THE EFFECT OF CONDENSED TANNINS IN LOTUS-CORNICULATUS ON PLASMA METABOLISM OF METHIONINE, CYSTINE AND INORGANIC SULFATE BY SHEEP

Fresh Lotus corniculatus containing 27 g extractable condensed tannin (CT)/kg dry matter (DM) and 8 g bound CT/kg DM was fed at hourly inter vals to sheep held in metabolism cages to study the effects of CT on n utrient digestion and on metabolism of methionine, cystine and inorgan ic sulphate in plasma. Polyethylene glycol (PEG) was continuously infu sed into the rumen of half the sheep to remove the effects of CT. Prin cipal measurements in the two groups were plasma irreversible loss (IR L) rate and interconversions of methionine, cystine and inorganic sulp hate using S-35 labelling. CT in Lotus corniculatus had no effects on the apparent digestion of cellulose and minerals, slightly depressed D M, organic matter and hemicellulose digestion and markedly reduced the apparent digestion of N (P < 0.01). The concentration of NH3 and mola r proportions of iso-butyric acid, iso-valeric acid and n-valeric acid in rumen fluid were markedly increased by the PEG infusion (P < 0.01) , whereas total volatile fatty acid concentration and molar proportion s of acetic acid, propionic acid and n-butyric acid were not affected. PEG infusion temporarily increased rumen protozoa numbers. CT greatly increased the IRL of plasma cystine (13.1 v. 7.0 mu mol/min; P < 0.05 ) and reduced IRL of plasma inorganic sulphate (36.8 v. 48.1 mu mol/mi n; P < 0.01) but had no effect on methionine IRL. CT increased transul phuration of methionine to cystine (4.37 v. 1.24 mu mol/min; P < 0.05) , increased cystine entering the plasma from whole-body protein turnov er plus absorption from the small intestine (9.34 v. 5.75 mu mol/min; P < 0.05) and increased cystine flux to body synthetic reactions (11.8 9 v. 5.41 mu mol/min; P < 0.05). CT had no effect on the proportion of methionine total flux transferred to sulphate (0.05 v. 0.06; P < 0.05 ), reduced the proportion of methionine flux transferred to body synth etic reactions (0.68 v. 0.86) and markedly reduced the proportion of c ystine flux transferred to sulphate (0.09 v. 0.27; P < 0.01). It was c oncluded that CT in Lotus corniculatus reduced rumen protein degradati on and markedly increased utilization of plasma cystine for body synth etic reactions.