Does intensive livestock farming increase the risk of pandemics?

It has been suggested that intensive livestock farming may increase the risk of pandemics of zoonotic origin because of long-distance livestock movements, high livestock densities, poor animal health and welfare, low disease resistance and low genetic diversity. However, data on many of these factors are limited.

In a paper in Royal Society Open Science, a team of scientists led by the University of Cambridge found a lack of sufficient evidence to conclude whether intensive or extensive farming is least risky, and say there is evidence that the move away from intensive farming might actually increase the risk of pandemics. They call for more research to be done before changing policies or incentivising a particular type of farming.

“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,” said lead author Harriet Bartlett, a PhD candidate at Cambridge’s Department of Zoology.

“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 by disturbing wildlife that may well host the next pandemic virus and increasing contact between wildlife, people and livestock,” Bartlett said.

The researchers note that rapidly increasing global demand for animal products means that livestock population is now higher than ever and still growing. Most animal products now come from intensive farms, but such farms are thought be risky due to their crowded conditions which increase the chance of diseases ‘taking off’ and spreading rapidly.

However, intensive farms need less land than extensive, or ‘free range’, farms to produce the same amount of food – both to grow their feed and to rear their animals.

Growing demand for livestock products has caused dramatic habitat loss, say the researchers, which means we are now farming in places where livestock and people are coming into frequent contact with wildlife. They say that this contact with increasingly disturbed, stressed, and infected wildlife makes the spillover of zoonotic viruses into people or livestock more likely.

“If we were to switch from the current system to one based on extensive farming, we would need substantially more land to meet demand – resulting in the conversion of habitat roughly the size of Brazil and India between 2009 and 2050,” said paper co-author Prof Andrew Balmford. “This could increase the contact between people, livestock and stressed wildlife – including wildlife that might well host the next pandemic virus.”

“Intensive farms may have a greater risk of takeoff, but extensive farms may have greater risk of spillover,” he said.

The researchers say that we do not know which risk is more important for preventing future pandemics, and so it is currently impossible to determine which types of farms carry least risk overall.

Article: Bartlett, H., Holmes, M. A., Petrovan, S. O., Williams, D. R., Wood, J., Balmford, A. (2022). Understanding the relative risks of zoonosis emergence under contrasting approaches to meeting livestock product demand. Royal Society Open Science, 9(6), 211573, doi: 10.1098/rsos.211573

[SOURCE: University of Cambridge]