Tannin

Tannin toxicity in ruminant animals 

Tannins are phenolic compounds that are commonly found in plants. These compounds play a role in protection from predation, as well as growth regulation, when they are digested by herbivores. 

Found in the leaf, bud, seed, root, and stem tissues, tannins are widely distributed in many different species of plants. 

Tannins are separated into two classes: 

1. hydrolysable tannins and 

2. condensed tannins. 

Depending on their concentration and nature either class can have adverse or beneficial effects. When ruminants digest some plants, they acquire a surplus of tannins and rumen microbes do not have the enzymatic ability for degrading condensed tannins. 

In fact, digestion of tannins by ruminants in large amounts can reduce the activity and the proliferation of ruminal microorganisms reducing ruminal biohydrogenation.

Tannins can also precipitate proteins and inhibit the absorption of nutrients. Very high levels of tannin intake can produce toxicity that can even cause death. Animals normally consuming tannin-rich plants can develop defensive mechanisms against tannins, such as the strategic deployment of lipids and extracellular polysaccharides that have a high affinity to binding to tannins. 

These mechanisms prevent tannins from causing adverse effects on rumen microbes.