Methods of Treatment
One of the reasons why lambs do not grow well is because they have parasitic gastroenteritis or nematodiriasis. Diagnosis may be confirmed by egg counts from faecal samples carried out at a veterinary laboratory. The species of parasite causing the parasitic gastroenteritis can also be determined. In the case of unacceptable levels of egg output, the animals have to be treated with an anthelmintic on the advice of the named veterinary surgeon. The use of the AV class of antheminthics, with the exception of moxidectin, is not acceptable in organic farming due to environmental concerns. Botanical or other alternative dewormers may also be useful (Duval, 1994; ADAS, 1996).
Many factors should be considered before deciding when to dose animals, including age of animals, grazing and dosing history, performance/condition and clinical signs of scour/illness. One of the most practical recommendations to control anthelmintic resistance is the specific targeting of anthelmintic dosing to when animals actually need it (McCoy et al, 2005).
The majority of currently available anthelmintics used to control parasitic nematodes of cattle and sheep belong to only three main groups, the benzimidazoles, imidazothiazoles and the avermectins/milbemycins. The successful implementation of control programmes that limit the development of anthelmintic resistance depends partly on effective detection and monitoring (Taylor et al, 2002).
The faecal egg count reduction (FECR) in faeces is the most widely used method to assess the efficacy of anthelmintics including those that undergo metabolism in the host. The FECRT provides an estimation of anthelmintic efficacy by comparing faecal egg counts of animals before and after treatment (Taylor et al., 2002). Cabaret and Berrag, (2004) show that individual FECR provided reliable evaluation when egg counts are over 300 eggs/gram and when at least 10 animals have been tested.
Copper
Copper oxide wire particles (COWP) have been used recently as an anthelmintic in small ruminants to overcome problems associated with nematode resistance to chemical de-wormers. However, there are risks of copper toxicity. Copper oxide wire particles (COWPs) with low levels of copper (2g) have been shown to be effective in reducing infection of Haemonchus contortus with the effect being enhanced with feed supplementation (Burke et al., 2004). Administration of 4 g COWP to late pregnant ewes may negatively impact multiple-born offspring, but 2 g appears to be safe for production (Burke et al., 2005a). However, studies on Swedish sheep flocks (Waller et al., 2004b) showed there was no significant effect of copper mineral supplement (given at the recommended rate to prevent Cu deficiency) on either established, or developing parasite infections. Burke et al (2005b) showed that there was no adverse effect of COWP on the ability of of the nematode-trapping fungus Duddingtonia flagrans to trap residual larvae after COWP treatment. With fewer eggs being excreted due to the effect of copper on H.contortus, and the additional larval reducing effect exerted by the nematode destroying fungus D.flagrans, it may be expected that the result would be a much lower larval challenge on pasture when these two tools are used together in a sustainable control strategy.
Anti-parasitic plant extracts
Under tropical conditions, a number of anti-parasitic agents extracted from plant materials for the control of parasites in goats have been successful e.g. Citrullus vulgaris for tapeworms, Gliricida sepium and Artocarpus heterophilus for common intestinal worms, and Areca catechu for liver fluke. Alternative forages of Mimosa, Papaya, Leucaena leucocephala, Goava leave Mimisa spp. and Flerningia macrophylla have effects on larvae of Haemonchus in vitro. Strongyle egg counts and coccidial oocyt counts were much lower with goats fed foliage of Leucaena, Jackfruit and Cassava compared with common grasses (Nguyen et al., 2005).
Eighty six plant extracts from sixty plant species were collected in the Ivory Coast on the basis of an ethnobotanical literature (Diehl et al., 2004), a quarter of which showed a high anthelminthic activity. In Nigeria, the extract of Khaya senegalensis has been shown to significantly reduce faecal egg counts (Ademola et al., 2004)
Plant cysteine proteinases, from the fruits or latex of plants such as papaya, pineapple and fig, have high proteolytic activities that are known to digest nematode cuticles, have low toxicity and have been used in traditional medicines against gastrointestinal nematodes for decades. These proteinases constitute strong candidates for alternative treatment of gastrointestinal nematode infections of both humans and animals (Stepek et al., 2004).
Varying ranges of faecal egg reduction of 15%, 28%, 65%, 65% and 100% have been achieved in tropical situations against Haemonchus spp., Trichostrongylus spp., Oesophagostomum spp., Strongyloides spp. and Trichuris spp using extracts of Spondias mombin (also known as hog plum, Spanish plum, gully plum, Ashanti plum and golden apple) (Ademola et al., 2005).
Please see section on withdrawal periods for livestock products following medicinal use