EFFECT OF CONDENSED TANNINS IN LOTUS-PEDUNCULATUS ON THE NUTRITIVE-VALUE OF RYEGRASS (LOLIUM-PERENNE) FED TO SHEEP

A feeding trial was undertaken in Palmerston North, New Zealand in 199 1, to determine the extent to which condensed tannins (CT) in Lotus pe dunculatus were able to affect the nutritive value of ryegrass (which does not contain CT) for sheep. The trial involved three groups of 11 male cryptorchid sheep held in metabolism crates so that intakes, dige stibilities and nitrogen balances could be measured over a 42-day feed ing period. One group was fed freshly cut ryegrass (Lolium perenne L.) as a sole diet (Grass group) and the other two groups were given a mi xture of about one third freshly cut lotus and two thirds ryegrass (dr y matter (DM) basis). This mixture contained c. 1.8% CT in the DM. One group given the mixed diet was drenched twice daily with polyethylene glycol (PEG; PEG group) to bind and remove the effects of the CT from the diet, whilst those not drenched were designated the 'Tannin' grou p. Intakes of all groups were constrained to that of the Grass group o f sheep. Condensed tannins in the lotus had a major effect on the dige stion of ryegrass. When the forages were immature, apparent digestibil ity of nitrogen (N) was substantially reduced in the Tannin sheep (65. 3%) compared to the PEG (77.5%) and Grass (77.9%) groups (P < 0.001). With mature forages, the respective values were 48.8, 62.5 and 53.7% ( P < 0.01). Rumen ammonia concentrations and plasma urea concentrations were also reduced by CT. Condensed tannins reduced DM digestibility b y 3-7 percentage units (P < 0.05) mainly through the effects on N dige stion. Concentrations of acetate, propionate and butyrate in rumen liq uor were not affected by treatment, but CT reduced the proportions of the minor volatile fatty acids (VFA; isobutyrate, valerate and isovale rate). Treatment did not affect liveweight gain (131-164 g/day), or wo ol growth from mid-side patches, and N retention was not reduced by CT , so that the nutritive value of the forage was maintained despite the reduction in N digestibility. The principal finding was that CT in Lo tus pedunculatus were able to affect the digestibility of both grass a nd lotus when fed together, and that as little as 1.8% of CT in the di etary DM had a substantial effect on rumen function.