There are approximately 70 billion land-based farmed animals on the planet, and these animals produce an enormous, incalculable mass of excrement. A recent study has estimated that by 2030 the planet will generate at least five billion tonnes of poo every year, with 80 per cent of it produced by intensive livestock farms. To give a sense of the scale of the phenomenon, it is estimated that animals farmed in the United States alone produce around 40 tonnes of organic waste per second.

"So much manure, so poorly handled, that it leaches into rivers, lakes and oceans, killing wildlife and polluting air, water and land in ways that are devastating to human health," wrote Jonathan Safran Foer in the book Se niente importa. As well as being excessive in quantity, the poo produced by intensive livestock farming has a terrible environmental impact. The excrement of intensively farmed pigs, for example, contains highly polluting substances such as ammonia, methane, hydrogen sulphide, carbon monoxide, cyanide, phosphorus, nitrates and heavy metals. These substances end up in waterways, and the toxic gases evaporate into the air, with serious consequences for human health ranging from asthma to severe neurological damage.

An underestimated problem

The impact of animal waste on our health, as well as reminding us that cheap meat does not exist (intensive livestock farms can perpetuate their business model only because they externalise costs that then fall on the community as a whole), reminds us once again of the absolute necessity of reducing meat consumption. Despite the obvious scale of the problem, treatment facilities for organic waste from farmed animals are almost non-existent. "Animal waste is increasing because, as the global population grows and wealth rises, there is greater demand for animal protein," said Joe Brown, professor of environmental engineering at the Georgia Institute of Technology. "But while many initiatives have been undertaken to safely manage human organic waste, no one seems to be dealing with animal waste."

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The risks for people and the environment

Inhaling the harmful gases emitted by livestock excrement on farms increases the likelihood of developing chronic asthma (particularly in children) and respiratory diseases, can cause mood disorders and, in large quantities, can prove fatal. This faeces, rich in methane and carbon dioxide, also contributes to accelerating climate change. "Agricultural waste is among the main sources of methane emissions across Europe," said Philip Longhurst, professor at the Centre for Climate and the Environment at Cranfield University.

Poisoned water

One of the most visible problems generated by the vast quantities of manure in existence is the pollution of waterways. The high levels of nutrients present in manure, such as phosphorus and nitrates, cause the spread of pathogenic microorganisms that can cause disease in humans and the growth of toxic algal blooms. These can poison wildlife by releasing neurotoxins and can enter the food chain, ultimately being consumed by human beings. In China, for example, where around 28 per cent of the world's meat is consumed, more than half of its lakes are polluted, leading to an increase in diseases such as cholera in many rural communities. "Water pollution is one of the greatest problems arising from the inadequate management of animal waste," explained Oene Oenema, professor at Wageningen University in the Netherlands, which specialises in agricultural studies. "When organic waste is discharged into rivers and then carried into lakes and coastal areas, fish disappear, the water turns dark and black, and there is a high risk of infections being transmitted to humans."

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The most threatened countries

Poo is a global problem with consequences that affect every human being, yet it is particularly severe in certain parts of the world, such as Africa, India and much of South-East Asia, where communities still live in close contact with livestock. While in the West the mechanisation of farming has allowed most people to avoid direct exposure to animal waste, this has not happened in poorer countries, meaning that enteric infections remain a common cause of death, particularly among children. Scientists believe that the majority of these fatal infections are transmitted to humans directly from animals or their faeces, and often, due to the reckless use of antibiotics on farms, these viral strains prove to be antibiotic-resistant.

A new paradigm

To counter this ecological time bomb ready to explode in our hands, it is necessary to develop a systemic approach to the safe management of organic waste from farmed animals. The problem must, however, be addressed at its root: industrial livestock production, which has concentrated animals at absurd densities, is now plainly unsustainable. The livestock industry has pursued the path of cheap animal protein production at the expense of human health and the environment. Consumers can help to reverse this alarming trend, first by understanding the link between animal welfare and public health, and then by using their purchasing power consciously.