SULFUR AMINO-ACID-METABOLISM AND PROTEIN-SYNTHESIS IN YOUNG SHEEP FEDRYEGRASS PASTURE AND 2 LOTUS CULTIVARS CONTAINING CONDENSED TANNIN

Groups of sheep were fed either fresh ryegrass pasture, a low condense d tannin (CT) diet (Lotus corniculatus; or a medium CT diet (L. pedunc ulatus) to compare the effects of these feeds on methionine and cystei ne metabolism, because of their significance in wool production, and o n phenylalanine as an indicator of general protein metabolism. Dry mat ter intake (DMI) among groups, ryegrass pasture, Lotus corniculatus, L . pedunculatus, were significantly different, therefore the treatment means for metabolic measurements and wool growth were adjusted by cova riate analysis using DMI. Neither diet nor DMI had any overall effect on phenylalanine concentrations in whole blood or phenylalanine irrevi rible loss rate (IRL). However there were significant (P < 0.001) diet effects on cysteine blood concentrations. Methionine effects parallel ed those of cysteine, with higher concentrations in sheep fed L. pedun culatus relative to pasture fed animals. Sheep fed L. pedunculatus had much higher cysteine and methionine ILRs compared with either the pas ture or L. corniculatus groups. Sheep fed the highest level of condens ed tannin in their diet (l. pedunculatus) had significantly greater ra tes of transsulfuration, cysteine and methionine oxidation. Overall th e results show that CT in L. pedunculatus gives a greater degree of 'p rotection' during digestion for cysteine, methionine and phenylalanine , while L. corniculatus resulted in very little advantage. Condensed t annin effects on wool production are marginal and secondary to whole b ody metabolic influences.