EFFECT OF CONDENSED TANNINS IN LOTUS-CORNICULATUS ON THE NUTRITIVE-VALUE OF PASTURE FOR SHEEP

The extent to which condensed tannins (CT) in Lotus corniculatus were able to affect protein degradation and the nutritive value of pasture were evaluated at Palmerston North, New Zealand in 1992 in an indoor f eeding trial with sheep and using in vitro incubations. The feeding tr ial involved three groups of seven young wether sheep held indoors in metabolism crates for the 32-day experimental period with one group fe d freshly cut ryegrass/clover pasture (Pasture group) whilst the other two groups received a mixture of c. 37% freshly cut Lotus corniculatu s and 63% pasture (dry matter (DM) basis). One of the latter groups wa s given twice daily oral drenches of polyethylene glycol (PEG) to bind with and remove the effects of the CT (PEG group) whilst the remainin g sheep (Tannin group) were not drenched. Intakes of sheep given the m ixed diets were constrained to that of the pasture group. The CT conce ntration in the lotus was 26.1 g/kg DM so that the mixed diets contain ed c. 10 g CT/kg DM. Effects of CT on digestion and sheep performance were minimal. Apparent digestibility of N was lower in the Tannin grou p (76.4%) than PEG (79.8%) or Pasture (79.4%) sheep (P < 0.001), but t here were no differences in DM digestibility (75%) or wool growth from mid-side patches. Rumen ammonia and soluble protein concentrations ap peared to be similar in PEG and Tannin sheep and volatile fatty acid ( VFA) concentrations were similar in all groups (100 mmol/l). For incub ations in vitro, several ratios of Locus corniculatus:pasture were use d to determine the effects of CT on precipitation of soluble proteins and the net yield of ammonia and gas with and without PEG. Homogenates of Lotus corniculatus leaves and pasture showed that 50% of soluble p rotein was precipitated by 1.3% CT in homogenate DM and there was a su bstantial decrease in in vitro degradation to ammonia when lotus leaf accounted for 33% or more of DM with pasture. This work emphasises the need for caution when extrapolating from in vitro to the in vivo situ ation and suggests that 1% CT from Lotus corniculatus may be insuffici ent to affect the nutritive value of fresh forages for sheep.