Assisted Digestion

Farm animals such as pigs and chickens cannot assimilate all the nutrients they ingest. Their digestive systems do not have all the enzymes required. Nonetheless, researcher Adrian Tsang will provide the missing enzymes from fungi and is adding them to their meals.

By Joël Leblanc


 
 
You can’t fatten pigs on water alone. Québec’s breeders are aware of that: to obtain 100 kg of pork, they have to provide each pig with 300 kg of feed.

In an industry such as agriculture, which has to be competitive, any improvement in this ratio is more than welcome due to the considerable savings it entails.

The feed given to livestock - corn, barley, oats, wheat, soy, canola - cannot be digested 100 percent. “It is mostly starch that is digestible,” says Adrian Tsang, a biology professor at Concordia University and director of the Centre for Structural and Functional Genomics. “The rest, such as cellulose and hemicellulose, passes straight through because these animals lack the enzymes they need to digest them. Overall, pigs, like chickens, can digest about 75 percent of what they eat.” The remaining 25 percent comes out the other end and provides the manure that perfumes the fields of our countryside at spreading time.

 

In simple terms, digestion involves the deconstruction of complex molecules into simpler molecules. To facilitate the reaction, this process usually requires the involvement of a special protein called an enzyme, which remains intact among the final products of the reaction. It is a tool, much like a pair of scissors, which are still scissors after they have cut a sheet of paper.

Enzymes are present in all living organisms. Bacteria, fungi, plants or animals: we all make enzymes. The best-known examples are the enzymes secreted by our own digestive organs (stomach, intestines, pancreas) which break down complex food molecules into smaller pieces that our bodies can assimilate.


“Enzymes are very specific,” Adrian Tsang says.

Each type of enzyme has a structure that permits it to carry out just one specific chemical reaction. In our stomachs, for example, pepsin is the enzyme responsible for degrading proteins into smaller units known as peptides; it has no effect on carbohydrates. Every living organism produces its own specific enzymes.


“Through genetic sequencing, we are exploring the genomes of many species of fungi and are attempting to identify the most promising genes for different cellulases.”

There are as many different types of cellulase as there are types of cellulose. Basically, since enzymes are proteins, and since in order to have a protein, you must first have a gene, each enzyme is encoded by a specific gene in the fungus’s genome.

The fungus Myceliophthora thermophila, for example, whose genome codes for a wide variety of digestive enzymes, produces various enzymes depending on which nutrient substratum it is grown on. Barley, oats, alfalfa, the fungus deploys different enzymes depending on the nature of its meal.

But if livestock don’t have the enzymes to digest cellulose, why not provide them?

This is how Professor Tsang’s basic idea works: add to the animals’ feed the enzymes they need to digest a larger proportion of their diet. Fodder could even be added to feed, which is impossible at the moment given the high proportion of cellulose in straw and hay.

If this were done, cellulose could be broken down into simple sugars that the animals’ bodies could assimilate. Such enzymes already exist in nature.

“Many species of fungi are able to break down cellulose,” Professor Tsang explains. It’s thanks to them that dead trees in forests eventually decompose. If the fungi did not attack wood and make it disintegrate, the forest floor would be covered in dead wood.”

Fungi have evolved to develop enzymatic tools called cellulases whose role is to break down cellulose. 

The enzymes that are added to the feed must be sufficiently numerous and varied to have a wide spectrum and work on all the ingredients in the mixture. In addition, enzymes are temperature sensitive and will have to operate at the internal temperatures of the pigs and chickens.

“The other challenge is acidity,” Professor Tsang adds. “Enzymes are also pH sensitive, so we must select the strains that will work optimally in a variety of conditions encountered along the animals’ digestive tracts.”

Since there are thousands of species and subspecies of fungi, it would take a very long time to test them all one by one to discover which ones fulfill all these conditions. Hence the importance of genomics.

By sequencing the genomes of sixty species and analyzing them in depth, this researcher and his team have created a catalog of all the genes that produce the requisite enzymes. When a new fungus is encountered, there is no need for lengthy laboratory tests to monitor its performance: one look at the genes is enough!

Finally, the work of Adrian Tsang and his team will make it possible to select the best fungus genes to produce specific enzymes. Added to animal feed in powder or liquid form, these enzymes will significantly increase digestive efficiency, resulting in a weight gain in the animals.

For farmers, this means that they will need to give them less feed, and that consequently, there will be less waste to manage. Especially by increasing the proportion of fodder in the feed, the animals will enjoy improved gastrointestinal health and therefore require fewer supplements and less medication. 

All this promises considerable savings, not to mention a reduced need for cereal crops.

 
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