As a mostly-vegetarian scientist and smallholding farmer, it was my new challenge to consider the role of animals in an ecological farming system aimed at both protecting nature and feeding the world equitably.

Inspired by the fascinating analysis of the livestock system by author Simon Fairlie, I took a hands-on approach and decided to raise two piglets on a default diet! This meant sticking to an important condition: using only 'feed' not required or not competing with human food. For us, as for Simon Fairlie and his so-called 'default' livestock system, the choice of feed is at the core of any ecological livestock system.

Organic Farming Route through Friesland

Ecological livestock integrates farm animals as essential elements in the agriculture system; they help optimise the use and cycling of nutrients and, in many regions, provide necessary farm draught power.

Ecological livestock relies on grasslands, pasture and residues for feed, minimising use of arable land and competition with land for direct human food production and protecting natural ecosystems within a globally equitable food system.

In a new report, called Ecological Livestock, which Greenpeace International published today, we identify some of the options for reducing livestock production and consumption to fit within ecological limits, with a focus on Europe.

Back to my smallholding and pig-rearing, this meant finding ways to feed the piglets with 'residues' that were not needed for feeding people. As I found out, pigs eat a lot (and grow quickly) and they like to eat almost everything.

Stale bread from a nearby school canteen, any vegetable peelings we could get hold of or a huge amount of crop residues. All seemed delicious to our piglets. Neighbours were surprised: aren’t you feeding maize and soy to the pigs? Not buying feed?

Intensive animal production needs huge amounts of feed. Feed that competes with land needed to grow food for direct human consumption and which often grows in croplands that were once forests that held the biodiversity and the sequestered-carbon we need to survive.

And, as I quickly found out, those pigs were eating too much! As recent science tells us, "an astonishing 75% of the world’s agriculture land" is devoted to raising animals, including both the land used to grow crops for animal feed and pasture and grazing lands.

Dairy Farming in UK

Like anyone living or passing near an intensive pig farm quickly notices, the problem with industrial livestock is also at the other end. Industrial livestock produces immense amounts of manure that end up polluting soils, water systems and the atmosphere.

At the same time, manure is a rich source of organic matter and nutrients needed for soil fertility. However, as industrial livestock operations are often thousands of kilometres away from where the manure would be needed to grow feed crops, manure ends up being wasted.

The manure from our two pigs, after being safely composted, will be used to fertilise our farm, thus avoiding two problems: polluting other land and having to rely on chemical fertilisers (that are also polluting). That is what ecological soil fertility is about: reusing all residues to make soils fertile and avoiding the negative consequences of agrochemical dependency.

The new Greenpeace report outlines options for limiting the massive impact of livestock on our planet. Globally, science shows us clearly that we are currently over-producing and over-consuming animal proteins, particularly in rich societies.

As the pigs showed me, even my extended family of about hundred people was unable to provide sufficient food residues to raise two animals a year (and food waste should always be kept to a minimum, even if we are feeding animals with it.)

In the end, I had to buy some maize feed to keep up with their appetite. Maybe it’s time to limit our appetites for animals too. A plant-based diet is better for our health, for our climate, for our forests, for our rivers and oceans, and for global food security, and it also helps keep food prices low. As author Michael Pollan smartly put it: Eat food. Not too much. Mostly plants.

Reyes Tirado, Senior Scientist at Greenpeace International

Iza Kruszewska and Reyes Tirado coordinated the production of this new report on Ecological Livestock published by the Agriculture campaign within Greenpeace International