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TUM insect feed mix.jpg Image: P. Straub/TUM
Petri dish with a feed mix optimized specifically for insect breeding.

Nutritional needs of farmed insects studied

While insects have been proposed as a protein source for people and livestock, less is known about dietary needs of insects reared for such uses.

Insects have been proposed as a protein ingredient for people as well as for livestock feed, especially poultry and aquaculture. However, the rearing of insects as food and feed has not received as much attention.

Researchers at the Technical University of Munich (TUM) in Germany and the International Center for Insect Physiology & Ecology (ICIPE) in Nairobi, Kenya, have recently explored what kind of feedstuffs might be suitable for environmentally friendly insect farming.

Given that they generate hardly any greenhouse gases, are undemanding, nutritious and fast growing, insects have generated a lot of hype in recent years, TUM said in an announcement. They are touted as the superfood of the future — cheap suppliers of protein that can even decompose all kinds of residual products.

"This all sounds very promising, but has little to do with reality," said Wilhelm Windisch, professor of animal nutrition at TUM. "Anyone who hopes to keep animals professionally and on a large scale needs to know exactly what kinds of nutrients they need and can consume. And for insects, this is yet to be determined."

In collaboration with a German-Kenyan research team, Windisch has, for the first time, systematically investigated how various feed substrates influence the growth and development of crickets (Gryllus bimaculatus) and locusts (Schistocerca gregaria).

In the wild, both species feed on leaves. "But supplying large insect farms with fresh greens year-round is virtually impossible to implement," Windisch said. "You need feed of verifiable quality and safety that can be dried, stored and transported."

Commercial animal feed would fulfill these criteria, he said, but does it meet the nutritional needs of insects? At ICIPE, the team investigated how the two species responded to different feed choices.

They tested different dry feed variants containing cornstarch, protein and fiber-rich cowpea leaves, protein-rich soy extract and vitamin-enriched carrot powder.

The researchers logged the amount of feed provided every day, weighed the excrements and finally determined the average weight of the adult insects. Two rounds of tests were carried out and evaluated over a three-month period, TUM said.

"The results surprised us," Windisch said. "It was clear to us that the metabolism and digestion are rather different in insects than in conventional farm animals such as cattle, pigs and chickens. What we did not expect were immense species-specific differences."

Locusts, for example, can process plant fibers that are indigestible by humans. Crickets, on the other hand, excrete fiber-rich food. Locusts grow quickly only when fed protein, while crickets need starch, above all, TUM reported.

The source of the differences is still unclear. In their next project, the researchers hope to investigate which enzymes are active in the intestines of various insects and which of them can, for example, convert plant fiber into glucose.

"The research is still in its infancy, but with each result we understand the metabolism and nutrient needs of individual genera better and can use the outcomes in professional insect farms to process biomass that, for example, could not be used previously because it is inedible for humans and livestock can process it poorly, at best," Windisch said.

The research was published in Animal Feed Science & Technology.


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