Methods of Control and Prevention
In this section a range of control and prevention approaches are described separately although it is important to appreciate that an integrated approach is required in order to reduce reliance on anthelmintic control.
The control and management issues considered are:
Monitoring and evaluation
With sufficient diversity of cropping and stocking, it is possible to virtually eliminate anthelmintic usage on sheep and cattle farms (Keatinge, 2004), although many farms face significant difficulties, particularly those systems dominated by sheep. The extent to which control can be achieved by management alone, depends on the farming system, with the greatest opportunity for control in the more mixed, or very extensive production systems (ADAS, 2004).
Soil Association (2006) technical guide “Managing internal parasites in organic cattle and sheep” describes the appropriate management and husbandry approaches necessary to reduce the challenge from internal parasites, to minimise anthelmintic intervention, and to safeguard the welfare and productivity of organically managed sheep and cattle.
EU project "Worm Control in Organic Production Systems for Small Ruminants in Europe: Towards the implementation of non-chemical, sustainable approaches" or WORMCOP evaluated of a range of novel control approaches and the developed recommendations for sustainable parasitic control in organic production of sheep and goats. One of the outputs was the leaflet “Controlling worms in organic systems (MOSES)” which summarises five strategies:
• Minimise parasite intake
• Optimise nutrition
• Select resistant/resilient animals
• Ensure monitoring
• Select anthelmintics on proven efficacy
The full leafet can be obtained from http://www.wormcops.dk/publications/reports/Leaflet_P5.pdf
The object of any control programme is to prevent contact between the host and the infective stage of the helminths. This may be achieved by using anthelmintic drugs to prevent or limit the contamination of pasture by ewes (during the periparturient egg rise) and lambs prior to June, or by avoiding the grazing of pasture after June where contamination has occurred and larval populations are likely to be high. However, the use of prophylactic anthelmintics is restricted under organic standards (Defra, 2006), so the emphasis has to be on the avoidance of grazing contaminated pastures (Connan, 1997).
On conventional farms where alternate grazing is limited, such as many upland and hill farms, control with prophylactic anthelmintics is often the only method available. On these farms the ewes are usually wormed during the fourth month of pregnancy to eliminate most of the worm burden at this time, including arrested larval stages. As these ewes may ingest over-wintered larvae, the treatment is often repeated within one month of lambing. Lambs are treated at weaning and, where 'safe' pasture is not available for these lambs, treatment is repeated once or twice depending on stocking density (Armour and Coop, 1991).
Some upland farms may be able to graze cattle alternately with sheep on an annual basis to reduce the worm burden. However, research on alternate grazing with cattle has shown that this method is not very successful (Bairden et al., 1995; Coop et al., 1985). Alternate grazing also carries the risk of nematodirus infection (Coop et al., 1988; Coop et al., 1991; Mitchell et al., 1985). The lower stocking rate required by the organic standards (Defra, 2006) also reduces the worm burden (Thamsborg et al., 1996; Thamsborg et al., 1998). However, on organic farms where helminthiasis is a problem in the lambs some kind of treatment may be needed. Botanical or other alternative dewormers may be useful (Duval, 1994; ADAS, 1996). However, if the use of anthelmintics is inevitable in the case of a heavy worm burden on the farm, the best approach would be to prevent the periparturient egg rise in the ewes. Ewes lambing outside should be dewormed before entering the lambing fields or, if this is too stressful, when leaving the lambing fields, with a product that also kills arrested larvae. Ewes lambing indoors should be wormed at turnout.
The use of the AV class of antheminthics is not acceptable in organic farming, except for moxidectin, because of environmental concerns. Using this method, the worm burden may be reduced substantially and the lambs may not require worming. In the long run, this method, together with the lower stocking rates, may eliminate the need to use anthelmintic wormers. The faecal egg output (see section on faecal egg counts) may have to be checked regularly by faecal sampling. Permission for worming the ewes has to be obtained from the certifying body.
Where nematodirus is a problem, lambs should not be grazed on land grazed by lambs or calves during the previous year. The nematodirus burden changes from year to year. MAFF has developed a forecasting system for the United Kingdom based on soil temperatures in the early spring which can predict the likely severity of nematodiriasis (Smith and Thomas, 1972).
Anthelmintic resistance is a growing problem. A background is provided here and there are further sections under Control and Treatment sections.
One of the main problems in conventional farming concerning helminth infections is the appearance of anthelminthic resistance (Coles, 1997; Coles, 1998; Jackson and Coop, 1999). The development of species and populations of parasitic helminths with resistance to one or more anthelmintics is an increasing problem world-wide (Taylor et al, 2002). The almost exclusive use of anthelmintic treatment in conventional livestock farming has resulted in development of anthelmintic resistance (Fontenot et al., 2003).
Three characteristics of breeding management can be identified in the build up of anthelmintic resistance:
(1) the introduction of resistant worms through the purchased animals or common pastures grazed by several flocks,
(2) under-dosing and the repeated use of one class of drugs, and
(3) the size of the population of infective larvae on pastures at the time of the treatment.
The selection processes for anthelmintic resistance may occur at an early stage of development within the parasites. This may have severe implications for the early detection of anthelmintic resistance (Bartley et al., 2005). The most efficient way to limit the increase of anthelmintic resistance is the reduction of the selection pressure by drugs, and optimal timing to maximise their efficacy (Slivestre et al., 2002).
The majority of currently available anthelmintics belong to three main groups, the benzimidazoles, imidazothiazoles and the avermectins/milbemycins. A variety of in vivo and in vitro tests have been developed for the detection of nematode populations resistant to the main anthelmintic groups, but each suffers to some degree from reliability, reproducibility, sensitivity and ease of interpretation (Taylor et al., 2002). The faecal egg count reduction (FECR) in faeces is the most widely used method to assess the efficacy of these anthelmintics against gastrointestinal strongyles. It 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) propose using individual animal FECR tests that give equal weight to every tested host. Individual FECR provide reliable evaluation when egg counts are over 300 eggs/g and when at least 10 animals were tested (See also Treatment section).
Coles et al., (2005) demonstrate the ease with which ivermectin resistance in H.contortus can be selected if high selection pressure is applied.
Knowledge of the roundworm life cycle and infection patterns makes it possible to identify 'risk periods', and not grazing a field during the 'risk period' minimizes the risk of infection. Two terms are generally used with regard to clean grazing: clean pastures and safe pastures.
A clean pasture is one free from infection, in the sense that it will not turn susceptible animals grazing it into a significant source of contamination (Cawthorne, 1986). Clean pastures are therefore either:
Pastures that have not been infected at all; e.g. newly established grass leys following an arable crop.
Pastures where the infection has died out and is no longer active; e.g.
Pastures that have not carried sheep in the previous twelve months;
From July onwards - aftermaths that have been free of sheep since the previous autumn;
From July onwards - grazings that have carried cattle since the previous spring and have been free of sheep since the previous autumn
A safe pasture is one on which the level of infestation is unlikely to affect the performance of animals grazing on it, though they may become a source of contamination (Cawthorne, 1986). In conventional farming, this usually means pastures which have been grazed previously by sheep dosed with anthelmintics. Pastures grazed by cattle since the previous July may also provide safe grazing, but there may be a risk of Nematodirus infection.
Systems of clean grazing have been described in MAFF (1981). See also MAFF (1980).
On lowland farms there is usually a plentiful supply of alternate grazing, rotation of grass and crops are often a feature and therefore new leys and aftermaths are available each year. Although many conventional lowland farmers use anthelmintics regularly in both ewes and lambs, good control can be achieved with clean grazing only. The lower stocking densities in organic farming also reduce the worm burden of the lambs (Thamsborg et al., 1996).
Annual climatic fluctuations and seasonal variations in the development of species of gastrointestinal nematodes may limit the sole use of evasive grazing to a small proportion of farms (mixed dairy cattle/sheep farms; some organic dairy goat farms). However, there are possibilities to combine evasive grazing with other methods in an integrated control scheme (Eysker et al., 2005b).
Nematode larvae populations have been shown to differ between herbage species, potentially due to differences in crop morphology or microclimate beneath the sward (which may affect larval development and survival, or the number of coprophagous or nematophagous organisms at soil level) (ADAS, 2004).
Vegetation type and stocking density potentially may be manipulated to regulate rates of faecal breakdown as part of an integrated parasite control strategy to be developed against intestinal parasites of sheep. This is associated with the number of invertebrates present in different grass leys (Williams and Warren, 2004).
Extensive research has been conducted in the area of breeding for helminth resistance (Bishop et al., 1996; Bisset et al., 1997; Douch et al., 1996; Hohenhouse et al., 1998; McEwan et al., 1997; Morris et al., 1997; Satyavir Singh et al., 1998; Stear et al., 1997; Stear et al., 1998; Woolaston et al., 1997).
Selection for resistant sheep is possible with a limited risk of adaptation of the nematode parasites, although Saulai et al (2001) stress that long-term monitoring of nematode adaptation should be scheduled if host selection is planned. Compared with experimental vaccination and protein supplementation, genetic selection for resistance to Haemonchus contortus, showed the largest and most persistent effect on faecal egg count in the host, and worm contamination on pasture (Eady et al., 2003).
Breeds of sheep with resistance to nematode infection often display a reduced periparturient rise (PPR) in faecal egg counts (FEC) when compared with susceptible sheep. (Courtney et al., 1984; Courtney et al., 1985; Zajac et al., 1988, Rocha et al, 2004).
A number of novel findings arose from Defra project “Genetic control of resistance to gastro-intestinal parasites in hill sheep (Project LS2204) (Roslin Institute, 2000) including:
· The peri-parturient rise is a heritable phenomonen, and thus can be genetically changed;
· Increasing the reproductive burden on ewes will worsen the periparturient rise;
· There is a genetic trade-off between resources the ewe puts into fighting periparturient nematode infections and the resources put into nurturing the lamb;
· Resistance to Nematodirus infections in the lamb is heritable and not subject to maternal influence; and
· In lambs, resistance to Nematodirus is positively correlated with resistance to Strongyles and thus can be used as a predictor of Strongyles resistance in the absence of Strongyles challenge.
The heritability estimate for natural resistance to H.contortus varies considerably between breeds (Gauly et al., 2002) and it has been suggested for some breeds that the breeding decisions can be based on one or two samples depending on the mean values and ranges of FEC and haematocrit (the ratio of the volume occupied by packed red blood cells to the volume of whole blood) readings (Gauly et al, 2001).
There may be both favourable and unfavourable relationships between production traits and improved resistance to gastro-intestinal parasites. Resistant sheep have been shown to grow more wool without parasite infection and to respond in terms of changes in feed intake, weight change and wool growth (Lui et al, 2005).
Texel sheep are more resistant to natural nematode challenge than Suffolk sheep based on FEC and nematode burden (Good et al, 2006). Notter et al (2003) suggest that Caribbean hair breeds may be able to contribute significantly to development of parasite-resistant sheep populations. In Poland, Nowosad et al., (2003) showed a significant breed effect on resistance to nematode infection. Polish long-wool ewes excreted three times fewer eggs than Blackface ewes and possessed 1.5 fewer nematode eggs in their faeces than the Weisses Alpenschaf breed.
The genetic mechanisms in sheep which are responsible for resistance to other strongyle nematodes probably also influence resistance to Nematodirus infection (Morris et al, 2004). Comparisons of Teladorsagia circumcincta and Trichostrongylus colubriformis populations in sheep with differing resistance status indicated that the number, size and fecundity of the worms may well be regulated by similar mechanisms in both species, but T colubriformis seemed to be more intensively regulated than T. circumcincta. Worm length is closely associated with the resistance status of the host (Gruner et al, 2004a).
Since selection for resistance to nematode parasites in lambs is possible this factor could be incorporated as part of an overall index for productivity (Roslin Institute, 2000), which, in turn, could result in improvements in productivity over and above those possible for selection for performance alone. In the absence of an appropriate Strongyles challenge, Nematodirus egg counts can be used as a genetic predictor (Roslin Institute, 2000). Selection will also reduce pasture parasite contamination. Since some aspects of host resistance to gastrointestinal parasites are under strong genetic control, these quantitative trait loci could be utilised in a marker-assisted selection scheme to increase host resistance (Davies et al., 2006).
Selection for improved maternal performance (increased prolificacy or increased lamb weight gain) will worsen the peri-parturient rise and increase pasture larval contamination. Selection for improved maternal performance must either be
a) coupled with improved management techniques to avoid such contamination reaching the lamb or
b) coupled with selection aiming to minimise increases in the periparturient rise (Roslin Institute, 2000).
Eosinophil granulocytes, commonly referred to as eosinophils (or less commonly as acidophils), are white blood cells that are responsible for combating infection by parasites in the body. Eosinophilia is a well documented feature of helminth infections but the precise nature of the interaction between parasite and eosinophil remains unclear. It has been hypothesised that sheep nematodes actively encourage eosinophils and that nematode chemo-attractants could offer future potential as novel therapeutic targets (Wildblood et al., 2005). Under defined circumstances, eosinophil concentrations may be a useful indicator of resistance to predominantly, T. circumcincta infection (Stear et al., 2002).
The mechanisms of immunity to Haemonchus contortus infection are discussed by Balic et al (2002).
Importance of diet
The influence of diet on resistance and resilience to helminth infections has been studied (Houtert et al., 1996; Wallace et al., 1998) and the scientific evidence to support the role of nutrition in the control of internal parasites is strong, and entirely consistent with organic standards (ADAS, 2004).
Subclinical infection of sheep with gastrointestinal nematodes results in the diversion of nutrients from growth and development towards the repair of damaged intestinal tissues and to sustain the metabolic shifts (nutritional, hormonal and immune) occurring in tissues affected by the parasites (Roy et al., 2003). Nutritional status of the host can influence the pathogenesis of parasitic infection and well-nourished animals generally withstand parasitism better than those less adequately fed. These metabolic effects, which include decreased nitrogen retention and increased amino acid utilisation are described by Roy et al.,(2003.)
Protein supplementation has been found to lower the periparturient egg rise (Donaldson et al., 1997). The periparturient relaxation in immunity (PPRI) where a short-lived increase in faecal egg counts is observed during late pregnancy and lactation is exacerbated during protein under-nutrition (Huntley et al, 2004).
Intake seems to be the primary determinant of the expression of immunity in sheep selected for resistance against nematodes, with ad libitum fed animals producing more effective defence. Enhanced immune response of lambs consuming high levels of energy and adequate levels of protein have been shown compared to a restricted diet (Valderrabano et al., 2002).Nutritional regimes that minimise the impact of worm infections and enhance the immune response require investigation and integration into sustainable control practices (Besier and Love, 2003).
In lambs infected with Haemonchus contortus, supplementary protein improves both development of immunity and resilience in breeds of sheep that are susceptible to haemonchosis, but in relatively resistant breeds dietary supplementation appears unnecessary (Steel, 2003). Response to protein supplementation of lambs infected with Trichostrongylus colubriformis depends on the metabolisable protein content of the basal diet and on the period of exposure to incoming larvae. Where the diet only meets requirements for maintenance or low growth rates, increased supply of rumen undegradable protein enhances immune expression in terms of reducing faecal egg count and expelling adult worms, but does not appear to limit the initial establishment of incoming larvae. Effects on growth rate and wool production are most pronounced during the period of worm expulsion, indicating that this phase of the immune response competes with production when nutrient resources, and particularly protein, are limited (Steel, 2003).
Maternal body reserves are less critical to the loss of host immunity during early lactation than current nutritional status. Conversely, good nutrition in early lactation can at least to some degree ameliorate the potential impact of reduced body condition on faecal egg output (ADAS, 2004).
Infection in young resistant sheep may require additional requirements of both daily metabolisable energy and metabolisable crude protein whereas at an older age (18 months), the additional nutrient requirement is no longer evident (Liu et al., 2005). It has been suggested that an improvement of nutrition, and in particular the sulphur-containing amino acids, is required to recover the loss of productive performance caused by infection (Liu et al, 2005).
The use of condensed tannin-containing herbage shows promise as a means of lowering faecal egg counts. Niezen et al., 1998a raises the question as to whether the positive effect of tannin-containing herbage on faecal egg counts is due to an anthelminthic effect of the tannin itself or to an improved protein supply to the small intestine.
An effect of herbage species has been found on the population dynamics and vertical migration of Trichostrongylus colubriformis and T. circumcincta larvae (Niezen et al., 1998b). This finding is especially relevant to organic farming as ruminant production is based on roughage feeding and on a more diverse use of herbage species.
Condensed tannins can have either beneficial or detrimental effects on ruminants, depending on the concentration in which they are fed. The condensed tannin concentration in plants tends to be higher in leaves than in stems. In some species the concentration of condensed tannins in leaves can double during the growing season e.g. Onobrychis and Lotus, but in others it remains stable e.g. Cichorium. Reductions in total amount of condensed tannins due to the declining proportion of leaves is balanced by the increasing concentration of in leaves resulting in almost constant concentrations during the season (Haring et al., 2005).
Dietary quebracho tannin may reduce nematode worm burdens through a toxic effect that requires direct contact between parasite and tannin (Butter et al., 2001). This raises the possibility that feeding locally available plant material containing condensed tannins may be an alternative method for controlling parasite infections. Variations in the effects of tanniferous plants on the control of gastrointestinal nematodes depends on factors related to plants or parasites with tannins being partly responsible for the effects (Paolini et al., 2004). However, a major limitation of many novel crops is their tendency for poor establishment and persistency, and it is difficult to see how the specific use of these crops for parasite control could be widely recommended to UK organic farmers at the present time (ADAS, 2004).
Chicory and the condensed tannin-containing legumes Lotus comiculatus L. (Birdsfoot Trefoil) and sulla (Hedysarum coronarium) are viewed as offering the most advantages. Compared with chicory and Lotus; perennial ryegrass and Lotus; perennial ryegrass and white clover, a chicory sward alone showed the greatest potential in terms of agronomic performance, improved trace element status, and ability to reduce FEC in lambs (ADAS, 2004). Chicory and sulla promoted faster growth rates in young sheep and deer in the presence of internal parasites as well as showing reduced methane production. Lotus was not as effective as chicory and sulla in promoting growth of lambs in the presence of internal parasites.
Grazing on Lotus has been associated with increases in reproductive rate in sheep, increases in milk production in both ewes and dairy cows and reduced methane production, effects that were mainly due to its content of condensed tannins. Grazing ewes on Lotus during mating and very early pregnancy may also reduce lamb mortality (Ramirez-Restrepo and Barry, 2005).
The effectiveness of grazing Lotus in achieving increased growth rates and reduced reliance on anthelmintics have been associated with increased metabolisable protein supply, the protein binding action of condensed tannins and the ability of the plant to maintain high metabolisable energy during dry conditions (Ramirez-Restrepo et al, 2005). Supplementation with condensed tannins conferred advantages on the performance of parasitised sheep on a high- but not on a low-protein food (Athanasiadou et al., 2001).
Onobrychis viciifolia (sainfoin), has a consistently high concentration of condensed tannins (CT) throughout the whole growing season. The optimal time for harvest can be determined in relation to agronomic properties such as fodder quality and yield and does not have to be related to a specific time period with high tannin concentration in the herbage. Despite its high condensed tannin content, animals accept sainfoin very well. The anti-parasitic properties of fresh sainfoin are largely preserved in silage and hay (Lüscher et al., 2005).
Beneficial anti-parasitic properties of tannin-rich plants have also been demonstrated by others including Thamsborg et al. (2001), Thamsborg et al. (2003), Niezen et al. (2002), Deane et al. (2002), Marley et al. (2003), Paolini et al. (2005), Hoste et al. (2005), Ramirez-Restrepo et al. (2005) and Barrau et al. (2005).
Conflicting results were obtained for chicory in MAFF project OF0147 (ADAS, 2001), which showed reduced faecal egg output in two years out of three. It was suggested that chicory may reduce parasite load by limiting the migration of larvae above 5cm on the plant, or by improving copper status in the lambs.
Thamsborg et al (2001) identified a number of problems to be addressed with regard to the use of tannin-rich species:
1. Species better suited locally should be found. Sainfoin is not competitive in leys, and weeds dominate, particularly in organic farming without herbicidal use. Sulla, which is a Mediterranean plant, does not overwinter.
2. The efficacy is relatively low. Knowledge of the mechanism of action may indicate ways of improving the efficacy. Selection of appropriate cultivars or growing conditions is needed.
3. The activity in cattle and goats needs to be investigated.
4. The forages need to be integrated in other systems of control, most likely repeated moves or biological control. The implementation is governed by the seasonality of the forages and the epidemiology of the infections.
The potential of the nematophagus fungi Duddingtonia flagrans in the control of nematode parasites has been investigated (Dick, 1996; Faedo et al., 1998; Githigia et al., 1997; Larsen et al., 1998). More research is required, especially in the area of application.
The fungus Duddingtonia flagrans has a capacity to prolifically produce high numbers of thick-walled resting spores, chlamydospores which survive passage through the gastro-intestinal tract of grazing livestock and are capable of growing and subsequently trap nematodes, including larval stages of parasitic nematodes. The nematode-trapping fungus has potential to be used to control three species of gastro-intestinal nematodes: Haemonchus contortus, Ostertagia (Teladorsagia) circumcincta or Trichostrongylus colubriformis in both goats and sheep (Waghorn et al., 2003; Flores-Crespo., 2003; Chartier and Pors, 2003; Paraud and Chartier, 2003; Bogus et al, 2005; Fontenot et al., 2003).
The combination of the nematode-trapping fungi Arthrobotrys musiformis and Duddingtonia flagrans has been shown to be effective in capturing larvae of Haemonchus contortus with no antagonistic effect (Chauhan et al. 2005). In the southern hemisphere, the nematophagous fungi Monacrosporium gephyropagum, A. cladodes, A. conoides and A. oligospora reduced the number of third-stage larvae of the parasite Trichostrongylus colubriformis (Hay et al., 2002). M. haptotylum and H. bysmatosporum were ineffective.
D. flagrans is ineffective against the small lungworm Muellerius capillaris first-stage larvae and cannot be considered as a non-chemotherapeutic approach to the control of the small lungworm in goats (Paraud et al, 2005).
Practical delivery systems such as slow release devices, feed-blocks, etc are required if this is to be a practical tool in future integrated control strategies alongside other strategies such as grazing management, limited use of existing drugs, parasite resistant breeds, bioactive forages, and possibly vaccines (Hertzberg et al., 2002).
Although Knox et al., (2002) showed no detectable negative environmental impacts of D. flagrans use in a typical improved pasture, Faedo et al (2002) concluded that the application of D. flagrans as a biological control agent against the free-living stages of nematode parasites of these livestock will negatively affect populations of non-target soil nematodes. Daily spore feeding of goats with may provide more consistent larval reduction than less frequent feeding (every second or third day) (Terrill, 2004).
Unusually warm and dry summer conditions can effect the epidemiology of parasitic gastroenteritis and can have reduce the effectiveness of D. flagrans as a method of control. The consequence for the application of evasive grazing as a control option in that suppression of adult burdens might still be necessary, through a limited use of anthelmintics or through alternative deworming strategies (Eysker et al., 2005a).
Antihelminthic drugs may have anti-fungal activities although the inhibition of the full predatory activity of D. flagrans in faeces following treatment with benzimidazole is only short lived (Paraud et al., 2004). The potential of A. musiformis as a control is enhanced by its ability to survive passage unprotected through the gastrointestinal tract (Graminha et al., 2005).
Faecal Egg Counts
Faecal worm egg counts, pasture larval numbers, the presence or absence of scouring lambs and lamb growth rates are all potential indicators of parasitic gastro-entiritus (PGE) status (Gray 2002). Faecal Egg Counting (FEC) is a simple diagnostic technique, which calculates the number of internal parasite eggs per gram (EPG) of faeces. Composite faecal egg counts are increasingly used to support strategic anthelmintic treatment decisions in grazing livestock (Morgan et al., 2005). They give a reasonable estimate of worm burdens in young ruminants, especially lambs (McKenna, 1981 and McCoy et al., 2005). The accuracy is affected by the number of individual samples included, how thoroughly they are mixed, and the underlying degree of parasite aggregation between individual hosts.
Faecal worm egg counts are highly variable, being influenced by between and within breed variation, species of parasite, nutrition and level of immunity, so unless they are put into context, the interpretation of faecal worm egg counts can be difficult (Gray, 2002). Other factors, including the age of the animal, grazing history,current performance and growth rates, clinical signs, previous treatments, the time since the last treatment, withholding times and the presence of intercurrent disease need to be considered along with FECs before a decision on when to treat with anthelimintic (McCoy et al., 2005).
A parasite control system, Fecpak International Ltd., New Zealand, incorporating on-farm FECs has been recently introduced to the UK and Ireland. The Fecpak system allows on-farm and rapid assessment of faecal egg counts. The Fecpak unit is a customised purpose-built product containing all the equipment needed for calculating quick and accurate FEC enabling high frequency monitoring.
It can be used to:
• Monitor the trends and level of parasitism in sheep
• Ensure good timing of anthelmintic treatment
• Monitor the effectiveness of specific anthelmintic treatments
• Build worm burden profiles during problem times of the year and also identify fields where heavy worm contamination has occurred
• Monitor the effectiveness of grazing management and other management decisions
An evaluation of using FECPAK to monitor roundworm egg counts in livestock faecal samples is provided by the University of Aberdeen at http://www.abdn.ac.uk/organic/organic_15e.php.
McCoy et al., 2005 suggest that the on-farm Fecpak system is an accurate and reliable means of performing FECs in the hands of skilled, experienced operators. However, flock owners who had received training found it difficult to obtain an accurate worm egg count using the on-farm faecal egg counting kit and, therefore, there are potential risks associated with on-farm diagnosis. There is a risk of over-estimation of worm burden if parasite species identification is not accurate. Whilst McCoy et al. (2005) showed no difference between trained farmer and laboratory Nematodirus egg counts, there was a difference in strongyle worm egg counts counts as a consequence of the wrong identification of stongyloides and strongyle infections. Nematodirus eggs present in the faeces are relatively large and easily recognised. Strongyle infections cause problems in lambs throughout the summer and autumn and the eggs in faeces are relatively small. Strongyloides produce eggs similar in size to strongyle eggs but are generally of little pathogenic importance. Other structures present, such as pollen and coccidial oocysts may also have contributed to the over-estimation of FECs.
See section on Good Practice for advice on the use and interpretation of faecal egg counting.
See section on Treatment for the use of faecal egg counting to monitor anthelmintic resistance.
The FAMACHA(R) Eye-colour-chart
The FAMACHA(R) Eye-colour-chart is based on the principle knowledge that the colour of mucous membranes are correlated with the anaemia situation of an animal. Anaemic animals are identified and classified using a 1 to 5-color scale based on the colour of the conjunctiva, and anaemic animals can be selectively treated. However, studies under low parasite pressure have shown only a low correlation with Haemonchus contortus infection in lambs (Gauly et al., 2004). Kaplan et al (2004) indicate that the FAMACHA(C) method is an extremely useful tool for identifying anaemic sheep and goats in the southern US and US Virgin Islands. They recommend further studies to determine optimal strategies for incorporating FAMACHA(C)-based selective treatment protocols into integrated nematode control programs.