EFFECTS OF CONDENSED TANNINS IN LOTUS-PEDUNCULATUS ON ITS NUTRITIVE-VALUE FOR SHEEP .2. NITROGENOUS ASPECTS

Fourteen young wether sheep were fed freshly cut Lotus pedunculatus as a sole diet to examine the effects of condensed tannins (CT; 55 g/kg lotus DM) on nitrogenous aspects of digestion. The experiment was carr ied out indoors at Palmerston North, New Zealand over 32 days with one group of sheep receiving an intraruminal infusion of polyethylene gly col (PEG; 100 g/day) to preferentially bind CT (PEG group) so that the lotus was essentially 'CT-free'. The other sheep, not given PEG, were termed the 'Tannin' group. The principal effects of CT were to increa se the flow of feed nitrogen (N) to the abomasum despite a 12% reducti on in DM intake of the Tannin sheep. Rumen microbial N turnover rate w as slower in Tannin animals than in those receiving PEG (1.86 v. 2.63/ day) but microbial N flux to the abomasum was similar in both treatmen ts. The proportion of N intake disappearing from the rumen was lower i n Tannin (0.13) than in PEG sheep (0.26) and the N digestibility was 0 .67 and 0.81 for the respective treatments (P < 0.001). The beneficial effects of CT in reducing rumen degradation of feed protein were nega ted in part by a reduction in fractional absorption of amino acids (AA ) from the small intestine. Fractional absorption of essential AA was 0-66 in Tannin and 0.79 in PEG sheep; values for non-essential AA were 0.59 in Tannin and 0.73 in PEG groups. Amino acid concentrations in b lood were similar for both groups, but Tannin sheep had lower plasma u rea concentrations, a more rapid plasma urea turnover rate and a highe r irreversible loss than those receiving PEG. Growth hormone concentra tions in plasma were similar for both treatments.