Abstract
This study investigated the separate and combined anthelmintic (AH) effects of different phenolic compounds, including condensed tannins and flavonoids, all of which are known to occur in willow leaves, a potentially valuable dry season feed. A range of contrasting model tannins, which span the whole range of willow tannins, were isolated from tilia flowers, goat willow leaves, black currant leaves and red currant leaves. All together, the tested compounds represented the major tannin types (procyanidins and prodelphinidins) and flavonoid types (flavonols, flavones and flavanones). The larval exsheathment inhibition assay (LEIA) was used to assess their in vitro effects on Haemonchus contortus third stage larvae. Arbutin, vanillic acid, and taxifolin proved to be ineffective whereas naringenin, quercetin and luteolin were highly effective at 250 μM concentrations. Procyanidin (PC) tannins tended to be less active than prodelphinidin tannins (PD). Experiments with combinations of tannins and quercetin or luteolin revealed for the first time the existence of synergistic AH effects between tannins and flavonoid monomers. They also provided evidence that synergistic effects appear to occur at slightly lower concentrations of PC than PD. This suggests that the AH activity of condensed tannins can be significantly enhanced by the addition of quercetin or luteolin. This information may prove useful for plant breeding or selection and for designing optimal feed mixtures.
Highlights
Infection of small ruminants with gastrointestinal nematodes (GINs) remains a serious pathological problem across the world affecting animal health, welfare and production, as there is a critically high level of drug resistance (Jackson et al, 2012)
Well-defined tannin types are needed for unravelling the relationships between tannin structures and AH activities
Quercetin and luteolin are widely distributed in plants (Yang et al, 2008; Lopez-Lazaro, 2009) and represent two important flavonoid subgroups, i.e. flavonols and flavones, respectively (Fig. 1), and were chosen for the combination experiments with Condensed tannins (CT)
Summary
Infection of small ruminants with gastrointestinal nematodes (GINs) remains a serious pathological problem across the world affecting animal health, welfare and production, as there is a critically high level of drug resistance (Jackson et al, 2012). These GINs are able to develop resistance to new synthetic (anthelmintic, AH) drugs within a few years (Waller, 2006) and, sustainable livestock farming can no longer rely on deworming with AH drugs. The hypothesis for direct effects of polyphenolic compounds has been substantiated by several in vitro assays against different life-cycle stages (Bahuaud et al, 2006; Novobilský et al, 2011)
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