Condensed tannins in the genus Leucaena and their nutritional significance for ruminants

Abstract

Condensed tannin (CT) can dramatically reduce the utilisation of protein in ruminants. However, at low levels ( 0.10). Part of the advantageous effect of L. leucocephala (K636) CTs on the delivery of protein post-rumen may be attributed to their weaker ability to bind protein, especially at abomasal pH. On a g/g basis, purified L. leucocephala (K636) CT had approximately half the binding power of L. pallida (CQ 3439), L. trichandra (CPI 46568), Lotus pedunculatus (cv. Maku) and Acacia aneura CTs at pH 5, and no measurable binding at pH 2.5, in vitro. There was also an indication that L. leucocephala CT was better able to release protein between the abomasum and end of the small intestine than L. pallida (CQ 3439) and Acacia aneura CT. L. leucocephala (K636) may be an example of a forage with a CT fraction that stimulates a better than expected supply of protein to ruminants. However, the authors, and others, have been unable to directly link enhanced protein flow to enhanced N retention. It is postulated that this lack of translation is because gains in protein delivery are offset by enhanced losses of endogenous protein due to interactions between CT and proteolytic enzymes and/or the gut wall distal to the rumen. The data indicate a promising future for L, leucocephala (K636) and L. collinsii (51/88) forage in productive feeding systems for ruminants in the tropics. In contrast, L. pallida (CQ 3439) and L. trichandra (CPI 46568), whose protein availabilities are dramatically inhibited by CT, should not be recognised as valuable protein supplements.