Effects of condensed tannins in Lotus pedunculatus on its nutritive value for sheep. 1. Non-nitrogenous aspects

Summary

Lotus pedunculatus was grown under high fertility conditions and its nutritive value was determined in a feeding trial with sheep at Palmerston North, New Zealand in 1989. The condensed tannins (CT) accounted for 5·5 % of lotus dry matter (DM) and its effect on digestion was evaluated by giving an intraruminal infusion of polyethylene glycol (PEG) to six of the sheep (PEG group). PEG preferentially binds with CT so that the lotus becomes essentially CT-free.

The experiment was carried out with 14 sheep (six PEG and eight ‘Tannin’) held in metabolism crates 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%, and the digestibility of fibre was not affected by CT. Infusion of PEG increased rumen concentrations of NH3 and volatile fatty acids ( P < 0·001) 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 libitum, 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 end 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 outflow rate, which suggests a slower rate of digestion in the rumen. Growth rate and wool production were similar for sheep on both treatments. 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.