Abstract
Plants containing condensed tannins (CT) may have potential to control gastrointestinal nematodes (GIN) of cattle. The aim was to investigate the anthelmintic activities of four flavan-3-ols, two galloyl derivatives and 14 purified CT fractions, and to define which structural features of CT determine the anti-parasitic effects against the main cattle nematodes. We used in vitro tests targeting L1 larvae (feeding inhibition assay) and adults (motility assay) of Ostertagia ostertagi and Cooperia oncophora. In the larval feeding inhibition assay, O. ostertagi L1 were significantly more susceptible to all CT fractions than C. oncophora L1. The mean degree of polymerization of CT (i.e. average size) was the most important structural parameter: large CT reduced larval feeding more than small CT. The flavan-3-ols of prodelphinidin (PD)-type tannins had a stronger negative influence on parasite activity than the stereochemistry, i.e. cis- vs trans-configurations, or the presence of a gallate group. In contrast, for C. oncophora high reductions in the motility of larvae and adult worms were strongly related with a higher percentage of PDs within the CT fractions while there was no effect of size. Overall, the size and the percentage of PDs within CT seemed to be the most important parameters that influence anti-parasitic activity.
Highlights
The potential of nutraceutical plants for the sustainable control of gastrointestinal nematodes (GIN) in ruminant livestock is still an under-explored area (Hoste et al 2015)
It has previously been reported that larger condensed tannins (CT) polymers in comparison with smaller ones more efficiently inhibit the feeding ability of firststage larvae (L1) of Ostertagia ostertagi and Cooperia oncophora in cattle (Novobilský et al 2013), and the motility of L4 of A. suum and Oesophagostomum dentatum in pigs (Williams et al 2014a, b)
The mean degree of polymerization (mDP) ranged from 5·3 to 12·7 and the percentages of different tannin types covered almost the full range: 1–99% of PD and 4·3–95·6%
Summary
The potential of nutraceutical plants for the sustainable control of gastrointestinal nematodes (GIN) in ruminant livestock is still an under-explored area (Hoste et al 2015). The CT subunits are commercially available as pure flavan-3-ols and CT that differ in subunit composition can be extracted and purified from various plant sources. This approach is much faster than attempting to separate the different CT groups from a single plant source, such as sainfoin or Lotus sp., where they occur as complex mixtures. This approach can be used to overcome constraints in CT structures imposed by biosynthesis, especially for investigating differences in cis/transstereochemistry, which varies greatly between plant species (Porter, 1988). The CT contents in the earlier study of bovine nematodes ranged from 3 to 60 g CT/100 g fraction (Novobilský et al 2013), and CT have been sparsely investigated in cattle as compared with small ruminants
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