Dietary inclusion of tannins to replace antibiotics in ruminants

Chemical structure and presence of tannins

Tannins are a heterogeneous group of phenolic compounds with diverse structures that share their abilities to bind and precipitate proteins.

They are usually classified into 3 main groups:

• Hydrolyzable tannins (HT)
• Condensed tannins (CT) (also called proanthocyanidins)
• Phlorotannins (PT)

The first 2 groups are found in terrestrial plants while PTs are found only in marine brown algae.

Tannins are widely distributed amongst the plant kingdom, being especially abundant in nutritionally important forages, shrubs, cereals and medicinal herbs (Salunkhe et al., 1982, Wang et al., 1999).

Tannins tend to be more abundant in the vulnerable parts of plants, e.g., new leaves and flowers (Terrill et al., 1992, Van Soest,  1982,  Frutos et al. , 2004).

Chemical structures and tannin concentrations vary greatly between plant species, growth stages and growth conditions.

Biological activity of tannins

Tannins serve as part of the plant’s defense system against pathogen invasion and insect attacks. Thest possess numerous biological activities, such as:

• Antimicrobial properties
• Antiparasitic properties
• Antioxidant capacity
• Antiviral properties

These activities vary greatly depending on the chemical composition and structure of tannins. As well as due to other factors like: microorganism species, growth stages and/or host species (Hoste et al., 2006, Hoste et al. , 2012).

Use of tannins in ruminants