Feeding livestock leftovers = more sustainable livestock systems

June 4th, 2018

The problem: Livestock can negatively impact the environment

Livestock are a valuable food source but can cause environmental degradation. The growth of livestock production in the recent decades has been a key driver of the conversion of forests and grasslands into agricultural land, resulting in greenhouse gas emissions and loss of biodiversity. Livestock currently dominate human-generated greenhouse gas emissions from the food system, being responsible for about 60%.

Thus the role of livestock in the food system is heavily debated. From this debate arises the question: what role could livestock play in an environmentally sustainable food system?

The solution: Feeding livestock leftovers

In a study by Van Zanten et al. 2018, recently published in Global Change Biology, we demonstrate that the ‘default livestock’ concept (see above figure), could provide a significant amount of our daily protein needs, while minimising negative impacts on the environment. Under this concept, livestock would be mainly fed on leftover food and grass resources rather than human-edible biomass, such as grains.

“We found that 9-23 g per capita of animal protein per day could be produced in this way, which is significant considering that a human needs about 50 g protein per capita per day. This is 20-40% of the human protein needs” said co-author Dr Mario Herrero.

“By feeding livestock wasted food or leftover grass resources, nutrients are recycled back into the food system that otherwise would have been lost in food production” said Dr Mario Herrero.

But just how much protein could ‘default livestock’ produce?

The study estimated the current daily consumption of protein per capita in different regions against the range of animal-source food that could be produced through ‘default livestock’ (see below figure).

It identified that overconsumption, relative to the planet’s land boundary, is evident in most developed regions. However, in Asia and Africa, where many people’s nutritional needs are not met, the consumption of animal-source food is still within the land-use boundary. This means that people in these regions could, in the short term, maintain or increase their consumption of livestock, allowing them to better meet their nutritional needs.

Figure: Current protein supply per person per region compared with the minimum global average default livestock value of 9 g protein per person per day, and the maximum default livestock value based on of 23g protein per person per day. Figure from Van Zanten et al. 2018.


We need to find better ways of managing our food systems to enable us to minimise negative environmental impacts while meeting human nutrition needs. Thus, managing the animal-source consumption, now and in the future, is an essential component of achieving sustainable nutrition security.