Effects of condensed tannins on established populations and on incoming larvae of Trichostrongylus colubriformis and Teladorsagia circumcincta in goats

Summary

The use of tanniferous plants or tannins represents one alternative approach to the
control of gastrointestinal parasites in ruminants but most data have been obtained in sheep. The
current study was therefore performed in goats with two objectives: firstly, to investigate the effects
of condensed tannins (CT) on adult populations of Trichostrongylus colubriformis and Teladorsagia
circumcincta; secondly, to examine their effects on the establishment of infective larvae of these
two species. In experiment 1, two groups of kids were infected with 6 000 L3 of T. colubriformis
and 6 000 L3 of T. circumcincta. After 7 weeks, quebracho extracts were administered per os for
8 days to one group. A comparable group which did not receive tannins was included as the control.
The kids were slaughtered on week 11. Parasitological and pathophysiological parameters were
measured weekly. Worm counts were assessed and mast cells, globule leukocytes and eosinophils
were counted in the abomasal and intestinal mucosae. Tannin administration was associated with a
decrease in egg excretion, and a decrease in female fecundity, but with no changes in worm numbers.
These changes were associated with an increased number of intestinal mast cells. In experiment
2, 24 goats were used according to a 2 2 factorial design, depending on infection and tannin
administration. Two groups were either infected with 6 000 L3 of T. colubriformis or T. circumcincta.
Within each group, the goats were either drenched or undrenched with tannin extracts.
Pathophysiological parameters were measured weekly. Twelve days after the cessation of tannin
administration, the goats were slaughtered. Worm counts and female worm fecundity were determined.
Tannin consumption was associated with a significant reduction (P < 0.001) of Trichostrongylus
populations and a close to significant reduction for Teladorsagia. No effect on fecundity
was observed. Our results (1) confirm the consequences of condensed tannins on nematodes in goats
as in sheep and (2) indicate divergent effects depending on the parasitic stage exposed to the condensed
tannins.