EFFECTS OF CONDENSED TANNINS IN LOTUS-PEDUNCULATUS ON ITS NUTRITIVE-VALUE FOR SHEEP .1. NONNITROGENOUS ASPECTS

Lotus pedunculatus was grown under high fertility conditions and its n utritive value was determined in a feeding trial with sheep at Palmers ton North, New Zealand in 1989. The condensed tannins (CT) accounted f or 5.5% of lotus dry matter (DM) and its effect on digestion was evalu ated by giving an intraruminal infusion of polyethylene glycol (PEG) t o six of the sheep (PEG group). PEG preferentially binds with CT so th at the lotus becomes essentially CT-free. The experiment was carried o ut with 14 sheep (six PEG and eight 'Tannin') held in metabolism crate s indoors and given freshly cut lotus hourly, for 32 days. This paper presents data relating to carbohydrate and mineral digestion, together with aspects of rumen function. Digestibility of lotus DM was 68%, an d the digestibility of fibre was not affected by CT. Infusion of PEG i ncreased rumen concentrations of NH3 and volatile fatty acids (P < 0.0 01) but effects on molar ratios of VFA were inconsistent with time. CT reduced rumen degradation and absorption of sulphur and increased net absorption of both phosphorus and zinc, but other effects on mineral digestion were small. Although the lotus was offered at c. 90% of ad l ibitum, intakes of the tannin sheep began to decline after c. 15 days of feeding and were c. 12% lower than those of the PEG sheep at the en d of the trial (P < 0.05). At slaughter, rumen pool sizes were similar for the two treatments but the Tannin sheep had a lower fractional ou tflow rate, which suggests a slower rate of digestion in the rumen. Gr owth rate and wool production were similar for sheep on both treatment s. It is concluded that the CT in Lotus pedunculatus grown under high fertility conditions had little effect on fibre and mineral digestion but the depression in DM intake reduced its nutritive value for sheep.