keep up with our investigations. You can send us your stories and thoughts at animalsfarmed@theguardian.com