Superbug risk from tonnes of antibiotics fed to animals
25 March 2015 by Debora MacKenzie
IT HAS been called an apocalyptic threat, and our hunger for meat will only make it worse. The world’s farmers are feeding an estimated 63,000 tonnes of antibiotics to chickens, pigs and cattle every year, encouraging the evolution of resistant bacteria, which have repeatedly been linked to human infections.
The team behind the estimate – the first of its kind – also forecasts that antibiotic use will climb by 67 per cent to 106,000 tonnes by 2030. Most of the increase is expected to be in middle-income countries, but once resistant bacteria appear, they can spread around the world.
The problem is worsening as people prosper and can afford to eat more meat and dairy. Such is the demand that, according to team member Tim Robinson of the International Livestock Research Institute in Nairobi, Kenya, the total biomass of the world’s livestock now outstrips that of people.
Traditionally, livestock have foraged for grass or scraps in pastures or alleys between houses. But producers worldwide are increasingly switching to intensive production with animals fed in crowded barns, as already happens in rich countries. Even if the animals are not sick, the feed routinely contains low doses of antibiotics to make them gain more weight per unit of food eaten, boosting slender profits.
Livestock accounts for some 80 per cent of the antibiotics consumed in the US, but there are no corresponding figures for global consumption. To fill this gap, Robinson’s team looked at the amount of antibiotics farmers in rich countries feed to intensively reared livestock. Then they mapped pig, chicken and cattle populations worldwide, noting the proportions that are raised intensively, and how those are predicted to grow over the next decades.
With these details, the team’s computer model could calculate the antibiotics consumed by livestock in every country.
China is the worst offender: its livestock get through 15,000 tonnes a year, 50 per cent more than the US, the next on the list. Surprisingly, Germany comes fourth despite a 2006 European Union ban on antibiotic growth promoters.
China’s consumption is set to double by 2030, along with that of India, Brazil and South Africa. In countries such as Indonesia, Nigeria and Peru, it will more than double (PNAS, doi.org/242). And these estimates are likely to be conservative, says Robinson, due to simplifications in the model.
Frank Aarestrup of the Technical University of Denmark in Lyngby, who raised the alarm about antibiotics in livestock in the 1990s, welcomes the figures even if they are an underestimate: “It gives us something to argue from.” He adds that the question now is whether these countries will follow the US example or Denmark’s, which has eliminated the use of antibiotic growth promoters. “That’s going to be a challenge,” says Robinson.
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