THE EFFECT OF CONDENSED TANNINS IN LOTUS-PEDUNCULATUS ON THE SOLUBILIZATION AND DEGRADATION OF RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE (EC-4.1.1.39 - RUBISCO) PROTEIN IN THE RUMEN AND THE SITES OF RUBISCO DIGESTION

Three experiments were undertaken to determine the effect of condensed tannin (CT) in Lotus pedunculatus (45-55 g extractable CT/kg DM) on t he digestion of the principal leaf protein, ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39; Rubisco; fraction 1 leaf protein), In two of the experiments Lotus pedunculatus was fed to sheep, with one group r eceiving a continuous intraruminal infusion (per fistulum) of PEG (mol ecular weight 3500) to bind and inactivate the CT (PEG group), The oth er group, which did not receive PEG, was termed the control sheep (CT acting), Expt 3 involved ill vitro incubations of Lotus pedunculatus i n buffered rumen fluid, with and without PEG added, In all experiments the results have been interpreted in terms of the effects of CT on Ru bisco solubilization and degradation, Disappearance of N and Rubisco f rom Lotus pedunculatus suspended in polyester bags in the rumen was us ed as a measure of solubilization, Degradation was defined as the disa ppearance of Rubisco from in vitro incubations of Lotus pedunculatus i n rumen fluid, In Expt 1, CT reduced the digestion of Rubisco in the r umen from 0.96 to 0.72 of intake (P < 0.01), Rubisco digestion in the small intestine was 0.27 of intake in control sheep and 0.04 of intake in PEG sheep. In Expt 2, PEG had no effect on the loss of Rubisco fro m Lotus pedunculatus contained in polyester bags which were incubated in the rumen, hence CT did not affect the solubilization of Rubisco, O bservations in Expt 1 were confirmed by in vitro incubations in Expt 3 , where PEG addition substantially increased the rate of degradation o f plant protein to NH3. Addition of PEG decreased the period of time t aken to degrade 50% of the Rubisco from about 13.8 h to about 3.0 h, I t was concluded that the action of CT reduced the digestion of Rubisco in the rumen of sheep fed on fresh Lotus pedunculatus, and that this was primarily due to the ability of CT to slow its degradation by rume n micro-organisms, without affecting its solubilization. Both fresh-mi nced, and freeze-dried and ground lotus were used for in sacco and in vitro incubations; however, fresh-minced lotus was more suitable for t he evaluation of protein solubilization and degradation in fresh forag es.