Distribution and repeatability of nematode faecal egg counts in dairy goats: a farm survey and implications for worm control

Gastrointestinal nematode infections in goats: differences between strongyle faecal egg counts and specific antibody responses to Teladorsagia circumcincta in Nera di Verzasca and Alpine goats

Strongylida are gastrointestinal nematodes (GIN) of greatest importance in small ruminants throughout the world. Differences in resistance and resilience to GIN among goat breeds were reported. This study aims to investigate the mechanism underlying the breed-associated differences using a cosmopolitan (Alpine, AB) and an autochthonous (Nera di Verzasca, NV) goat breed. At first, fifteen goats from the same herd (NV = 7, AB = 8) at day 0 were infected with infective larvae (L3) of mixed GIN. From the 15th day post-infection (DPI), individual parasite egg excretion (faecal egg counts, FEC) was performed on all goats, once per week, until the 63rd DPI. Afterwards, in goats under field conditions (30 AB and 30 NV reared on the same farm), individual faecal and blood samples were collected; FEC-specific antibody and PCV levels were explored. In goats with experimental GIN infection, mean eggs per gram of faeces (EPG) values were consistently lower in NV goats. In goats with natural GIN infection, EPG and prevalence values showed high variability in both breeds; among individual variables, breed had a significant influence on EPG. Further, PCV and anti-T. circumcincta IgA levels were influenced by the breed. Lower PCV values were also associated with higher strongyle EPG in AB goats, and anti-T. circumcincta IgA levels were influenced by both strongyle EPG and breed, with IgA levels being higher in AB vs. NV goats and positively associated with EPG. Neither EPG nor breed had any influence on IgE levels. Both studies on experimental and natural infection confirmed that goats of NV are more resistant to infection with gastrointestinal nematodes.

Seasonality of helminth infection in wild red deer varies between individuals and between parasite taxa

Parasitism in wild mammals can vary according to myriad intrinsic and extrinsic factors, many of which vary seasonally. However, seasonal variation in parasitism is rarely studied using repeated samples from known individuals. Here we used a wild population of individually recognized red deer (Cervus elaphus) on the Isle of Rum to quantify seasonality and intrinsic factors affecting gastrointestinal helminth parasitism over the course of a year. We collected 1020 non-invasive faecal samples from 328 known individuals which we then analysed for propagules of three helminth taxa: strongyle nematodes, the common liver fluke Fasciola hepatica and the tissue nematode Elaphostrongylus cervi. Zero-inflated Poisson models were used to investigate how season, age and sex were associated with parasite prevalence and count intensity, while Poisson models were used to quantify individual repeatability within and between sampling seasons. Parasite intensity and prevalence varied according to all investigated factors, with opposing seasonality, age profiles and sex biases between parasite taxa. Repeatability was moderate, decreased between seasons and varied between parasites; both F. hepatica and E. cervi showed significant between-season repeatability, while strongyle nematode counts were only repeatable within-season and showed no repeatability within individuals across the year.

The genetic basis for the selection of dairy goats with enhanced resistance to gastrointestinal nematodes

Gastrointestinal nematodes (GIN) severely affect small ruminant production worldwide. Increasing problems of anthelmintic resistance have given strong impetus to the search for alternative strategies to control GIN. Selection of animals with an enhanced resistance to GIN has been shown to be successful in sheep. In goats, the corresponding information is comparatively poor. Therefore, the present study was designed to provide reliable data on heritabilities of and genetic correlations between phenotypic traits linked to GIN and milk yield in two major dairy goat breeds (Alpine and Saanen). In all, 20 herds totalling 1303 goats were enrolled in the study. All herds had (i) a history of gastrointestinal nematode infection, (ii) uniform GIN exposure on pasture and (iii) regular milk recordings. For all goats, individual recordings of faecal egg counts (FEC), FAMACHA© eye score, packed cell volume (PCV) and milk yield were performed twice a year with an anthelmintic treatment in between. The collected phenotypic data were multivariately modelled using animal as a random effect with its covariance structure inferred from the pedigree, enabling estimation of the heritabilities of the respective traits and the genetic correlation between them. The heritabilities of FEC, FAMACHA© and PCV were 0.07, 0.22 and 0.22, respectively. The genetic correlation between FEC and FAMACHA© was close to zero and -0.41 between FEC and PCV. The phenotypic correlation between FEC and milk yield was close to zero, whereas the genetic correlation was 0.49. Our data suggest low heritability of FEC in Saanen and Alpine goats and an unfavourable genetic correlation of FEC with milk yield.

Study of gastrointestinal parasites in water buffalo (Bubalus bubalis) reared under Mexican humid tropical conditions

The objective was to determine the frequency of gastrointestinal parasites (GP) genera affecting water buffalo (Bubalus bubalis) reared under humid tropical conditions of Mexico. Three hundred eighty-three Munrah breed water buffalo were included, 251 adult females and 132 calves. Feces were directly collected form the rectum of the animals and processed by the McMaster technique. Coprocultures were made to identify the genera of the nematodes. The frequency of GP in B. bubalis was 42%, independently of their age, 60% of calves resulted parasitized. Age had a strong association with the presence of GP (Xi² = 77.4014, d.f. = 1, p = 0.001). The family Trichostrongylidae was found in both age groups. The genera identified were Strongyloides sp. (47.2%), Cooperia sp. (33.9%), and Haemonchus sp. (10.4%), as well as Eimeria sp., Moniezia sp., Trichuris sp., and Strongyloides sp. The highest parasite burden corresponded to the genus Strongyloides sp. with 1108.9 EPG. There is a need to carry out further studies in order to know the prevalence and incidence of nematode affecting to B. bubalis as an introduced animal species to Mexican tropics.

Sheep gastrointestinal helminthiasis in the Sertão region of Paraíba State, Northeastern Brazil: prevalence and risk factors

In this study, we aimed to establish the prevalence and risk factors relating to gastrointestinal helminthiasis, and to characterize the sanitary management practiced among sheep herds in the Sertão region of the state of Paraíba, northeastern Brazil, based on factors that condition the ways of controlling these parasites in these herds. The research was carried out between April and July 2012. We visited 54 farms, where fecal and blood samples were individually collected from 465 animals. On each farm, a questionnaire was applied to gather information on variables relating to potential risk factors. The prevalence of sheep gastrointestinal helminthiasis in the region was 75.9%. At least one animal tested positive for this helminthiasis on 53 (98.1%) of the 54 farms evaluated. The eggs per gram of feces (EPG) analysis showed the following infection burdens: 51.8% with mild infection, 27.1% moderate infection, 9.9% heavy infection and 11.2% fatal infection. Among the sheep farms visited, anthelmintics were used on 81.5% (p <0.05). The most relevant risk factor in this study was the farm area, because it defines the area available for grazing animals. Properties with many animals and little pasture area, which are the most abundant type in the Sertão region of Paraíba, tend to have high prevalence of gastrointestinal helminthiasis, because the animals are more prone to reinfection. The Sertão region of Paraíba presents high prevalence of gastrointestinal helminthiasis among sheep, and the farm area is the most relevant risk factor for the development of these parasites.

Quantifying the sources of variability in equine faecal egg counts: implications for improving the utility of the method

The faecal egg count (FEC) is the most widely used means of quantifying the nematode burden of horses, and is frequently used in clinical practice to inform treatment and prevention. The statistical process underlying the FEC is complex, comprising a Poisson counting error process for each sample, compounded with an underlying continuous distribution of means between samples. Being able to quantify the sources of variability contributing to this distribution of means is a necessary step towards providing estimates of statistical power for future FEC and FECRT studies, and may help to improve the usefulness of the FEC technique by identifying and minimising unwanted sources of variability. Obtaining such estimates require a hierarchical statistical model coupled with repeated FEC observations from a single animal over a short period of time. Here, we use this approach to provide the first comparative estimate of multiple sources of within-horse FEC variability. The results demonstrate that a substantial proportion of the observed variation in FEC between horses occurs as a result of variation in FEC within an animal, with the major sources being aggregation of eggs within faeces and variation in egg concentration between faecal piles. The McMaster procedure itself is associated with a comparatively small coefficient of variation, and is therefore highly repeatable when a sufficiently large number of eggs are observed to reduce the error associated with the counting process. We conclude that the variation between samples taken from the same animal is substantial, but can be reduced through the use of larger homogenised faecal samples. Estimates are provided for the coefficient of variation (cv) associated with each within animal source of variability in observed FEC, allowing the usefulness of individual FEC to be quantified, and providing a basis for future FEC and FECRT studies.

Targeted flock/herd and individual ruminant treatment approaches

In Europe, most nematodoses are subclinical involving morbid rather than mortal effects and control is largely achieved using anthelmintics. In cattle, the genera most associated with sub-optimal performance are Ostertagia and Cooperia whereas in sheep and goats, subclinical losses are most often caused by Teladorsagia and Trichostrongylus. In some regions, at certain times, other species such as Nematodirus and Haemonchus also cause disease in sheep and goats. Unfortunately, anthelmintic resistance has now become an issue for European small ruminant producers. One of the key aims of the EU-funded PARASOL project was to identify low input and sustainable approaches to control nematode parasites in ruminants using refugia-based strategies. Two approaches to optimise anthelmintic treatments in sheep and cattle were studied; targeted treatments (TT) - whole-group treatments optimised on the basis of a marker of infection e.g. faecal egg count (FEC), and targeted selected treatment (TST) - treatments given to identified individuals to provide epidemiological and/or production benefits. A number of indicators for TT and TST were assessed to define parasitological and production-system specific indicators for treatment that best suited the regions where the PARASOL studies were conducted. These included liveweight gain, production efficiency, FEC, body condition score and diarrhoea score in small ruminants, and pepsinogen levels and Ostertagia bulk milk tank ELISA in cattle. The PARASOL studies confirmed the value of monitoring FEC as a means of targeting whole-flock treatments in small ruminants. In cattle, bulk milk tank ELISA and serum pepsinogen assays could be used retrospectively to determine the levels of exposure and hence, in the next season to optimise anthelmintic usage. TST approaches in sheep and goats examined production efficiency and liveweight gain as indicators for treatment and confirmed the value of this approach in maintaining performance and anthelmintic susceptibility in the predominant gastrointestinal nematodes. There is good evidence that the TST approach selected less heavily for the development of resistance in comparison to routine monthly treatments. Further research is required to optimise markers for TT and TST but it is also crucial to encourage producers/advisors to adapt these refugia-based strategies to maintain drug susceptible parasites in order to provide sustainable control.

Goat-nematode interactions: think differently

Goats (caprine) and sheep (ovine) are infected with the same principal gastrointestinal nematode (GIN) species, which provoke similar pathological changes and economic consequences. However, until now, the majority of data on host-parasite interactions have been accumulated from ovine studies. This article aims to emphasize the need for specific caprine studies. It is hypothesized that, owing to divergent evolutionary processes, sheep and goats have developed two different strategies to regulate GIN infections, respectively, based on immune response versus feeding behavior. Generation of additional comparative data should result in a better understanding of the possible trade-offs between these two basic regulatory processes. Goat studies should also help to avoid past errors in the control of GIN species owing to the lack of relevant information.

The role of targeted selective treatments in the development of refugia-based approaches to the control of gastrointestinal nematodes of small ruminants

Anthelmintic resistance is recognised as a major problem affecting small ruminant production worldwide and now threatens the sustainability of many of these systems. One method that has been proposed to prolong the efficacy of our current anthelmintics is the maintenance of a parasite population in refugia (unexposed to a drug) which will maintain the genes for susceptibility within the parasite population. Management strategies that employ refugia-based methods include targeted or strategically timed whole flock treatments, targeted selective treatments (TST), whereby only a proportion of the flock is treated at any one time, and the dilution of resistant with susceptible parasites. The ability to effectively target anthelmintic use relies on the identification of those animals that will most benefit from treatment. This review explains the concept of refugia, describes the role of refugia-based approaches to the management of anthelmintic resistance and reviews the markers that have been studied as indicators for TSTs as well as the implementation of refugia-based strategies. Recent results suggest that targeting anthelmintic treatment on the basis of anaemia, milk production and liveweight gain may offer a means of reducing anthelmintic usage whilst still maintaining animal performance.

The use of targeted selective treatments against gastrointestinal nematodes in milking sheep and goats in Greece based on parasitological and performance criteria

This study compared the use of targeted selective treatment (TST) with systematic whole-flock treatments in 38 dairy sheep and goat farms in Greece. Criteria for individual treatments were either parasitological (nematode faecal egg count) or performance-based (body condition score or milk yield). The possible effect of treatment on resistance to benzimidazole anthelmintics was assessed using the Egg Hatch Test. Mean faecal egg counts decreased during the 12-month experimental period in all groups, and were lowest in the TST group treated according to faecal egg count (P<0.05). The number of sheep and goats treated by TST was reduced compared with systematic treatments. Mean thiabendazole-egg death dose(50) (TBZ-ED(50)) values from all groups were similar at the beginning and end of the study (P>0.05), but significant variation in TBZ-ED(50) was noted over the study period in systematically treated goats (P=0.045). Third stage larvae belonging to the genera Teladorsagia, Trichostrongylus and Haemonchus were dominant throughout the experimental period in all flocks. It was concluded that the use of targeted selective treatment reduced the number of anthelmintic treatments to achieve a similar level of parasite control or animal production and may offer a viable option to combine animal production with effective parasite control in Greece.

Nutrition-parasite interactions in goats: is immunoregulation involved in the control of gastrointestinal nematodes?

Compared to sheep, goats seem to develop a low immune response against the parasitic nematodes of the gastrointestinal tract. Nevertheless, some variability in the host response has been observed either at the individual level or depending on internal (genetic) or external (physiological status, nutrition) factors suggesting the possibility to exploit and manipulate this response. There is good evidence from field studies to suggest that a better plane of nutrition might contribute to improve goat resilience. However, the effects on immunoregulation and host resistance remain less clear. Due to their peculiarities in feeding behaviour ('intermediate browser'), goats represent a valuable model to explore the relationships between the three possible strategies to control nematode infection through nutrition: (i) by increasing the immune response; (ii) by avoiding the infective larvae; and (iii) by selecting plants with direct anthelmintic properties (self medication).

Targeted application of anthelmintics to control trichostrongylosis in dairy goats: result from a 2-year survey in farms

The targeted application of anthelmintic treatments represents one of the current available solutions to slow down the development of anthelmintic resistance within worm populations. Within an experimental flock of dairy goats, control of gastrointestinal parasitism by such selective treatments, targeting the most receptive animals within a flock, was previously found to be effective and to have no detrimental consequences on milk production. The objectives of the current study were to verify the validity of this method in farm conditions. Eleven dairy goat farms from three main areas of production in France were surveyed for 2 years. In six farms, the survey was prolonged for a third year. During year 1, systematic treatments were applied during the grazing season whereas in year 2 and or year 3, treatments were given exclusively to the goats in first lactation and to the multiparous ones with the highest potential of milk production. The level of nematode infection was measured four times per year through individual coproscopical examinations and the mean annual production of milk was recorded. No significant changes in egg excretion nor in milk production were noticed in any farm during years 2 or 3 after switching from the systematic to the selective mode of treatments. These results confirmed that targeted application of anthelmintics might represent a way to combine the control of trichostrongyles and the prevention of anthelmintic resistance.

Comparison of selective and systematic treatments to control nematode infection of the digestive tract in dairy goats

Resistance to anthelmintics in nematode parasite of the digestive tract is a major concern in small ruminants and particularly in goats. One possible solution to limit the development and spread of resistance is to give treatments on a selective basis, i.e. by targeting the most susceptible animals within a flock rather than treating all the animals. In dairy goats, epidemiological studies have shown that, within a flock, goats in first lactation and the multiparous ones with the highest level of milk production were highly receptive to parasite infection. The objective of the study was to assess whether selective treatments could achieve a level of control of nematodes similar to systematic drenching. A similar experimental design was applied for two successive years. An experimental flock of 120 dairy goats was divided into two groups. All the goats from group SYS (systematic treatment) were drenched at mid-grazing season (July). In contrast, anthelmintics in group SEL (selective treatment) were restricted to the goats in first lactation plus the high producers. Overall, these treated goats represented 48% of the flock in year 1 and 66% in year 2. After treatments, both groups grazed on separate pastures. Parasitological and pathophysiological measurements were performed monthly. The results indicate a similar level of egg excretion in the two groups. The pathophysiological parameters (pepsinogen and phosphate concentrations) were also similar in the two groups, as well as the milk production for the 2 years. These results suggest that a targeted use of anthelmintics may allow efficient control of gastrointestinal nematodes whilst resulting in a predicted reduction in the selection pressure for the development of anthelmintic resistance.