The legendary abilities of goats and sheep to digest a wide range of inedible materials could help scientists produce cheaper biofuels.
Researchers say fungi from the stomachs of these animals produce flexible enzymes that can break down a wide variety of plant materials.
The scientists say that in tests, the fungi performed as well as the best engineered attempts from industry.
The study has been published in the journal, Science.
Fuel from food
Environmentalists have long criticised the current generation of biofuels that are produced from crops, such as maize, as they believe that using land for fuel instead of food drives up prices and impacts the poor.
Researchers have had some success making usable fuel from food and animal waste. But, so far, the ability to efficiently use the vast majority of cheap, waste organic material has eluded them.
The problem with turning wood chips and grasses into fuel is the matrix of complex molecules found in the cell walls of these tough materials.
Industrial attempts to break these down into the type of sugars that can be refined for fuel often require preheating or treatment with chemicals, which add to the complexity and the cost.
To solve the problem, researchers have turned to the well-known abilities of goats and sheep to digest almost anything they eat.
Researchers believe this facility is the result of the presence of anaerobic gut fungi, organisms that have existed since the time of the dinosaurs.
To test their ideas, the scientists collected fresh manure from a zoo and a stable and isolated three previously uncharacterised cultures from goats, sheep and horses.
They found that these fungi excrete enzymes that break down a wide range of plant material.
Unlike the best genetically engineered enzymes produced by the biofuel industry to date, they discovered that the sheep and goat fungi produced many hundred more of these proteins.
These were "substantially better" at breaking down a type of material found in wood - and when the researchers changed the diet of the fungi from grass to sugar, they found that the organisms changed the type of enzymes they produced in response.
"Because gut fungi have more tools to convert biomass to fuel, they could work faster and on a larger variety of plant material," said Prof Michelle O'Malley, the lead author from the University of California, Santa Barbara.
"That would open up many opportunities for the biofuel industry," she said.
The scientists involved say that these types of fungi can be found in a wide variety of animals apart from sheep, ranging from cattle to elephants.
"In our work we have identified hundreds of enzymes from anaerobic fungi with commercial biotechnology potential," said Prof Michael Theodorou from Harper Adams University, UK, another author on the paper.
"We need to invest more resources to study this group of relatively unknown micro-organisms. They may hold the key to the renewable technology of effective biomass conversion. Their full potential must be explored and exploited."