GROWTH AND GASTROINTESTINAL NEMATODE PARASITISM IN LAMBS GRAZING EITHER LUCERNE (MEDICAGO-SATIVA) OR SULLA (HEDYSARUM-CORONARIUM) WHICH CONTAINS CONDENSED TANNINS

Two grazing experiments were undertaken to evaluate the effects of sul la (Hedysarum coronarium) which contains condensed tannins (CT) and lu cerne (Medicago sativa), which does not contain CT, on the performance of parasitized and non-parasitized lambs. The work was carried out ne ar Palmerston North, New Zealand in 1992 and 1993. Experiment 1 used l ambs which were either genetically 'conventional' or 'resistant' to ga strointestinal nematodes and which had a naturally acquired heavy para site burden (faecal egg count (FEC) 1300-2500 eggs per gram faeces (ep g)). They were either drenched to remove all the parasites or remained undrenched when allocated to pure swards of either sulla or lucerne f or the 28-day experimental period. Liveweight gains of drenched lambs were higher with sulla (mean 302 g/day) than with lucerne (mean 245 g/ day; P < 0.02) and rates of gain were not reduced (P = 0.10) by geneti c resistance to nematodes. Undrenched lambs had mean faecal egg counts of 1090-2220 epg after 28 days, with higher counts in lambs grazing l ucerne than in those grazing sulla (P < 0.05). Lambs grazing lucerne a lso had a much lower average daily gain (ADG) (mean 50 g/day) than tho se grazing sulla (mean 206 g/day; P < 0.0001). Resistant lambs had red uced (P = 0.07) ADG in the sulla treatment only. In Expt 2, lambs with a relatively low worm burden (average FEC 250 epg) were either drench ed to remove all worms or dosed with 20 000 Trichostrongylus colubrifo rmis infective larvae and grazed on pure sulla or lucerne swards for 4 2 days. Drenched lambs had a similar liveweight gain (mean 190 g/day) and wool growth when grazing either sulla or lucerne. Undrenched lambs grazing sulla had a greater ADG (mean 129 g/day) than those grazing l ucerne (mean -39 g/day; P < 0.0001) and a higher rate of wool growth f rom mid-side patches (P < 0.009) and larger wool fibre diameter (P < 0 .05) than those grazing lucerne. Undrenched lambs grazing sulla had lo wer FECs (P < 0.05) on days 14, 21, 35 and 42 than those grazing lucer ne and lower (P < 0.05) Trichostrongylus colubriformis worm burdens at slaughter. Undrenched lambs had less perineal faecal contamination wh en grazing sulla rather than lucerne. Parasite-induced anorexia was ev ident in the lambs grazing lucerne but not in those grazing sulla. The se findings demonstrate that the performance of lambs infected with ne matode parasites can vary substantially when given feeds of a similar chemical composition. The superior performance of lambs grazing sulla was probably caused by condensed tannins, which decrease protein degra dation in the rumen and can increase post-ruminal protein availability .