Identification and validation of bioactive plants for the control of gastrointestinal nematodes in small ruminants

The search for bioactive plants which can be used as non-conventional anthelmintics (AHs) has received considerable attention in recent times because of the increasing, worldwide development of resistance to chemical anthelmintics in worm populations. However, scientific evidence to validate the use of plants remains limited. The criteria required for the scientific validation of phytomedicine and nutraceuticals are similar to those expected for chemical anthelmintics: definition and quality, efficacy, identification of side-effects. However, the methods of investigation need to take into account i) the variability in bioactive compounds in the natural resources, ii) the mode of distribution to animals and iii) the potential anti nutritional and side-effects of some bioactive compounds and the possible occurrence of regulative mechanisms in the hosts. These points are critically discussed, in particular by reference to the example of tannin rich plants with anthelmintic properties from both temperate and tropical regions.