Generally, tannins induce a negative response when consumed. Tannins negatively affect an animal's feed intake, feed digestibility, and efficiency of production. These effects vary depending on the content and type of tannin ingested and on the animal's tolerance , which in turn is dependent on characteristics such as type of digestive tract, feeding behavior, body size, and detoxification mechanisms. Intake Tannins may reduce intake by decreasing palatability and by negatively affecting digestion.
Palatability is reduced because tannins are astringent.
Astringency is the sensation caused by the formation of complexes between tannins and salivary glycoproteins. Low palatability depresses feed intake and, thus, animal productivity. Some caution must be taken when interpreting these results. In many trials, commercial tannins sources were used. These types of tannins are usually more effective at lowering feed intakes than naturally-occurring tannins.