Cyathostomins In Horses Research Articles

First report of ivermectin resistance in cyathostomins (small strongyles) of horses in Argentina

In Argentina, as in the rest of the world, cyathostomins are the most common nematodes parasitizing horses. Control is based almost exclusively on the administration of benzimidazoles, pyrimidines, and macrocyclic lactones. However, intensive use of these drugs is resulting in the development of anthelmintic resistance (AR). For example, AR to benzimidazoles is currently distributed throughout Argentina, while incipient AR to pyrimidines (pyrantel embonate) is appearing in areas where this drug is used. Macrocyclic lactones and especially ivermectin, are by far the most used drugs by the vast majority of equine premises in the country. Although ivermectin has been used since 1982, its efficacy against equine strongylid parasites has remained very high until the present. In this study we report for the first time, the presence of a cyathostomin population with resistance to ivermectin in adult horses belonging to an equine premise located in central Argentina. Fecal egg count reduction tests (FECRT) were performed following the most recent guidelines of the World Association for the Advancement of Veterinary Parasitology (WAAVP) for the diagnosis of anthelmintic resistance (research protocol) and resistance was considered when the Upper 90% Credible Interval fell below the expected efficacy threshold of 99.9%. Calculations were carried out using two different online calculation interfaces suggested by WAAVP. For the 14-day post-treatment interval, ivermectin efficacy was 79.5% (90% Credible Interval: 68.1–88.8) and 79.3% (74.2–83.6.3%) with the two methods, respectively. At 19 days post treatment, fecal egg count reductions were 68.6% (50.5–83.1) and 68.4% (61.9–74.1), respectively. At both intervals, this cyathostomin population fullfilled the criteria for AR. These findings suggest dispersion of ivermectin resistant cyathostomins in Argentina. Given the widespread use of macrocyclic lactones, it is important that veterinarians and the equine industry promote a more selective and evidence-based use of these drugs and establish routine monitoring to determine anthelmintic field efficacy to detect treatment failures as early as possible and avoid potential health problems as well as further spread of resistant genes.

Effect of temperature on the development of the free-living stages of horse cyathostomins.

Cyathostomins are considered as the most prevalent and pathogenic parasites of grazing horses. The development on pastures of the free-living stages of these gastrointestinal worms is particularly influenced by outdoor temperature. Understanding the bionomics of free-living stages is an important prerequisite to implement mathematical models designed to assess the parasitic risk for grazing equids. The aim of this study was to assess the effect of 3 constant temperatures under laboratory conditions (10±1°C, 23±2°C, 30±2°C) and one fluctuating temperature under outdoor conditions (mean: 17±4°C) on the minimum time taken by cyathostomin eggs to develop into first/second stage larvae (L1/L2) then into infective third stage larvae (L3) in horse faeces. According to the temperatures, the minimum time taken by eggs to develop into L1/L2 was between 1 and 3days and into L3 between 4 and 22days. At 10°C, the development time of eggs into L3 was the longest and at 30°C the fastest. The results were consistent with historically available data and their compilation should lead to the improvement of parameterised models assessing the parasitic risk period in grazing equids.

Strong Ivermectin Resistance in Cyathostomins of Horses: A Grim Picture for Sustainable Parasite Control

Strong Ivermectin Resistance in Cyathostomins of Horses: A Grim Picture for Sustainable Parasite Control

Cyathostomin faecal egg counts in horse farms from Central Italy.

Cyathostomins, or 'small strongyles', are the most important equine helminths because of their worldwide distribution, spread of anthelmintic‑resistant populations, and pathogenic impact. The so‑called 'selective treatment' of those animals exceeding a certain faecal egg count (FEC) has recently been proposed to implement cyathostomin control programmes. The present study evaluated the extent of egg shedding in 475 horses living in 12 farms from 3 regions of Italy. All examined farms and 224 horses (47.6%) were positive for cyathostomins. 138 horses (28.8%) scored positive for cyathostomin FECs with a range of eggs‑per‑gram of faeces (epg) values of 50‑2,150. Further 86 horses (18.1%) were positive only under qualitative microscopy (i.e. < 50 epg). Of the animals with a FEC > 50 epg, 81 (17%) and 57 (12%) showed values of 50‑200 and > 200 epg, respectively. The findings from this study demonstrated a reduced presence of high‑shedding horses compared to results obtained in previous years in the same study areas, despite overlapping climate features in the previous 5 years. A continuing monitoring of epidemiological and biological features of horse cyathostomin infection is crucial for planning intervention programmes aimed to maintaining animal health and preserving the efficacy of parasiticides.

Procyanidin A2 in the Australian plant Alectryon oleifolius has anthelmintic activity against equine cyathostomins in vitro

There is a need to investigate new methods of controlling cyathostomins in horses due to increasing anthelmintic resistance amongst these parasites. In a previous study we identified the Australian plant Alectryon oleifolius as having anthelmintic activity towards cyathostomins. This study aimed to isolate and identify the bioactive compound(s) responsible for all or part of this anthelmintic activity and quantify its activity in vitro. The condensed tannin procyanidin A2 was isolated from the plant through a process of bioassay guided fractionation and identified using 1D and 2D nuclear magnetic resonance spectroscopy and high performance liquid chromatography with mass spectrometry. Procyanidin A2 demonstrated significant anthelmintic activity in larval development assays, completely inhibiting development from egg to third larval stage at concentrations as low as 50μg/mL and having an IC50 value of 12.6μg/mL. Procyanidin A2 also significantly inhibited larval migration at concentrations of 25μg/mL. This study indicates that procyanidin A2 is the principal anthelmintic compound in extracts from A. oleifolius, and further highlights the potential for the use of this plant as a component of cyathostomin control programs in the future.

In vitro evaluation of ivermectin, moxidectin, albendazole and pyrantel against cyathostomins of horses.

Cyathostomins are the most prevalent nematodes of horses, and multidrug resistance has been reported worldwide. There is a need to implement alternative drug monitoring analytical tests. The objective of this study was to determine the consistency (5 repetitions) of the larval migration on agar test (LMAT) using ivermectin, moxidectin, pyrantel or albendazole against cyathostomin infective-stage larvae in eight different concentrations. LMAT showed a strong coefficient of determination (R2 > 0.91), between the test repetitions (n=5). The average 50% effective concentration (EC50) for ivermectin, moxidectin, pyrantel and albendazole were 0.0404, 0.0558, 0.0864 and 0.0988 nMol, respectively. The results of the EC50 for albendazole showed the greatest range of concentration. Ivermectin and moxidectin had the lowest in between-test variation. In the future, internationally certified susceptible isolates could be used for screening new drug candidates, or to follow up the pattern of drug efficacy from field populations.

Diagnosis of resistance alleles in codon 167 of the beta-tubulin (Cya-tbb-1) gene from third-stage larvae of horse cyathostomins

Anthelmintic resistance is a serious problem for the control of equine gastrointestinal nematodes. In the present survey, 173 third stage larvae of cyathostomins were investigated from three different locations for the presence of the resistant genotype at codon 167 of the beta-tubulin gene, as this is the most prevalent mutation. The larvae from the state of Parana (n=67), Sao Paulo (n=54) and Santa Catarina (n=52), showed 61.2; 31.5 and 38.5% of the heterozygous resistant genotype - TTC/TAC, respectively. An unpublished mutation at codon 172 that results in a serine (S) to threonine (T) substitution was found in 17.9% (12/67) of samples from Parana; and 13.0% (7/54) of samples from Sao Paulo. We have compared the molecular diagnostic with the fecal egg count data (R2=−0.79) from the same farms, and consider that the use of routine molecular diagnostic in individual larva may help to determine the population genetic distribution that is associated with drug failure.

Species composition of larvae cultured after anthelmintic treatment indicates reduced moxidectin susceptibility of immature Cylicocyclus species in horses

For the control of cyathostomins in horses, the macrocyclic lactones (MLs), moxidectin (MOX) and ivermectin (IVM) are the most commonly used anthelmintics. However, reduced activity, observed as shortening of the egg reappearance period (ERP) has been described. Shortening of the ERP may be caused by a decreased susceptibility of immature worms for MLs. Alternatively, immature worms may develop faster into egg producing adults as a result of repeated ML treatments. The species composition of the larval cultures obtained shortly after ML and pyrantel (PYR) treatment can confirm the hypothesis of decreased ML susceptibility, as this is often class-specific, whereas faster development would also occur after treatment with anthelmintics with a different mode of action. From 3 farms with a known history of shortened ERP, 8 horses per farm were selected and divided into 2 groups. The MOX-PYR-MOX group was treated twice with MOX (day 0 and 126) and once with PYR (day 84) and the IVM-PYR-IVM group was treated twice with IVM (day 0 and 98) and once with PYR (day 56). Cultured infective larvae (L3s) were counted and differentiated with the reverse line blot on pooled samples. Per cyathostomin species, the number of larvae per gram was calculated. The efficacy of all ML treatments was 100% and a shortened ERP was found on all 3 farms. The species composition of the larval cultures after ML treatment did not differ significantly from that after PYR treatment in the IVM-PYR-IVM group, but it did differ in the MOX-PYR-MOX group. The larval cultures obtained after MOX treatment consisted mostly of Cylicocyclus nassatus, while after PYR treatment Cylicostephanus longibursatus was the most abundant species. In the cultures from 42days after MOX treatment 6 cyathostomin species from 3 genera were found on the farm with the lowest activity (farm 1), while on the farm with the highest activity (farm 3) only 3 species from one genus were found in the same number of examined L3s. The high numbers of L3s of Cylicocyclus species 42days after MOX treatment and the low numbers 42days after PYR treatment can be explained by reduced susceptibility of the immature worms to MOX, but not by a faster development. In conclusion, shortening of the ERP following MOX treatment is most likely a process in which an increasing number of immature worms from an increasing number of species is becoming less susceptible to the active compound.

The prevalence, abundance and distribution of cyathostomins (small stongyles) in horses from Western Romania

Forty seven working horses from Romania were post-mortem examined for small strongyles (Cyathostominae) infections. All horses were found infected. The overall cyathostomins intensity ranged from 390 to 13,010 and horses were infected by 8–24 species. The intensity was higher in ventral colon (1531) and dorsal colon (824), the lowest in the caecum (524). Twenty four species were identified. Cyathostomum catinatum, Cylicocyclus insigne, and C. Nassatus had 100% of prevalence. Over 50% of horses were infected by Coronocyclus coronatus, Cylicostephanus calicatus, C. goldi, and C. longibursatus. Other prevalent species (34%–45%) were Cyathostomum tetracanthum, Cylicostephanus minutus and Gyalocephalus capitatus. Coronocyclus labiatus, Parapoteriostomum mettami, Poteriostomum imparidentatum and P. ratzii had the lowest prevalence. Most species showed high organ preference with a niche breadth value between 1 and 1.96 while only 7 species (Coronocyclus labiatus, Cyathostomum tetracanthum, C. brevicapsulatus, Cylicocyclus elongatus, C. insigne, C. leptostomum and C. radiatus) showed a more generalist selection. The niche breadth of 10 species was significantly (p<0.05) influenced by itself intensity (Coronocyclus labratus, Cyathostomum pateratum, C. tetracanthum, Cylicocyclus elongatus, C. radiatus, C. ultrajectinus, C. leptostomum, Cylicodontophorus euproctus, Poteriostomum imparidentatum, P. ratzii). The niche breadth of Cylicocyclus nassatus was positively (p<0.05) influenced by the summed intensity of the other species while that of Cylicocyclus elongatus was negatively (p<0.05) influenced by the intensity of the other species. The cluster analysis of the Cyathostominae community composition showed a major cluster composed by the three dominant species, followed by a cluster composed by Coronocyclus coronatus, while all the other species presented a tree like structure.

Morphometric Study of Infective Larvae of Cyathostomins of Horses and Their Distribution

Cyathostomins or small strongyles account for more than 50 species of intestinal parasites of horses, and it becomes a challenge to identify these nematodes even at the genus level. Although the available morphological keys consider the number, shape, and arrangement of the intestinal cells of infective larvae (L3) into: types A, B, C, D, E, F, G, H, Gyalocephalus capitatus, and Posteriostomum spp, there are limited scientific reports. The aim of this study was to identify L3s and to determine their frequency and morphometric features from eight horse-breeding farms from two different breeds. Feces from naturally infected adult animals were collected, and the fecal culture was performed using a pool from each location. Optical microscopy was used to identify (n = 400) which type of L3. Another group of larvae (n = 160) were measured using a macroimaging station microscope. The frequency of L3s for types A, B, C, D, E, F, G, H, and G. capitatus were 62, 1.3, 5.7, 25.3, 1.4, 2.3, 0.4, 1.1, and 0.5%, respectively. Cyathostomins type A was the most common larva, followed by type D. The results indicate that Thoroughbred horses have a more heterogeneous parasitic fauna than the Criollo horses. The average size of the larvae was 734.5 μm (±58.3) for type A, 743.3 μm (±49.7) for type C, and 742.5 μm (±48.7) for type D. This study reinforces the importance of identifying and determining the prevalence of cyathostomin infective stage larvae to complement studies on their biology and epidemiology in horses.

Efficacy of selected anthelmintic drugs against cyathostomins in horses in the federal state of Brandenburg, Germany

Cyathostomins are currently the most common internal parasites of horses. With the intensive use of anthelmintic drugs over the past decades, resistance of cyathostomins to anthelmintics is becoming a growing problem in many countries. The aim of this study was to assess the current situation on horse farms in the German federal state of Brandenburg. A pre-selected population of horses from 24 premises that had shown a prevalence of cyathostomins higher than the average in a previous study was examined for anthelmintic efficacy. Faecal egg count reduction tests (FECRTs) were performed for ivermectin (IVM) and pyrantel (PYR). For IVM, the egg reappearance period (ERP) was also examined, as a shortened ERP can be indicative of developing resistance. The efficacy of IVM on cyathostomins was high: 99.1% of 224 horses had a zero egg count 14days after treatment. No shortening of the ERP was detected. For the data of the FECRT for PYR, three different methods of calculation were employed: (a) the method as recommended by the World Association for the Advancement of Veterinary Parasitology (WAAVP), (b) a bootstrapping method and (c) a Markov chain Monte Carlo method. Two methods of interpretation for these data were used: Resistance was declared (a) when FECR was <90% and the lower 95% confidence interval (LCL) <80% and (b) when additionally the upper 95% confidence level (UCL) was <95%. When applying the first interpretation, resistance against PYR was found on four yards, while, when considering the UCL, all three methods for calculation only detected resistance on one single yard. Twelve species of cyathostomins were detected in larval cultures derived from strongyle egg positive faecal samples collected 14days after treatment with PYR by reverse line blot hybridization (RLB). In order to generate comparable data, it is suggested to establish international standards for the calculation of FECRT data.

Controlling endoparasites on equine stud farms

Resistance to all of the licensed classes of anthelmintics is now widespread and targeted worming strategies are advocated to reduce selection pressure and delay the onset of anthelmintic resistance. Targeted strategies of worm control are relatively straightforward in adult horses but where youngstock are present the situation becomes more complicated. Youngstock are more susceptible to infection and clinical disease and additional parasites have to be considered in control programmes. Despite the additional complexity, targeted worming strategies can be employed on breeding establishments, and indeed should be, as owners of young horses have the most to lose if anthelmintic resistance develops.

Anthelmintic efficacy against cyathostomins in horses in Southern England

Cyathostomins are considered to be the most important group of helminths to affect equids due to their high prevalence, potential pathogenicity and ability to develop anthelmintic resistance. Their control relies almost exclusively on frequent anthelmintic use. Currently, fenbendazole (FBZ), pyrantel embonate (PYR), ivermectin (IVM) and moxidectin (MOX) are licensed for use in horses in the UK. With no new anthelmintics likely to be licensed in the near future, it is essential that investigations into the efficacy of current anthelmintics in different locations are performed to help inform control programmes. Here, efficacy of FBZ, PYR, IVM and MOX in horse populations in the South of England was investigated. Horses with a strongyle faecal egg count (FEC) of ≥50eggs per gram (EPG) were enrolled onto a faecal egg count reduction test (FECRT) study. Efficacy was determined by calculating the percentage reduction in FEC between the group mean at Day 0 and 14 days post-treatment. Efficacy was indicated when a group arithmetic faecal egg count reduction (FECR) of ≥90% was recorded for FBZ and PYR, and ≥95% for IVM and MOX. Between March and December 2012, 404 FECRT were performed on 12 yards examining 101, 110, 93 and 100 equids for FBZ, PYR, IVM, and MOX, respectively. FBZ resistance was identified on all yards (mean FECR range 0–65.8%). On 10 of 12 yards, PYR efficacy was >90% (91.0–99.4%) and on two yards, PYR resistance was suspected (86.8–87.2%). IVM (96.4–100%) and MOX (99.9–100%) were >95% efficacious on all yards. As the prevalence of FBZ resistance was 100%, the future use of this anthelmintic for the control of strongyles should be questioned. PYR should be used strategically to reduce reliance on the macrocyclic lactone class products. Over-dispersion of FEC between horses was observed (average k=0.21) with 80% of the strongyle eggs counted measured in 15% of horses tested, strongly supporting the application of targeted helminth control programmes in this host species.

Monitoring of anthelmintic resistance in small strongyles in the Czech Republic in the years 2006–2009

The aim of the field study performed in 2006 was to investigate the occurrence and distribution of intestinal helminths in horses based on pre-treatment faecal egg counts. In total, 948 horses bred on 37 farms were tested. Thirty six (97.2%) farms tested were positive for cyathostomins; horses in 9 (24.3%), 6 (16.2%) and 1 (2.7%) different herds tested were positive for Parascaris equorum, Anoplocephala perfoliata and Strongyloides westeri, respectively. In 21 herds, 344 horses with values exceeding 100 eggs per gram were included in the trial for the presence of drug resistant cyathostomins by a faecal egg count reduction test. Horses were treated orally with recommended doses of fenbendazole and ivermectin. Resistance to fenbendazole was detected on 20 farms (95.24%) with values of faecal egg count reduction test ranging from 0 to 90%. Ivermectin remained effective in all tested herds with the value of faecal egg count reduction test 96–100%. In autumn 2008, 178 horses on 10 farms were examined. Of these, only seven horses tested were negative for cyathostomins. One farm was tested positively for Anoplocephala perfoliata, and one for Parascaris equorum. In spring 2009, six farms were examined, four of which were the same farms as in 2006. We found a decreased number of eggs per gram in all horses, but an increase in benzimidazole resistance, which was found in 5 farms out of 6 (faecal egg count reduction test 15.2–84.6%). This is the first wide survey in horses from the Czech Republic. Based on this study, we can conclude that benzimidazole resistant cyathostomins in horses are widespread but ivermectin is still fully effective.

Determination of anthelmintic efficacy against equine cyathostomins and Parascaris equorum in France

SummaryThis article reports the results of a faecal egg count reduction test on 4 farms in France, as an integrated part of the routine deworming strategy against horse cyathostomins and Parascaris equorum. Treatment with fenbendazole (FBZ) or ivermectin (IVM) was evaluated in yearlings on Farms 1 and 2 and treatment with pyrantel embonate (PYR) was tested on Farms 3 and 4. Calculation of the arithmetic mean faecal egg count reduction and the 95% confidence intervals (95% CI) around the mean was performed using bootstrap analysis. For equine cyathostomins, resistance to FBZ was found with an arithmetic mean reduction of 48.8% (95% CI: 1.9–69.3%). On Farms 1 and 2, horses with reduced efficacy were identified. PYR was found to be effective against cyathostomins, with an arithmetic mean reduction of 95.3% (95% CI: 84.6–99.8%), as well as IVM (100%). For P. equorum, both FBZ and PYR were effective (100% reduction). The efficacy of IVM, however, was low (45.5%; 95% CI: 0–96.3%). These results confirm that FBZ resistance in equine cyathostomins is present in France and that anthelmintic resistance to IVM is present in P. equorum. This study underlines the necessity to evaluate the efficacy of horse deworming strategies on a regular basis under field conditions.

Biological control using the fungi Duddingtonia flagrans against cyathostomins of horses

Gastrointestinal parasitism in horses can affect all categories with evident clinical signs. Control is made with the regular use of chemical products, which has cause resistance to all classes of drugs [1, 2]. New alternative control strategies are needed and biological control with the fungi Duddingtonia flagrans is an appropriate option. The fungi pass through the intestinal tract of the horse acting on the parasite free-living stages. The chlamydospores need to grow in particular environmental conditions for the hyphae to be able to predate the eggs and larvae [3]. The objective of this study was to evaluate the activity of D. flagrans against nematode parasites in naturally infected horses. The study was performed at the Sao Jose da Serra Stud in Pinhais, Brazil. Twenty Thoroughbred animals were divided based on their faecal egg count (EPG) values in 3 treatment groups and one control (n=5). Chlamydospores of a Brazilian isolate of the D. flagrans were orally administered together with grinded-corn at G1: 250.000, G2: 500.000, and G3: 1.000.000 per kilogram of live weight. The animals were treated daily during 5 days. Faecal samples were collected during the 5 days of treatment and 5 days after treatment for EPG counts, which was performed with a 1:25 concentration, individually, as well as the coproculture. Recovered larvae from coproculture were counted on triplicates from each sample, calculating the average and standard deviation. Statistical analysis was performed using Tukey test with GraphPad Prims 5 at 5% significance (P<0,05). The average EPG counts from all groups had a large (53%) daily variation during the experiment and did not show any statistical difference between groups (data not shown). Cyathostomum sp. was the predominant (above 94%) genus present at the faecal cultures in all groups. The fungi started to have an effect on the L3 stages 4 days after initiating the treatment reducing more than 97% (P<0.01) compared to the Control group. The predatory effect of the hyphae persisted for 4 days after the treatment was interrupted significantly (P<0.01) reducing larvae number (Figure 1). Duddingtonia flagrans showed a significant activity against infecting free-living larvae of Cyathostomins of horses.

Anthelmintic resistance in horse cyathostomins in France

common resistance patterns were pan-susceptible (38.2%), AUG-AMP-FOX-TIO-CHL-TET (16.6%), AUG-AMPFOX-TIO-CHL-TET-Timethoprim/sulfamethoxazole (SXT) (12.4%), AUG-AMP-FOX-TIO-CHL-TET-SXT-Gentamicin (GEN) (11.3%), and AMP-TIO-CHL-TET-SXT-GEN (7.6%). Although antimicrobial resistance among equine clinical Salmonella isolates did not increase for any drug and declined for several antimicrobial agents, multi-drug resistance was common in the region with 60.5% of isolates showing resistance to two or more drugs on the NARMS panel.

Drug Resistant Cyathostomins in Donkey Herds; Lessons in Management for All Equids

[3] Traversa D, von Samson-Himmelstjerna G, Demeler J, Milillo P, Schurmann S, Barnes H, Otranto D, Perrucci S, Frangipane di Regalbono A, Beraldo P, Boeckh A, Cobb R. Anthelmintic resistance in cyathostomin populations from horse yards in Italy, UK and Germany. 2009. Parasit Vectors 2: S2. [4] Traversa D, Castagna G, von Samson-Himmelstjerna G, Meloni S, Bartolini R, Geurden T, Pearce MC, Woringer E, Besognet B, Milillo P, D'Espois M. Efficacy of major anthelmintics against horse cyathostomins in France. 2012. Vet Parasitol, in press. [5] Rossano MG, Smith AR, Lyons ET. Shortened strongyle-type egg reappearance periods in naturally infected horses treated with moxidectin and failure of a larvicidal dose of fenbendazole to reduce fecal egg counts. Vet Parasitol 2010;173:349-52.

In vitro association of nematophagous fungi Duddingtonia flagrans (AC001), Monacrosporium thaumasium (NF34) and Pochonia chlamydosporia (VC1) to control horse cyathostomin (Nematoda: Strongylidae)

In vitro effects of nematophagous fungi Duddingtonia flagrans (AC001), Monacrosporium thaumasium (NF34) and Pochonia chlamydosporia (VC1) were evaluated against eggs and third-stage infective larvae (L3) of horse cyathostomin (Nematoda: Strongylidae). The following percentage reductions compared with the control group were observed after a 20-day exposure period: AC001, 61.6%; NF34, 66.1%; VC1, 73.2%; group AC001 + VC1, 86.8%; NF34 + VC1, 77.3%; AC001 + NF34, 92.4%. The results showed that the fungal isolates (VC1, AC001 and NF34), acting alone or in conjunction, were efficient in controlling horse cyathostomin under in vitro conditions.

Efficacy of major anthelmintics against horse cyathostomins in France

This paper reports a survey conducted in France during 2011 to evaluate the efficacy of commonly used anthelmintics against horse cyathostomins. A total of 40 farms and 1089 horses were screened for the presence of cyathostomins. All farms but one were positive, with an overall animal infection rate of 53.7%, ranging from 9% to 83% on individual farms. On 445 horses from 30 of these farms, a faecal egg count reduction test (FECRT) was performed to evaluate the efficacy of oral formulations of fenbendazole (FBZ), pyrantel embonate (PYR), ivermectin (IVM) and moxidectin (MOX). Calculation of the mean FECR and 95% confidence intervals (95% CI) around the mean was performed using bootstrap analysis. Resistance to FBZ was found on 17 of 18 farms investigated, with a mean reduction of 57% (95% CI: 38.5–71.2%). Suspected resistance for PYR was found on 6 of 30 farms, and confirmed on another 3 of 30 farms, with a mean reduction for PYR of 94.7% (95% CI: 88.9–98.5%). Reduced efficacy simultaneously of FBZ and PYR was found in 7 farms. Reduced efficacy of IVM was found in one animal on one farm and of MOX in one animal on another farm, and was combined with resistance against FBZ and/or PYR. These results indicate that single and multiple drug resistance and reduced efficacy in equine cyathostomins is present in France. Macrocylic lactones proved to be highly effective compounds against cyathostomins, with reduced efficacy for IVM and MOX in two farms only. These results extend present knowledge on the occurrence of drug resistant cyathostomins in Europe, and illustrate the necessity to use anthelmintics in appropriate worm control programmes.