Abstract:
Chemically distinct, hydrolysable and more stable condensed type of tannins have been identified in
forages. The values depend on the analytical method used. Factors affecting tannin content of foliage were:
climatic factors (higher in tropical species and under drier conditions), soil fertility, species (shrubs and tree
species having higher levels than pasture types), stage of growth (less mature having higher levels) and plant
part of significance was the accessibility to browsing and the act itself resulting in higher tannin levels,
recognized as a defense mechanism mediated from affected plants to others through ethylene produced due
to browsing to increase tannin levels in uuafTected plants to discourage browsing. Younger parts and those
accessible for browsing having Higher levels are other defense mechanisms. Proline in saliva of deer binds
with tannin in shrubs and tree species offering a counter mechanism by browsers while the saliva of grazers
(cattle and sheep) is proline-free. Depending on the level of tannins in a diet, the effect may vary from
beneficial (2-4%) through antinutritional (5-9%) to toxic and lethal (>9%). Effects are mainly due to
complexing with enzymes/protein thereby reducing rumen NH3, microbial activity, nitrogen and dietary
dry matter utilization, resulting in decreased intake and animal performance. Polyethylene glycol (PEG) in
feed preferentially binding condensed tannins improved the utilization of protein more than that of the dry
matter with the effect being greater at higher tannin levels. Split compared to single dose PEG seemed more
effective. Limited evidence indicated that PEG promotes selection and intake of high tannin forages.
Attempts to improve silage quality using tannins have also been reported.