Tannins and Phenols

What are tannins and phenols?

Tannins are chemicals which bind to protein and make it unable to be absorbed by animals. Tannins are generally found in greater concentrations in shrubs and trees, and can severely limit how much protein an animal is able to take in.

Phenols are toxins produced by plants, and serve to deter herbivores from eating their tissues.

How are tannins and phenols measured?

Tannins are water soluble, and by heating and sonicating (think of your sonic toothbrush) the forage sample in a water solution we can extract the tannins from the dried sample into the water solution. From there, Rachel (our awesome lab tech!) works some magic where she puts proteins (“bovine serum albumin” – blood proteins from cattle) in with the extracted tannin solution and measures how much of the tannin/protein binding occurs. From the extent of the tannin/protein binding, we can figure out the level of tannins in a forage sample.

Phenols are measured in a similar way – phenols are extracted from a forage sample into a water solution, and then we add a set of chemicals which directly react with any phenols in the solution. The higher the phenol concentration, the more blue the solution appears. We can directly measure the “blue-ness” of a sample using a fancy machine called a spectrometer, which measures how much light of a particular wavelength is absorbed by a solution when passed through it.

Why is it important to measure tannins and phenols?

Tannins and phenols are examples of antinutrients – things which are generally harmful to an animal. Tannins directly reduce the protein content of a sample (by making it unavailable for digestion), while phenols require energy and materials from the animal in order to excrete them after they are ingested (think of your liver after a heavy night of drinking). It’s important to know these in order to figure out the overall quality of a forage sample for an animal.