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In vitro and in vivo studies were conducted to determine possible direct anthelmintic
effects of condensed tannins towards different ovine gastrointestinal nematodes. A
larval development/viability assay was used to investigate the effect of a condensed
tannin extract (Quebracho) towards larvae of Haemonchus contortus, Teladorsagia circumcincta
and Trichostrongylus vitrinus. The development to infective larvae and their viability
was assessed in all three species and LD 50 values were calculated. The presence of
Quebracho extract in the cultures decreased the viability of L3 in all species; the
LD 50 were not significantly different for the different species. Forty-eight sheep
were allocated to one of eight groups and were infected with a single dose of either
4000 L3 H. contortus (groups 1 and 2) or 5000 L3 T. colubriformis and 5000 L3 Nematodirus
battus simultaneously (groups 3-6) or 10,000 L3 of T. circumcincta (groups 7 and 8).
From day 28 until day 31 of the experiment, sheep infected with the intestinal species
were drenched with Quebracho extract at 4, 8 or 16% w/w of food intake, or remained
as undrenched controls; sheep infected with the abomasal species were either drenched
with Quebracho extract at 8% w/w of food intake or remained as undrenched controls.
All sheep were slaughtered 4 days after the end of the drenching period. Sheep infected
with the intestinal species and drenched with 16% w/w Quebracho had lower FEC compared
to sheep drenched with 8% w/w (P<0.05), which in turn were lower than in sheep either
drenched with 4% Quebracho or which remained undrenched (P<0.05). The lowest intestinal
worm burden was recovered from sheep drenched with 8% w/w Quebracho extract (P<0.05).
The administration of Quebracho extract at 8% of food intake for 3 days did not affect
FEC or worm burdens in sheep infected with the abomasal species compared to controls.