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The use of medicinal plants for the prevention and treatment of gastro-intestinal parasitism has its origin in ethnoveterinary medicine. Although until recently the majority of the evidence on the antiparasitic activity of medicinal plants was anecdotal and lacked scientific validity, there is currently an increasing number of controlled experimental studies that aim to verify and quantify such plant activity. There are indeed a large number of plants whose anthelmintic activity has been demonstrated under controlled experimentation, either through feeding the whole plant or administering plant extracts to parasitised hosts. However, contrary to traditional expectation, there are also a great number of plants with purported antiparasitic properties, which have not been reproduced under experimental conditions. In this paper, we discuss the source of such inconsistencies between ethnoveterinary wisdom and scientific experimentation. We focus on the strengths and weaknesses of the existing methodologies used in the controlled studies to determine the activity of antiparasitic plants. We discuss issues like the seasonal and environmental variability of the plant composition, and how this can affect their antiparasitic properties and highlight the importance of identifying the mechanisms of action of such plants and the target parasite species. In addition to their antiparasitic properties, medicinal plants may also have anti-nutritional properties, which can affect animal performance and behaviour. For this reason, we emphasise the need for considering additional dimensions when evaluating medicinal plants. We also question whether using similar criteria as those used for the evaluation of anthelmintics is the way forward. We propose that a holistic approach is required to evaluate the potential of medicinal plants in parasite control and maximise their benefits on parasitised hosts. Keywords: bioactive plants, ethnoveterinary medicine, medicinal plants, parasites, ruminants IntroductionFor centuries, medicinal plants have been used to combat parasitism, and in many parts of the world are still used for this purpose. In ethnoveterinary medicine, which draws inspiration from traditional practice, there seems to be a range of plant/s or plant extract suitable for treating almost every parasitic disease of livestock (International Institute of Rural Reconstruction (IIRR), 1994). For example, seeds of garlic, onion and mint have been used to treat animals that suffer from gastro-intestinal parasitism, whereas extracts of the tobacco plant have been used to treat the skin of livestock afflicted with external parasites (Guarrera, 1999). Leaves, dried flowers and oil from Chenopodium ambrosioides, a shrub that originated from Central America and has been distributed around the world, have all been used as anthelmintics since the early 1900s (Guarrera, 1999).Reports from around the world include exhaustive lists of plants that have been reported to have medicinal properties (Hammond et al., 1997;Akhtar et al., 2000;Waller ...

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Gastrointestinal helminth infections remain a major constraint to livestock production globally. This study evaluated anthelmintic efficacy of 7 plants used as dewormers by farmers and pastoralists in Kenya. Thus 3 commercial anthelmintics and 7 plant preparations were tested in lambs infected with 5000 or 3000 L3 Haemonchus contortus in 4 experiments. In the first experiment, ivermectin, levamisole and albendazole were tested in 46 lambs. Seven plant preparations of Hagenia abyssinica, Olea europaea var. africana, Annona squamosa, Ananas comosus, Dodonea angustifolia, Hildebrandtia sepalosa and Azadirachta indica were tested in 151 lambs in 3 experiments. All 3 anthelminitics were highly effective in reducing faecal egg counts (FEC) and total worm counts (TWC) in lambs. Plant preparations had varying levels of crude proteins from 2.6% for O. europaea to 18.4% for A. indica. Compared with controls, no significant reductions in FEC were observed for any of the treated groups either 2 or 3 weeks post-treatment. Lambs treated with A. squamosa and A. comosus were slaughtered 4 weeks post-treatment. No significant differences were observed in mean TWC or number of eggs per female worm between treated animals and the controls. No significant improvements in weight gain were observed in treated lambs.

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Ethnomedicine is an integral part of traditional medical practices in many countries of the developing world. A large proportion of the population uses this form of treatment for primary health care and for the treatment of ailments in their livestock. Livestock is a major asset for resource-poor smallholder farmers and pastoralists throughout the world and internal parasites are recognized by these communities as having an impact on livestock health. Parasitic infections are among those infections that traditional healers confidently treat and against which an enormous variety of remedies exist. Many of these are based on the use of plant preparations. Although various methods have been used for the validation of traditional phytomedical preparations, there is a lack of standardization of these procedures. The present study is aimed at providing an overview of ethnoveterinary deworming preparations, the various methods that have been used in their validation and the future prospects for their use against helminth parasites of ruminant livestock in developing countries, with an emphasis on nematode parasites. Recommendations are made on the procedures that should be followed to conduct in vivo and in vitro assays. Fostering better interaction between traditional healers and scientists is advocated to prevent harmful overexploitation, both of local knowledge and of plant species that may have effects against nematode parasites.

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