Effects of condensed tannins inLotus pedunculatuson its nutritive value for sheep. 2. Nitrogenous aspects

Abstract

SummaryFourteen young wether sheep were fed freshly cutLotus pedunculatusas a sole diet to examine the effects of condensed tannins (CT; 55 g/kg lotus DM) on nitrogenous aspects of digestion. The experiment was carried out indoors at Palmerston North, New Zealand over 32 days with one group of sheep receiving an intraruminal infusion of polyethylene glycol (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 increase the flow of feed nitrogen (N) to the abomasum despite a 12% reduction in DM intake of the Tannin sheep. Rumen microbial N turnover rate was slower in Tannin animals than in those receiving PEG (1·86v. 2·63/day) but microbial N flux to the abomasum was similar in both treatments. The proportion of N intake disappearing from the rumen was lower in 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 negated 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 blood were similar for both groups, but Tannin sheep had lower plasma urea concentrations, a more rapid plasma urea turnover rate and a higher irreversible loss than those receiving PEG. Growth hormone concentrations in plasma were similar for both treatments.