Parasitic helminths of veterinary importance in cattle,sheep and goats on communal farms in the northeastern Free State,South Africa

The purpose of the study was to record and determine intensities, seasonal incidence and distribution of helminth parasites of veterinary importance that occur in cattle, sheep and goats in the northeastern Free State. The study was conducted at Harrismith and Kestell and in Qwa-Qwa from March 2000 to May 2001. Cattle of various breeds (including Bonsmara, Simmentaler and Friesian), Merino sheep and Angora goats were sampled. Faecal samples were analysed using the McMaster and Visser sieve techniques for egg counts and faecal cultures for 3rd-stage nematode larvae identification. Haemonchus and Oesophagostomum were the dominant nematode genera found to be infecting the animals. The socioeconomic status of the farmers in the study area was determined through a questionnaire survey aimed at recording their management strategies. It indicated that 81% of farmers take care of their livestock by feeding them with supplements. The low to moderate faecal egg counts from cattle showed that helminth infections in this region are still under control even though helminthosis seems to be a problem in small-stock, since EPG counts of more than > 1000 were found. Cattle farmers in this region are encouraged to continue with good animal husbandry practices that have ensured that helminth infections rates are kept low. Small-stock farmers are, however, encouraged to control helminth infections in their sheep and goats by anthelmintic treatment.     

Anthelmintic resistance of nematode parasites of small ruminants in eastern Ethiopia: exploitation of refugia to restore anthelmintic efficacy

Faecal egg count reduction tests (FECRT) were conducted in May 2003 to determine the efficacy of anthelmintics used for treatment against nematode parasites in separately managed sheep and goat flocks at Alemaya University in eastern Ethiopia. These tests revealed high levels of anthelmintic resistance to albendazole, tetramisole, the combination of these two drugs, and to ivermectin in the goat flock (predominantly infected by Haemonchus contortus and Trichostrongylus spp.), whereas all drugs were highly efficacious in the sheep flock. A second FECRT confirmed these observations. Following this, a new management system was implemented on the goat flock for a period of 9 months (January-September 2004) in an attempt to restore the anthelmintic efficacy. This involved a combination of measures: eliminating the existing parasite infections in the goats, exclusion from the traditional goat pastures, and introducing communal grazing of the goats with the university sheep flock and livestock owned by neighbouring small-holder farmers. A second series of FECRTs (Tests 3 and 4) conducted 7 months after this change in management, showed high levels of efficacy to all three drugs (albendazole, tetramisole and ivermectin) in the goat flock. This is the first field study to demonstrate that anthelmintic efficacy in the control of nematode parasites of small ruminants can be restored by exploiting refugia.     

Evaluation of anthelmintic properties of extracts from some plants used as livestock dewormers by pastoralist and smallholder farmers in Kenya against Heligmosomoides polygyrus infections in mice

Parasitic nematodes are among the most common and economically important infectious diseases of grazing livestock, especially in small ruminants in the tropics and subtropics in Kenya the control of gastrointestinal nematode infections in sheep and goats is usually made with synthetic anthelmintics but substantial levels of anthelmintic resistance have been recorded. A number of medicinal plants, that may provide possible alternatives, and are used by pastoralists and smallholder farmers in Kenya as deworming agents for their livestock and equines, namely Aframomum sanguineum, Dodonea angustifolia, Hildebrandtia sepalosa, Myrsine africana, Rapanea melanophloeos from Kenya, and Azadirachta indica from Kenya and Malaysia, together with the chemicals embelin and santonin that occur in some of these plants, were evaluated against Heligmosomoides polygyrus in mice. Commercial anthelmintics, namely ivermectin, pyrantel and piperazine, were also investigated, both to validate the mouse model system and to assess efficacy of these drugs against H. polygyrus. Pyrantel and ivermectin were highly effective in reducing the numbers of H. polygyrus worms as well as eggs in faeces of the mice, but piperazine had a lower activity. Application of santonin and M. africana significantly reduced the number of total worm counts (TWC) but not faecal egg counts (FEC). The use of embelin, R. melanophloeos and A. indica reduced FEC but not TWC. In all cases, however, reductions were well below the a priori level of 70% required for biological significance. A. sanguineum, D. angustifolia and H. sepalosa had no effect on either TWC or FEC. In conclusion, none of the plant preparations had any biologically significant anthelmintic effect in this monogastric host-parasite model system.     

From discovery to development: current industry perspectives for the development of novel methods of helminth control in livestock

Despite the extraordinary success in the development of anthelmintics in the latter part of the last century, helminth parasites of domestic ruminants continue to pose the greatest infectious disease problem in grazing livestock systems worldwide. Newly emerged threats to continuing successful livestock production, particularly with small ruminants, are the failure of this chemotherapeutic arsenal due to the widespread development of anthelmintic resistance at a time when the likelihood of new products becoming commercially available seems more remote. Changing public attitudes with regards to animal welfare, food preferences and safety will also significantly impact on the ways in which livestock are managed and their parasites are controlled. Superimposed on this are changes in livestock demographics internationally, in response to evolving trade policies and demands for livestock products. In addition, is the apparently ever-diminishing numbers of veterinary parasitology researchers in both the public and private sectors. Industries, whether being the livestock industries, the public research industries, or the pharmaceutical industries that provide animal health products, must adapt to these changes. In the context of helminth control in ruminant livestock, the mind-set of 'suppression' needs to be replaced by 'management' of parasites to maintain long-term profitable livestock production. Existing effective chemical groups need to be carefully husbanded and non-chemotherapeutic methods of parasite control need to be further researched and adopted, if and when, they become commercially available. This will require veterinary parasitology researchers from both the public and private sectors to work in close co-operation to ensure 'sustainability' - not only of the livestock industries that they service - but also for their very own activities and enterprises.     

Assessment of anthelmintic resistance in nematode parasites of sheep and goats owned by smallholder farmers in eastern Ethiopia

The anthelmintic resistance status was investigated of nematode parasites of sheep and goats owned by smallholder farmers in communities that received breeding stock from a source where a high level of anthelmintic resistance has been reported. The investigation used the faecal egg count reduction technique, whereby suitable animals within each of eight separate communities were pooled to achieve the numbers required to conduct separate tests for both sheep and goats. Anthelmintics tested were albendazole (ABZ), tetramisole (TET), a combination (ABZ $+$ TET) and ivermectin (IVM), at the manufacturers' recommended dose rates. Results showed that there was no evidence of anthelmintic resistance in nematode parasites of either sheep an goats in any community. This indicates that dilution of resistant parasites imported with introduced breeding stock, and the low selection pressure imposed by the smallholder farmers themselves, has prevented anthelmintic resistance from emerging in nematode parasites of small ruminants in these communities.     

Ovine helminthosis, a major health constraint to productivity of sheep in Ethiopia

Small ruminants represent an important component of the Ethiopian livestock production system, providing 12% of the value of livestock products consumed at the farm level and 48% of the cash income generated. Ethiopia is second in Africa and sixth in the world in terms of sheep population. The country has, however, benefited little from this enormous resource owing to a multitude of problems, disease being the most important. Disease alone accounts for mortalities of 30% in lambs and 20% in adults. Productivity losses attributable to helminth parasites are often substantial. A loss of US $ 81.8 million is reported annually due to helminth parasites. In a country confronted with challenges of an ever-rising human population and food shortage, such enormous losses caused by helminth parasites, 'the silent predators', are intolerable. Therefore, helminth control should receive special attention in poverty reduction strategies through improved productivity of livestock if the present and future challenges of food shortage are to be addressed. Productivity loss due to helminth infections can be substantially reduced through implementation of effective disease control strategies, which require an understanding of the epidemiology and ecology of parasites and parasitic infections under local conditions. This paper reviews extensive evidence demonstrating that helminthosis is a major constraint to productivity of sheep in Ethiopia. It also discusses epidemiology and ecology of major helminth parasites in the country and suggests strategies for improved control in various agro-ecological zones and production systems.     

Targeted selective treatment for worm management-How do we sell rational programs to farmers?

Seriously escalating global anthelmintic resistance in gastrointestinal nematodes of small ruminants has spawned a variety of alternatives to anthelmintics for worm management, based on the need for sustainable Integrated Parasite Management (sIPM). Pivotal to the sIPM approach is the concept of refugia, the proportion of a given parasite population that escapes exposure to control measures. By balancing drug applications with the maintenance of refugia, the accumulation of anthelmintic resistance alleles in worm populations can be considerably delayed, while still providing good levels of control. The over-dispersed nature of parasitic infections provides an opportunity to achieve this balance, by targeting treatments to the members of a flock or herd that are least tolerant to nematode infection. However, implementation of this strategy has only recently become feasible, with the development of the FAMACHA((c)) system for clinical evaluation of anaemia due to haemonchosis. Subsequently, the use of milk yields has proven an effective indicator in dairy goats infected predominantly with nematodes other than Haemonchus contortus. In addition, short-term weight changes and perhaps also body condition scoring may provide indices of parasitism, permitting the rapid identification of animals likely to benefit from treatment. However, sIPM and refugia-based approaches are more complex than whole-flock treatments in conventional programs, and adoption by farmers is most likely where the theoretical basis is understood. As close communication with informed advisors is generally limited, there is a danger that sIPM will remain a theoretical concept without alternative modes of communication. The development of computer-based decision support programs, which use epidemiological, seasonal and clinical information to provide recommendations for specific situations, should be accorded high priority in the future development of worm management systems.     

Anthelmintic drug resistance in the UK

The term 'anthelmintic drug resistance' describes the heritable ability of some nematode parasites to survive treatment with anthelmintic drugs at the recommended therapeutic dose levels. Genes for resistance appear to be present in many of the important pathogenic nematodes of ruminants and horses. Under intensive management systems, where heavy reliance is placed on anthelmintic drugs for worm control, the selection of resistant genotypes may result in increased reports of the drugs failing to control the nematode populations against which they are aimed. Anthelmintic resistance has been reported from many parts of the world, and in some countries multiple drug-resistant strains have emerged. In the UK, recent investigations indicate an increasing level of resistance to benzimidazoles among nematodes of sheep and horses. The incidence, diagnosis, epidemiology and implications of anthelmintic resistance are discussed.     

Prospects for biological control of nematode parasites of ruminants

Control of nematode parasites in ruminants is directed almost exclusively at the parasitic stage in the host using conventional anthelmintic therapy. However, to complete their life cycle, parasites have to develop through a series of free-living stages on pasture. It is within this environment that there is a vast range of cohabiting micro-organisms, some of which are known to infect or prey on nematodes. These include bacteria, protozoa, viruses and fungi. To date, most interest has been focused on those organisms producing chemical toxins which have been developed as anthelmintics, e.g. Streptomyces/avermectins. Yet the potential of predacious and nematoxic fungi and bacteria for the biological control of nematode parasites of livestock remains largely untapped. These organisms may well offer a cheaper and more sustainable approach to reducing the impact of parasitism in livestock.     

Tactical treatment with copper oxide wire particles and symptomatic levamisole treatment using the FAMACHA(©) system in indigenous goats in South Africa

Haemonchosis is considered to be the most economically important gastrointestinal disease of small ruminants in the tropics and subtropics. However, chemical anthelmintics, which were the mainstay of control, have been compromised by a high prevalence of resistance worldwide. Copper oxide wire particles (COWP) have been shown to have anthelmintic effects, but few studies have examined their use under field conditions. The use of COWP was therefore evaluated as a tactical anthelmintic treatment in indigenous goats raised under communal farming conditions in Bergville, KwaZulu-Natal Province, South Africa. At the beginning of the summer rainfall season (October 2007), the faecal egg counts of 172 female goats belonging to 15 farmers were determined and this sampling continued every four weeks until the second week of January 2008. The goats within each of the 15 herds were ranked according to their faecal egg counts for this week. The goats were sequentially paired off within each ranking starting with those goats with the highest counts. One goat from each pair was randomly allocated to a treated or control group. Two weeks later, a 4 g COWP bolus was randomly administered to each goat in the treated group. Faecal egg counts were carried out on the goats two weeks following treatment, and the sampling of the goats then proceeded every four weeks until October 2008. Except for the six-week period prior to the administration of the COWP, the goats were examined according to the FAMACHA^© system and symptomatically treated with 12 mg/kg levamisole when anaemic. The percentage reduction in faecal egg count due to the COWP treatment was 89.0%. Mean pre- and post-treatment faecal egg counts for the COWP-treated group (n = 73) were 2347 eggs per gram of faeces (epg) and 264 epg, respectively. The corresponding values for the untreated controls (n = 66) were 2652 epg and 2709 epg. The prevalence of Haemonchus spp. larvae in pre- and post-treatment faecal cultures was 72% and 46%, respectively. Symptomatic anthelmintic treatments in combination with mid-summer tactical treatments with COWP appear to be useful strategies for the control of Haemonchus contortus in indigenous goats in this farming system and this approach could have application in other similar agro-ecological zones.     

Global perspectives on nematode parasite control in ruminant livestock: the need to adopt alternatives to chemotherapy,with emphasis on biological control

Effective, sustainable control of nematode parasites of grazing livestock is becoming evermore challenging and difficult. This is largely due to two contrasting issues. One is the rapid escalation of resistance to anthelmintic drugs, which is arguably the greatest problem now facing the small ruminant industries worldwide. Secondly, there is the increasing trend towards organic farming, in which there is prohibition of the prophylactic use of all chemical compounds. Livestock producers urgently need non-chemotherapeutic alternatives in parasite control. Researchers have responded to this challenge and a variety of quite different approaches have been the subject of intense investigation in many countries for several decades now. These vary in relation to their stage of development for on-farm use, their utility, and their applicability across the spectrum of grazing livestock enterprises throughout the world. One relatively recent innovation is the biological control approach to nematode parasites. This has now reached the stage of commercialization. This review focuses on these issues and provides an overview of the possible ways in which the biological control of nematode parasites could be employed in grazing ruminant livestock systems worldwide.     

Anthelmintic resistance in equine parasites - detection, potential clinical relevance and implications for control

During the past two decades anthelmintic resistance in equine parasites has been found in the group of small strongyle species (cyathostomins) and in the ascarid species Parascaris equorum. The ubiquitous nature and possible severe consequences of disease with these nematodes make them the prime targets of current worm control programmes. Traditional control strategies mainly rely on the strategic application of anthelmintics, currently represented by three major drug classes: benzimidazoles (BZ), the tetrahydropyrimidine pyrantel (PYR) and macrocyclic lactones (ML). Following decades of routine and frequent anthelmintic applications, many cyathostomin populations on horse farms in industrialised countries must be considered as resistant to BZ anthelmintics. However, to date no published cases of cyathostomin disease specifically associated with anthelmintic resistance were reported. Possibly this is due to the generally subclinical and unspecific symptoms associated with cyathostomin infections. Nevertheless, exclusive reliance on the ML drug class may increase the threat of clinical disease due to drug-resistant cyathostomins. More recently, P. equorum has been reported as having developed resistance against ivermectin and moxidectin, two representatives of the ML-class. These anthelmintics are currently the most frequently used drug class in horses. This nematode species is mainly found in foals and in younger horses due to the development of immunity following exposure to infection. Infection with P. equorum can result in clinically drastic consequences such as obstruction and/or penetration of the small intestine, the latter usually leading to death. In conclusion, on horse farms the efficacy of anthelmintic treatments should be examined routinely for each drug class. Several factors can influence the rate at which anthelmintic resistance develops; high frequency of treatment being one of the most important. Modern control strategies should therefore attempt to significantly reduce anthelmintic treatments. Several pasture and farm management practices found to be negatively associated with nematode and anthelmintic resistance prevalence will be discussed in the review presented here.     

Treatment vs non-treatment of helminth infections in cattle: defining the threshold

Helminth infections are an important cause of lost productivity in livestock world-wide, often necessitating anthelmintic treatment. However, a large part of the anthelmintics are used indiscriminately because the parasite levels are too low to justify treatment or because the treatments are not correctly programmed, resulting in undertreatment or overtreatment. The objective of this paper is to discuss possible thresholds for anthelmintic treatment of some of the more important helminth infections in livestock, i.e. gastrointestinal nematodes, lungworms and liver fluke, to promote a more appropriate use of anthelmintics. When possible, a distinction is made between therapeutic thresholds, production-based thresholds and preventive thresholds. A "therapeutic threshold" is intended to identify (an) animal(s) with parasite levels that necessitate immediate treatment. The therapeutic threshold is basically the diagnosis of clinical disease, and can be determined relatively easily for the parasites discussed in this paper. A "production-based threshold" is intended to measure the effects of sub-clinical parasitism on productivity parameters, such as weight gain and milk yield, before clinical disease occurs. Finally, a "preventive threshold" is meant to predict future infection levels, to enable the application of appropriate control measures.     

Ethnoveterinary plant preparations as livestock dewormers: practices, popular beliefs, pitfalls and prospects for the future

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.     

Common helminth infections of donkeys and their control in temperate regions

Roundworms and flatworms that affect donkeys can cause disease. All common helminth parasites that affect horses also infect donkeys, so animals that co‐graze can act as a source of infection for either species. Of the gastrointestinal nematodes, those belonging to the cyathostomin (small strongyle) group are the most problematic in UK donkeys. Most grazing animals are exposed to these parasites and some animals will be infected all of their lives. Control is threatened by anthelmintic resistance: resistance to all 3 available anthelmintic classes has now been recorded in UK donkeys. The lungworm, Dictyocaulus arnfieldi, is also problematical, particularly when donkeys co‐graze with horses. Mature horses are not permissive hosts to the full life cycle of this parasite, but develop clinical signs on infection. In contrast, donkeys are permissive hosts without displaying overt clinical signs and act as a source of infection to co‐grazing horses. Donkeys are also susceptible to the fluke, Fasciola hepatica. This flatworm can be transmitted, via snails and the environment, from ruminants. As with cyathostomins, anthelmintic resistance is increasing in fluke populations in the UK. A number of the anthelmintic products available for horses do not have a licence for use in donkeys, and this complicates the design of parasite control programmes. As no new equine anthelmintic classes appear to be near market, it is important that the efficacy of currently effective drugs is maintained. It is important that strategies are used that attempt to preserve anthelmintic efficacy. These strategies should be based on the concept that the proportion of worms in a population not exposed to anthelmintic at each treatment act as a source of ‘refugia’. The latter is an important factor in the rate at which resistance develops. Thus, it is imperative that parasite control programmes take into account the need to balance therapy to control helminth‐associated disease with the requirement to preserve anthelmintic effectiveness.     

Managing anthelmintic resistance: Is it feasible in New Zealand to delay the emergence of resistance to a new anthelmintic class?

The recent registration in New Zealand of the first new class of broad-spectrum anthelmintic, for use against nematode parasites of ruminants, in nearly three decades has raised the possibility that parasite management practices could be improved to minimise the emergence of resistance to the new drug. A review of knowledge pertaining to the selection of anthelmintic resistance in nematode parasites of sheep highlights a number of management practices which could be altered to achieve this.

A number of previously common practices such as whole-flock treatment of adult ewes around lambing, and treatment of lambs as they are moved onto pastures with low parasite contamination have been clearly identified as high risk for selecting resistant parasites. Once high-risk practices have been identified steps can be taken to either eliminate their use or mitigate the associated risk. Much of the focus on the management of resistance around the world is on the retention of susceptible genotypes in refugia. While approaches to retaining unselected parasites are likely to vary around the world, empirical studies indicate that the practice is likely to be effective at slowing the development of resistance. The challenge for farmers and advisors will be to strike a balance between retaining sufficient susceptible para-sites to usefully delay the development of resistance while not unduly compromising animal performance and farm profitability. The merits of combining different classes of anthelmintic in order to slow the development of resistance remains somewhat contentious in some countries. However, the attributes of oral anthelmintics are such that they seem likely to meet most, if not all, of the criteria for combinations to be highly effective at slowing the build-up of resistance in nematode parasites.

It is evident that considerable progress has been made in understanding the factors involved in selecting anthelmintic-resistant nematodes since the last broad-spectrum anthelmintic class was released in the early 1980s. Therefore, it should be possible to manage a new class of anthelmintic in such a way as to significantly extend its effective life. The challenge is likely to be in convincing farmers of the merits of adopting such pro-active strategies.     

Anthelmintic efficacy and dose determination of Albizia anthelmintica against gastrointestinal nematodes in naturally infected Ugandan sheep

Weight loss, stunted growth, and death caused by gastrointestinal parasites are major constraints to livestock productivity, especially in tropical and developing countries where regular use, and misuse, of anthelmintics has led to nematode resistance. Albizia anthelmintica Brong. (Fabaceae) is traditionally employed throughout East Africa to treat helminth parasitosis in livestock. Reported efficacy has varied from 90% against mixed nematodes to just 19% against Haemonchus contortus alone. The objective of this study was to assess the anthelmintic effect of A. anthelmintica against naturally occurring infections of mixed gastrointestinal parasites, and to establish an effective treatment dose, in sheep under pastoral field conditions of northern Uganda. A. anthelmintica bark was collected and prepared according to local custom and packed into gel capsules. Fifty-five young female local mixed-breed lambs were randomly assigned to six groups, including a positive control group that received levamisole (synthetic anthelmintic) and a negative control group that received no treatment. Following the World Association for the Advancement of Veterinary Parasitology (WAAVP) dose determination guidelines, the other four groups were treated with varying doses of A. anthelmintica. Statistical analyses (using generalized linear models) were performed to assess treatment effect. There was a significant treatment (group) effect on parasite egg/oocyte counts per gram (EPG) for nematodes, but not for coccidia. The most effective dose against nematodes (0.8g, 58.7mg/kg) closely approximates what is usually given by traditional healers, 0.9g/adult sheep. It provided major and significant reduction in EPG as compared to the negative control. Anthelmintic efficacy was estimated using percent faecal egg count reduction (FECR). Other than the positive control, animals in the standard dose group showed the greatest decline in shedding of nematode eggs, with an FECR of 78%. This study indicates that A. anthelmintica holds potential as part of an integrated management plan for the control of helminths in developing countries.     

Effect of anthelmintic treatment on the performance of Awassi sheep in Iraq

Studies are reported on the effect of anthelmintic treatment on the body weight gain and wool growth of ewes with subclinical helminth infections. The parasites involved were Fasciola gigantica and Ostertagia spp., together with some Haemonchus contortus, Trichostrongylus spp., and Dictyocaulus filaria. In 1 group, 5 sheep, which were treated twice with tetramisole at an interval of 4 weeks to remove gastro-intestinal nematodes and lungworms, showed an increase of 41% in weight gain and 3.2% in wool growth compared with an untreated group. Another group, which was treated with both tetramisole and rafoxanide to remove nematode and fluke infections, had a 143% increase in weight gain and 81% in wool growth compared with the control.     

Anthelmintic resistance in New Zealand: A perspective on recent findings and options for the future

A recent national survey on anthelmintic resistance in cattle and sheep in New Zealand indicated that the magnitude of the problem has increased from very low levels only a few years ago to disturbingly high levels now. There is a particular problem with multiple resistance to all three action families of anthelmintic currently available in Ostertagia (= Teladorsagia) spp in sheep, and to both macrocyclic lactones (ML) and benzimidazoles in Cooperia spp in cattle. The prevalence and extent of resistance indicate that all cattle farmers and most sheep farmers should now be using a combination anthelmintic on most occasions just to achieve effective control of all parasites. Despite this, the presence of resistant parasites has generally not been appreciated by the majority of affected farmers, possibly because most have not formally tested to determine the resistance status of nematodes on their farms.

Anthelmintics will remain the cornerstone of gastrointestinal nematode control in sheep and cattle for the foreseeable future but to ensure their continued effectiveness farmers need to be constantly aware of the need to maintain adequate reservoirs of unselected nematodes, i.e. worms in refugia, to minimise the expansion of the resistant population. High-risk practices in relation to selection of resistance need to be identified and avoided or at least their use limited. These include: treating adult animals where there is no identified need, moving newly- treated animals onto ‘clean’ pasture, and failing to effectively quarantine-drench bought-in animals. None of these are new concepts but many have not been adopted or practised. In particular, sheep farmers should endeavour to avoid treating ewes pre-lambing with long-acting anthelmintics. Farmers needs to negotiate a balance between achieving good parasite control and the sustainability of their control options.     

Evaluation of efficacy expectations for novel and non-chemical helminth control strategies in ruminants

The interest in novel methods of controlling helminth infections in ruminants is driven primarily by the development of parasite resistance to currently available anthelmintics. While the purpose of anthelmintics is to achieve high efficacy, i.e. >90% reduction of adult and/or larval parasites in the target host animal, the purpose of novel parasite control methods is rather to assist in maintaining parasite infections below the economic threshold. The ability to maintain parasite levels below the economic threshold is related not only to the efficacy of the control method, but also to the epidemiology of the parasites, climatic conditions, the livestock management program, and integration in a sustainable parasite control program. Because of this fundamental difference, novel parasite control methods need to be evaluated using efficacy criteria different from that adopted for anthelmintics. Although the efficacy of novel parasite control methods may be demonstrated in classic dose-confirmation studies, the impact on livestock production parameters can only be evaluated when tested on-farm. In this paper, the rationale for evaluating novel methods differently from anthelmintics is reviewed, potential performance expectations are presented, and four novel parasite control methods (vaccines, nematophagous fungi, condensed tannins, and immunonutrition) are assessed based on the potential performance criteria.