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We analyse a scattering problem of electromagnetic waves by a bounded chiral conductive obstacle, which is surrounded by a dielectric, via the quasi-stationary approximation for the Maxwell equations. We prove the reciprocity relations for incident plane and spherical electric waves upon the scatterer. Mixed reciprocity relations have also been proved for a plane wave and a spherical wave. In the case of spherical waves, the point sources are located either inside or outside the scatterer. These relations are used to study the inverse scattering problems.
Plant secondary metabolites (PSM) are widely known for their antinutritional properties; their excessive consumption can detrimentally affect herbivore health and, in some cases, survival. However, a growing body of evidence is suggesting that some classes of PSM may also have some positive effects on herbivores. Such positive effects include the antiparasitic properties of certain PSM and their beneficial consequences on the herbivore's fitness. One of the better-exploited classes of PSM that have been reported with anthelmintic properties is that of the condensed tannins. The consumption of moderate concentrations of condensed tannins has resulted in reduced level of parasitism in sheep and other ruminants. In this paper we discuss the conditions that should be met in order for the positive anthelmintic properties of PSM, and condensed tannins in particular, to be beneficial for parasitised sheep. We also examine whether PSM could have a role in controlling parasitism in ruminants and point out the future research needed to achieve an efficient use of PSM for parasite control.
Metabolizable protein (MP) supplementation can reduce faecal egg count (FEC) in periparturient ewes, thus reducing pasture contamination for their lambs (Houdijk et al. 2006). In addition, lambs grazing on bioactive forage (chicory) had lower FEC than lambs grazing grass/clover (Athanasiadou et al. 2007). Both periparturient MP nutrition and grazing on chicory increase lamb performance but these approaches have been developed and investigated independently. The objective of this experiment was to assess their interactive effects on lamb parasitic status and performance. It was hypothesised that, although beneficial effects of maternal nutrition will be augmented with subsequent grazing on bioactive forage, the magnitude of the latter effect will be higher for lambs from unsupplemented ewes.
The potential antiparasitic effects of chicory (Cichorium intybus ) are currently investigated as an alternative means to control parasitism in organic sheep production systems. Previous studies showed that parasitised lambs grazing on parasite-clean chicory swards had improved growth and lower faecal egg counts (FEC) compared to those grazing on parasite-clean grass pastures (Athanasiadou et al, 2004). The objective of this experiment was to investigate whether chicory can have a role as a potential means to control parasitism in lactating ewes and their lambs grazing on previously parasite contaminated pastures.
Sainfoin (Onobrychis viciifolia) is a Mediterranean forage rich in tannins, which has been shown to reduce the faecal excretion of nematode parasites in goats, when offered as hay supplement (Paolini et al, 2003). The use of conserved forages for parasite control may be preferred when either the climatic or agronomic conditions are not appropriate for the grazing of such forages. The aim of this experiment was to investigate whether the consumption of sainfoin hay could reduce the viability and fecundity of adult gastrointestinal parasites, when offered to parasitised sheep at different time points during the course of a parasitic challenge.
Bioactive forages such as chicory (Cichorium intybus) or tanniferous legume sulla (Hedysarum coronarium), have been reported to lower the parasite intensities or faecal egg counts (FEC) of parasitised ruminants (Waller and Thamsborg, 2004). To our knowledge, there is no report studying the effects of these forages on established worm populations when grazed in combination. This knowledge could guide us towards optimum grazing management using special forage species as de-worming paddocks. The aim of the present study was to use the bioactive forages alone or in combination for a short period to test their effects on established T. circumcincta adult population in sheep. The tested bioactive forages were chicory and sulla, with grass/clover (Lolium perenne/Trifolium repens) providing the control forage.
Nematode egg excretion by periparturient ewes is the main source of infection for their immunologically naïve lambs. It has been shown that periparturient metabolizable protein (MP) supplementation can reduce nematode egg excretion (Houdijk et al, 2003). The latter experiment used a single moderate level of infection, but effects of MP supply on periparturient parasitism may depend on the level of infection. The objective of this study was to investigate the effects of MP supplementation on parasite control, ewe and lamb performance in ewes trickle infected with the abomasal nematode Teladorsagia circumcincta at three different infection levels. We hypothesised that the magnitude of beneficial effects of MP supplementation will be higher at the highest level of infection due to the expected nutrient drain on the host.
Parasitised sheep consuming forages high in condensed tannins (CT) show lower faecal egg counts (FEC) and total worm burden (TWB) compared to those consuming CT free forages (Niezen et al., 1998). This may be due to an indirect effect of CT, through an increase in protein availability; extra protein could improve the host’s ability to mount an effective response towards gastrointestinal parasites, during the expression of the immunity (Coop and Kyriazakis, 1999). However, CT have been also shown to have a direct anthelmintic effect on adult Trichostrongylus colubriformis (intestinal nematode), when they were administered for a short period (Athanasiadou et al., 2000). The objectives of this experiment were i) to elucidate the effects of a continuous intake of CT during the development of a T.colubriformis infection and ii) to test whether these effects are dose dependent.
Under organic regulations, farmers in the uk are allowed to drench periparturient ewes with an anthelmintic drug before returning them to pasture. Although such practice is against the principles of organic farming, it is allowed as it reduces parasite contamination of the pastures and consequently reduces the risk of parasitism in growing lambs. Alternatives to control parasitism, which do not jeopardise the health and welfare of grazing ruminants and also minimise anthelmintic input in organic systems are currently being investigated. Grazing bioactive forages, such as chicory has resulted in a lower level of parasitism than sheep grazing on grass/clover pastures (Marley et al, 2003). The objective of this experiment was to investigate whether grazing on chicory can affect the epidemiology of gastrointestinal parasitism, so that control of sub-clinical parasitism could be achieved without the use of anthelmintics.
Parasitised sheep that consumed bioactive forages, i.e. forages that contain anthelmintic compounds, showed a lower level of parasitism than sheep grazing on grass/clover pastures (Marley et al, 2003). This may be due to direct anthelmintic effects of the bioactive forages or indirect nutritional effects, e.g. mediated through an increase in protein availability. Extra protein could improve the host’s ability to mount an effective response towards gastrointestinal parasites (Coop and Kyriazakis, 1999). The aim of this experiment was to investigate whether a two-week consumption of forages that contain potential anthelmintic compounds, have a direct anthelmintic effect towards i) an established Trichostrongylus colubriformis population and/or ii) incoming T.colubriformis larvae.
Ruminants grazing on forages that contain condensed tannins (CT) have lower parasite burdens compared to those grazing on similar quality, tannin-free forages (Min and Hart, 2003). Evidence from previous grazing studies suggested that chicory, which contains only traces of CT, could also reduce the size of the parasite population carried by ruminants (Hoskin et al. 1999). Such bioactive plants may have direct anthelminthic effect on different developmental stages of the worms or indirect effects through nutritional improvement of host immunity. The purpose of this study was to determine whether short-term grazing of bioactive forages could affect either the established adult population or incoming infective larvae of Teladorsagia circumcincta a common abomasal parasite of sheep. The bioactive species tested were chicory (Chicorium intybus) and the CT-containing plants: lotus (Lotus pedunculatus), sainfoin (Onobrychis viciifolia) and sulla (Hedysarum coronarium).
The consumption of condensed tannins has been associated with reduced faecal egg counts (FEC) and total worm burdens (TWB) in parasitised sheep. This can result from either a direct anthelmintic effect (Athanasiadou et al., 2000) and/or an indirect nutritional effect. Condensed tannins can protect dietary protein from rumen degradation and increase protein availability in the small intestine of the host; this could improve the expression of immunity towards parasites (Coop and Kyriazakis, 1999). The objective of the present study was to investigate the consequences of including a condensed tannin extract in foods of different protein content on the performance and development of immunity in parasitised sheep, during the phases of acquisition and expression of immunity.
The extent of periparturient relaxation of immunity (PPRI) to gastrointestinal nematode parasites is sensitive to metabolisable protein (MP) scarcity but also varies between breeds of sheep (Houdijk, 2008). For example, under ad libitum feeding, Scottish Blackface ewes had a lower extent of PPRI than Greyface ewes (Zaralis et al., 2008). Such between-breed variation in PPRI may not necessarily be associated with genetic resistance per se but could arise from a higher nutrient demand of the more productive Greyface ewes (Houdijk, 2008). This experiment was designed to test the hypothesis that if the extent of PPRI has only a nutritional basis, then the sensitivity of PPRI to MP scarcity will not differ between the breeds when MP feeding is adjusted for between-breed differences in MP demand.