Farming insects on manure

More and more companies are farming insects for human consumption and animal feed. A team of scientists led by Prof. Leo Beukeboom researched the suitability of manure as a nutrient medium for breeding insects, which are a high-quality source of protein for humans and animals. The use of chicken and pig manure proved to be a cheap and sustainable way to produce protein and also makes a circular contribution to the manure problem.

What was the project focus?

‘In this project, we aimed to address two challenges at the same time’, says Leo Beukeboom, professor of evolutionary genetics at the University of Groningen. ‘The first is the development of cheaper and more sustainable ways to produce proteins. The second is tackling the manure surplus.’ Insects are a high-quality source of protein for humans and animals, and breeding insect larvae requires much less water and space compared to conventional livestock farming, says Beukeboom. ‘Another advantage is that this approach reduces our dependence on protein sources from abroad’, he says, ‘while making efficient use of the nitrogen in the manure of our livestock and poultry. In other words, we kill several birds with one stone. Moreover, using a waste stream to produce proteins is an ultimate form of circularity.’

In this project, Beukeboom and colleagues from Vrije Universiteit Amsterdam and Wageningen University & Research collaborated with a company to experiment with growing fly larvae on manure. ‘It is in fact mass breeding’, explains Beukeboom, ‘with a production of more than 3,500 kilos of larvae per day. This scale allows us to identify the optimal growing conditions.’

What are the project outcomes?

‘We have shown that it is indeed possible to farm insects on manure’, says Beukeboom, ‘and that production can be further optimised by varying different breeding factors. Both chicken and pig manure are suitable. We mainly experimented with chicken manure, but there are indications that pig manure may be even better.’

Wageningen colleagues investigated the nutritional value of manure for larvae. ‘They discovered that the larvae grow better if you enrich the manure with around 15 percent starch’, says Beukeboom. Temperature was also an important factor. ‘We experimented with different temperatures, and 32 degrees turned out to be optimal.’ Amsterdam colleagues discovered that you can improve the flies’ genetics through selective breeding, for instance to produce flies that grow better on extra sugar or fat. ‘This allows you to develop breeding lines that perform better on certain substrates’, explains Beukeboom. ‘In Groningen we experimented with ways to breed more females, relative to males. This provides an economic advantage, because only females lay eggs. This was also successful. All of this shows that there is still a world to discover – and that production can be optimised even further.’

Chickens love fly larvae, notes Beukeboom. However, European legislation has long prohibited the use of animal protein in feed, in response to mad cow disease. Insects have recently been made an exception – unless they are grown on manure. ‘If you want the legislation to change, you first have to have more information on safety and benefits’, says Beukeboom. ‘Our research makes an important contribution in this regard. It shows that manure is useful, and that production can be increased through adjustments to the manure and the breeding conditions, and through selective breeding of the housefly.’

Text: Nienke Beintema

This article was published in the magazine Closed Cycles, a result of the research programme: New Insights into the Transition to a Circulair Economy by the Dutch Research Council (NWO). Read more about the other research projects.