The anthelmintic efficacy of cambendazole in horses

The anthelmintic activity of cambendazole 31% paste was evaluated in a controlled trial against naturally acquired gastro-intestinal parasites of the horse. Four groups of five adult horses were treated at dose rates of 0, 15, 20 and 25 mg/kg. The three dose levels of cambendazole tested were efficacious against the large strongyles Strongylus edentatus and S. vulgaris, the stomach worm Trichostrongylus axei, the pinworms Oxyuris equi and Probstmayria vivipara and all the species of small strongyles present. No efficacy was demonstrated against the tapeworm Anoplocephala perfoliata or the horse bots Gasterophilus intestinalis or G. nasalis     

Impaired efficacy of ivermectin against Parascaris equorum, and both ivermectin and pyrantel against strongyle infections in trotter foals in Finland

In order to assess the resistance situation against macrocyclic lactones in Parascaris equorum and against tetrahydropyrimidine derivatives in strongyles in Finnish trotter horses, 112 foals on 18 farms, mostly 1 year old, were examined for these parasites with a modified McMaster faecal flotation method. P. equorum positive foals (n=24) were given ivermectin orally at a dose of 200 μg/kg b.w., while strongyle positive but P. equorum negative foals (n=38) received pyrantel embonate orally at a dose of 19 mg/kg. Sixteen P. equorum infected foals, treated with ivermectin, also harboured strongyles. During the anthelmintic treatment visit to the farm, Faecal Egg Count Reduction Test (FECRT) reference (first) samples were collected. Fourteen days later, the second sampling (reduction samples) was done. The FECR was calculated for each foal/parasite combination. The reduction efficacies of ivermectin against P. equorum (mean 52%, calculated from the individual egg count reductions) and pyrantel against strongyles (43%) were strongly indicative of widespread resistance. Also indication of ivermectin resistance among strongyles was seen. The widespread use of anthelmintics for Finnish horses obviously has resulted in resistance, as has happened elsewhere, too.     

Efficacy of moxidectin and other anthelmintics against small strongyles in horses

Objective To compare the efficacy of moxidectin to ivermectin, oxibendazole and morantel against some gastrointestinal nematodes in horses.
Design Faecal egg count reduction after treatment.
Procedure A farm was selected where the population of small strongyles in horses was known to be resistant to oxibendazole. Horses were allocated to treatment groups based on faecal egg counts. After treatment, faecal samples were taken up to 109 days after treatment and faecal egg counts estimated. Faecal cultures were used to estimate the contribution of small and large strongyles to the faecal egg counts at each sampling.
Results Moxidectin (0.4 mg/kg) suppressed faecal egg counts for 109 days after treatment in most horses compared to 40 days with ivermectin (0.2 mg/kg), 13 days with morantel (9.4 mg/kg) and less than 13 days with oxibendazole (10 mg/kg). Most of the faecal egg count was attributable to small strongyles based on faecal culture, although Strongylus vulgaris was present in some samples in low numbers. Oxibendazole resistance in small strongyles was confirmed and a less than expected efficacy of morantel was also seen.
Conclusion Moxidectin was highly effective in reducing faecal egg counts after treatment for at least 12 weeks and up to 16 weeks in most horses. These horses were infected with a population of small strongyles known to be resistant to oxibendazole and possibly morantel. The duration of the reduction in faecal egg counts after treatment with moxidectin (0.4 mg/kg) was at least twice that of ivermectin (0.2 mg/kg) and greater than four times that for morantel and oxibendazole.     

Benzimidazole resistance of equine strongyles: critical tests of several classes of compounds against population B strongyles from 1977 to 1981

From 1977 to 1981, critical tests were conducted on 10 horses naturally infected with population B strongyles. Drugs tested were: oxibendazole (OBZ), 10 mg/kg of body weight (n = 1); albendazole, 10 mg/kg (n = 1); a mixture of thiabendazole (TBZ), 44 mg/kg and trichlorfon, 40 mg/kg (n = 1); a mixture of TBZ at 44 mg/kg with piperazine (PPZ) at 55 mg of base/kg (n = 1); febantel (FBT), 6 mg/kg (n = 3), 12 mg/kg (n = 1), or 24 mg/kg (n = 1); and pyrantel (PRT) pamoate, 6.6 mg of base/kg (n = 1). Large strongyles, Strongylus vulgaris (9 horses) and S edentatus (5 horses), were effectively removed (100%) by each compound and mixture. Five species of small strongyles (Cyathostomum catinatum, Cyathostomum coronatum, Cylicocyclus nassatus, Cylicostephanus goldi, and Cylicostephanus longibursatus), previously singled out in this population as resistant to 5 benzimidazoles (TBZ, mebendazole, cambendazole, fenbendazole, and oxfendazole), but not OBZ, were efficaciously removed by OBZ, albendazole, the mixture of TBZ plus PPZ, FBT (24 mg/kg), or PRT. These 5 small strongyle species were resistant to FBT (6 mg/kg) in 3 foals and Cylicostephanus minutus was also resistant in 2 of 3 foals to FBT (6 mg/kg). Doubling the dose of FBT to 12 mg/kg increased the average removal of the 5 basic species plus Cylicostephanus minutus to 88%. The mixture of TBZ and trichlorfon was relatively ineffective against 3 species (C catinatum, C coronatum, and Cylicostephanus longibursatus), but unexpectedly efficacious (86% to 99%) for 2 species (Cylicocyclus nassatus and Cylicostephanus goldi).(ABSTRACT TRUNCATED AT 250 WORDS)     

Re-evaluation of ivermectin efficacy against equine gastrointestinal parasites.

Two trials were conducted to confirm the efficacy of ivermectin paste against endoparasites of horses. In these trials, 20 ponies were treated with ivermectin oral paste at 200 mcg x kg body weight once on Day 0, and 20 ponies served as unmedicated controls. The animals carried naturally acquired parasite infections as confirmed by pretrial fecal examination. The animals were necropsied for worm recovery on Days 14, 15 or 16. Parasites recovered were identified to species. Horses treated with ivermectin had significantly (P<0.05) fewer (>99.0% reduction) adult small strongyles (Coronocyclus spp including C. coronatus, C. labiatus, C. labratus; Cyathostomum spp including C. catinatum, C. pateratum; Cylicocyclus spp including C. ashworthi, C. elongatus, C. insigne, C. leptostomum, C. nassatus, C. radiatus; Cylicodontophorus bicoronatus; Cylicostephanus spp including C. asymetricus, C. bidentatus, C. calicatus, C. goldi, C. longibursatus, C. minutus; Gyalocephalus capitatus; Parapoteriostomum spp including P. euproctus, P. mettami; Petrovinema poculatum; Poteriostomum spp including P. imparidentatum, P. ratzii) and adult large strongyles (Strongylus edentatus, S. vulgaris; Triodontophorus spp including T. brevicauda, T. serratus; Craterostomum acuticaudatum) than the controls. Ivermectin was also highly effective (94% to >99%, P<0.05-0.01) against Gasterophilus intestinalis larvae, Habronema spp., Oxyuris equi, Parascaris equorum. The data from these two trials confirm that ivermectin paste administered to horses orally at 200mcg x kg(-1) continues to be highly effective for treatment and control of a broad range of small and large strongyle species as well as other species of gastrointestinal parasites.     

A multicenter evaluation of the effectiveness of Quest Gel (2% moxidectin) against parasites infecting equids

Controlled trials with a common protocol were conducted in Idaho, Illinois and Tennessee to evaluate anthelmintic effectiveness of Quest Gel (QG; 2% moxidectin) against lumenal parasites in horses. Candidate horses were required to have naturally acquired nematode infections, as confirmed by presence of strongylid eggs in feces. At each site, 24 equids were blocked on the basis of pretreatment strongyle fecal egg counts (EPG) and randomly assigned to treatments within blocks. Within each block of two animals, one received QG on Day 0 at a dosage of 0.4 mg moxidectin/kg b.w. and one was an untreated control. Body weights measured the day before treatment served as the basis for calculating treatment doses. Horses assigned to treatment with QG received the prescribed dose administered orally with the commercially packaged Sure Dial syringe. Horses were necropsied 12-14 days after treatment, and lumenal parasites and digesta were harvested separately from each of five organs, including the stomach, small intestine, cecum, ventral colon and dorsal colon. Parasites from stomachs and small intestines were identified to genus, species and stage. Micro- (i.e., < 1.5 cm) and macroparasites (i.e., > 1.5 cm) in aliquots from the cecum, ventral colon and dorsal colon were examined in aliquots of approximately 200 parasites until at least 600 parasites had been identified to genus, species and stage or until all parasites in the 5% aliquot were examined, whichever occurred first. Data were combined across sites and analyzed by mixed model analysis of variance to assess the fixed effect of treatment and random effects of site and block within site. Because QG does not contain a cestocide, efficacy of QG against tapeworms was not significant (P > 0.05). Based on geometric means, however, efficacy of QG was greater than 90% (P < 0.05) against 38 species and developmental stages of cyathostomes, strongyles, bots, larval pinworms and ascarids encountered in at least 6 of 36 control horses in the combined data set. None of the horses treated with moxidectin exhibited evidence of adverse effects. Study results demonstrate QG, administered to horses with naturally acquired endoparasite infections at a dosage of 0.4 mg moxidectin/kg b.w., was highly effective against a broad range of equine parasitic infections.     

Antiparasitic activity of an ivermectin and praziquantel combination paste in horses

Modern anthelmintic use in horses has decreased the prevalence of the large strongyles, which has in turn shifted the focus of parasitologists to the pathogenic importance of the small strongyles, tapeworms, and other parasites. These studies show that a combination product containing ivermectin and praziquantel allowed efficacious treatment of horses for nematode, cestode, and bot infections. The use of this combination product may be of special benefit to horses that are mainly kept outdoors and on grazing pastures.     

Treatment of equine onchocerciasis with ivermectin paste

SUMMARY A single oral dose of ivermectin paste was administered to 12 horses with dermatitis and clinical signs typical of onchocerciasis. Two of the horses also had lesions of Queensland itch. Microfilarias of Onchocerca cervicalis were identified in fresh, macerated, skin biopsies from the neck, brisket or umbilical regions of all horses and microfilarias of O. gutturosa from the neck of 2. Eight of the horses developed skin reactions 4 to 24 h after the administration of the ivermectin, notably weals over the neck, shoulders and flanks and pitting oedema of the ventral midline and intermandibular space. Regression of the onchocerciasis lesions was evident within 7 days of treatment and affected skin had returned to normal within 3 months. The lesions of Queensland itch were not affected by the ivermectin treatment. Microfilarias were present in biopsies of skin, particularly in the superficial dermis, before treatment, but were absent from all skin biopsies taken one week after treatment. In some horses transient skin sensitivity reactions developed. Microfilarias began to reappear in the biopsies of some of the horses 2 months after treatment. It is concluded that the oral paste formulation of ivermectin, although not effective against adult onchocerca, is useful for the therapeutic control of microfilarias in the skin lesions of equine onchocerciasis.     

Kinetics of natural expulsion of some equine parasites during a critical test

An experiment was conducted to determine the rate(s) of natural elimination of some equine parasites from nine nontreated horses during the interim of a critical test. During the 7-day period 0.08% of the small strongyles and 0.4% of the Gastrophilus (bot) populations were concluded that natural elimination of large strongyles, small strongyles, and Gastrophilus larvae during the interim of the critical test, would not have biased the efficacy of an anthelmintic or boticide.     

Comparative long-term efficacy of ivermectin and moxidectin over winter in Canadian horses treated at removal from pastures for winter housing

The impact of a late fall treatment on the spring rise of fecal egg counts was evaluated in a controlled study with Canadian horses treated with 2 different dewormers immediately after removal from pasture for winter housing. The horses were stabled until the end of the trial period. Seventeen weanlings, 20 yearlings, and 15 2-year-old horses located in Ontario, which were presumed to be naturally infected with cyathostomins after pasture grazing, were randomly allocated to either a group treated with 0.4 mg/kg of moxidectin and 2.5 mg/kg of praziquantel or a group treated with 0.2 mg/kg of ivermectin and 1.5 mg/kg of praziquantel. Three weeks after treatment, all strongyle fecal egg counts were reduced to zero for both treatment groups. However, at 5 months post-treatment, mean geometric fecal egg counts were statistically higher for the yearlings and 2-year-old horses treated with ivermectin than for the yearlings and 2-year-old horses treated with moxidectin (P < 0.0001).     

Efficacy of an oxibendazole-trichlorfon paste formulation against third stage larvae of Gasterophilus intestinalis and its safety in horses

A paste formulation containing 14.3 per cent of oxibendazole and 44 per cent of trichlorfon was administered to 33 ponies and horses. The dose rate used was equivalent to 10 mg and 30 mg/kg bodyweight, of oxibendazole and trichlorfon respectively. After treatment 25 animals passed between one and 82 third stage larvae of Gasterophilus intestinalis in their faeces. Dosing with 0.2 mg ivermectin/kg bodyweight three weeks later resulted in six animals expelling between one and four bots. The efficacy of the oxibendazole-trichlorfon paste was on average 96.2 per cent. This drug combination given to 52 ponies and horses at the indicated dose rate and to six ponies at twice that dose was tolerated without side effects except transient softening of the faeces in several animals and mild symptoms of colic in two horses.     

Efficacy of ivermectin (22,23-dihydroavermectin B1) against gastrointestinal parasites in ponies

The controlled test method was used to evaluate the antiparasitic efficacy of IM inoculated 22,23-dihydroavermectin B1 (ivermectin) against gastrointestinal parasites of horses (ponies). Parasite infections were naturally acquired in southern Louisiana. Dose levels of the drug tested were 0.2 mg/kg, 0.3 mg/kg, and 0.5 mg/kg. Ivermectin at all dose levels tested had an efficacy greater than 97% (P less than 0.05) against Gasterophilus intestinalis larvae, Trichostrongylus axei, Oxyuris equi larvae, Strongylus vulgaris, S edentatus, 15 species of small strongyles, and small strongyle larvae. Ponies were less uniformly infected with Habronema sp larvae, G nasalis larvae, Parascaris equorum, O equi adults, Anoplocephala perfoliata, S equinus, and 11 small strongyle species, and statistical analysis was not possible to do. However, observations indicate that the drug was also highly effective against these species. There were no gross or clinical reactions observed in treated animals. Dissections of the injection sites revealed spindle-shaped lesions, 3 to 5 cm long, in a few ponies in all treatment groups, including those given the placebo injection.     

Benzimidazole resistance of equine stronygles--critical tests of six compounds against population B

Critical tests were conducted on eight horses naturally infected with several species of large and small strongyles from population B. Tested were six benzimidazoles, including thiabendazole (2 lots) (44 mg/kg of body weight); mebendazole (8.8 mg/kg); cambendazole (two formulations) (20 mg/kg); fenbendazole (10 mg/kg); oxibendazole (10 mg/kg); and oxfendazole (10 mg/kg). All compounds were administered by stomach tube except one of the two cambendazole formulations which was an intraoral paste. Removal of large strongyles (when present), Strongylus vulgaris and Strongylus edentatus, was 100% by each drug. In general, five species of small strongyles (Cyathostomum catinatum, Cyathostomum coronatum, Cylicocyclus nassatus, Cylicostephanus goldi, and Cylicostephanus longibursatus) exhibited varying degrees of resistance (% removal) to all of the drugs except oxibendazole. A total of 19 other species of small strongyles from seven genera, including the three described earlier were about 100% removed by the six benzimidazoles. Poor removal of immature (fourth-stage larvae) forms was also characteristic of the six drugs.     

The anthelmintic efficacy of ivermectin in experimentally infected cattle

The 22,23-dihydro derivative (ivermectin) of the major B₁ components of the avermectins was evaluated, by oral and parenteral routes, for anthelmintic activity in cattle experimentally infected with 7 gastro-intestinal nematode species and lungworm. Treatment at three dosage levels was administered when the parasites were in the L₄ developmental stage or when adult. The dosage expected to remove 95% of the nematodes (ED₉₅) by each route of administration against the various developmental stages of each species of parasite was calculated by methods of linear regression to choose dose levels to be used in subsequent developmental field trials. Parenterally, efficacy against L₄ stages of Haemonchus placei, Ostertagia ostertagi, Trichostrongylus axei, T. colubriformis, Cooperia oncophora, C. punctata, Oesophagostomum radiatum and Dictyocaulus viviparus exceeded 99% with treatment at 0.2 mg ivermectin/kg. Parenteral treatment of the adult parasites resulted in at least 98% reduction of worm burdens, except $\text{? 90\%}$ for T. colubriformis, with 0.2 mg/kg. Oral treatment of L₄ stages of development with 0.2 mg/kg resulted in at least a 95% reduction in worm burdens of each of the 8 species of parasite. Oral treatment of the adult worms with 0.1 mg ivermectin/kg produced at least a 98% decrease in each parasite species, except for T. colubriformis (90% reduction) for which dose-response calculations suggest 95% efficacy with oral treatment at 0.2 mg/kg.     

Field efficacy of ivermectin plus praziquantel oral paste against naturally acquired gastrointestinal nematodes and cestodes of horses in North America and Europe

The efficacy of an oral formulation of ivermectin plus praziquantel in the reduction of nematode and cestode egg counts in horses was assessed in 273 horses under field conditions at 15 sites in North America (n = 6) and Europe (n = 9). Horses were confirmed by fecal examination to have natural infections of strongyles (100%) and tapeworms (76%). Replicates of four horses were formed at each site, and in each replicate three animals received ivermectin (0.2 mg/kg body weight) plus praziquantel (1 mg/kg body weight) oral paste and one animal remained untreated or received vehicle paste. Fecal samples were collected for fecal nematode and cestode egg counting before and 7, 8, 9, 14, 15, and 16 days after treatment. Horses treated with ivermectin plus praziquantel oral paste had significantly (P <.01) lower posttreatment strongylid and cestode egg counts (reductions of 98% or more) than controls. Combined site analyses revealed that 95% or 96% of the horses positive for cestode eggs before treatment that were treated with ivermectin plus praziquantel were negative for cestode eggs at each posttreatment fecal examination. No adverse reactions attributable to ivermectin plus praziquantel oral paste treatments were observed. The results of the studies demonstrated that ivermectin plus praziquantel paste was highly effective in reducing egg shedding by gastrointestinal nematodes and cestodes, and no adverse reactions were observed in horses treated under field conditions.     

Critical tests and safety studies on trichlorfon as an antiparasitic agent in the horse.

Three series of critical tests were completed on a combined total of 46 horses to determine the efficacy of single doses of trichlorfon against bots, ascarids, pinworms, and large strongyles. Different formulations of trichlorfon were administered by tubing intragastrically, mixing with the daily grain ration, injecting intramuscularly, or pouring on the back at dose rates between 20 and 100 mg/kg. Administration by feeding tended to be more efficacious for removal of bots and less toxic to the horese than administration by stomach tube. In many of the tests, trichlorfon was given in the grain ration at the dose rate of 40 mg/kg of body weight, and the aggregate average removals of 2nd and 3rd instars of Gastrophilus intestinalis and Gasterophilus nasalis in the 3 series of tests were between 97 and 100%. Removal of Parascaris equorum was equally efficacious with both the intubation and the grain feeding methods of dosing, and at the dose rate of 40 mg/kg, the aggregate averages were 99 and 100% in the 3 series. Removal of Oxyuris equi was variable--aggregate averages were between 11 (1 infected horse in the initial series) and 96 (5 infected horses in the 3rd series) to 100% (7 infected horses in the 2nd series). Large strongyles, Strongylus vulgaris and Strongylus edentatus were almost completely refractory to the 40-mg/kg dose rate of trichlorfon. Dose rates of 40 mg/kg and less were generally well tolerated by the critical test horses. Higher dose rates (60 and 80 mg/kg) administered by stomach tube induced moderately severe to severe colic and diarrhea, whereas a dose of 80 mg/kg given in the feed resulted in only a transient softening of the feces. Likewise, 5 consecutive doses, 1 week between doses, of a bolus formulation given at the rate of 80 mg/kg to 4 horses were well tolerated. Clinical trials involving a total of 2,294 treatments of trichlorfon at dose rate of 35 to 40 mg/kg in pregnant and nonpregnant mares, stallions, suckling and weanling foals, yearlings, and horses in training on 38 farms in central Kentucky did not cause notable adverse clinical effects.     

Comparison of ivermectin, oxibendazole, and pyrantel pamoate in suppressing fecal egg output in horses

Thirty resident horses at a boarding stable in Alberta were used to evaluate the relative efficacies of ivermectin, oxibendazole, and pyrantel pamoate in reducing fecal egg output in adult horses under routine management conditions during spring and early summer, and to more clearly define the duration of suppression of fecal egg production following anthelmintic treatment. Horses were blocked according to pretreatment egg counts and randomly assigned to one of three treatments: pyrantel pamoate at 6.6 mg/kg body weight; oxibendazole at 10 mg/kg body weight; or ivermectin at 200 μg/kg body weight. All treatments were administered orally as a paste on day 0.Fecal samples were collected for examination by the modified Wisconsin procedure before treatment, and then at 4-11 day intervals up to day 72.

Very few if any strongyle eggs were found in the feces of any horses up to day 35. On days 42, 50 and 57, the geometric mean egg count for the ivermectin group was significantly (p<0.05) lower than that for the oxibendazole or pyrantel pamoate groups. Based on a survival curve analysis of the data, the mean number of days for recurrence of eggs in the feces was significantly longer for the ivermectin group than for the oxibendazole and pyrantel pamoate groups.

Under conditions encountered in this study, the posttreatment interval to resumption of fecal egg out-put in horses treated with ivermectin was eight to nine weeks, compared with five to six weeks for horses treated with oxibendazole or pyrantel pamoate.

     

Efficacy of Ivermectin Pour-on Against Nematodes Infecting Foals on Pasture: Coprological and Biochemical Analysis

The efficacy of topical ivermectin (IVM) on foals naturally infected by parasitic nematodes was evaluated. Two dosages of IVM were applied pour-on (F-Nor0.5; 0.5 mg/kg body weight [BW] and F-Nor1; 1 mg/kg BW) and results compared with the oral administration (F-Eq0.2; 0.2 mg/kg BW of IVM). The efficacy was measured by estimating the reduction in the fecal egg counts (fecal egg count reduction) and in the numbers of horses shedding parasite eggs (positive horse reduction). Several biochemical and enzymatic serum parameters were measured in the groups F-Eq0.2 and F-Nor1. Before the deworming of the horses, eggs of Parascaris equorum, Cyathostomum, Gyalocephalus spp, and Oxyuris equi were identified. In all the treated groups, the excretion of ascarid eggs ended 4 days after the treatment. The orally administered IVM suppressed the egg output of strongyles and pinworms 4 days after the treatment, whereas for the F-Nor1 group this occurred 8 days after the treatment. Eggs of strongyles were detected in the F-Nor0.5 group throughout the study. The levels of blood urea nitrogen, creatinine, total proteins, albumin, globulins, and lactate dehydrogenase (LDH) reduced significantly after the administration of IVM, but values not within the normal range were only achieved for LDH. A significant positive correlation between the fecal egg output of cyathostomins and the LDH was investigated. Clinically, no adverse reactions in the horses receiving the topical IVM were observed. It was concluded that the pour-on administration of 1 mg/kg BW IVM provides similar results to the oral administration, and offers a very useful tool to control infestation by the intestinal nematodes affecting wild grazing horses.     

The comparative efficacy of four broad spectrum anthelmintics against some experimentally induced trichostrongylid infections in sheep and goats

A controlled slaughter trial was undertaken to compare the efficacies of oxfendazole (5 mg/kg), morantel citrate (10 mg/kg), levamisole (8 mg/kg) and ivermectin (0.2 mg/kg) against experimentally induced infections of adult Haemonchus contortus, Ostertagia spp., Trichostrongylus colubriformis and Cooperiacurticei in sheep and goats. Ivermectin and oxfendazole achieved similar levels of efficacy in both hosts against all four worm genera as did levamisole and mortantel against H. contortus and C. curticei. Against Ostertagia spp. and T. colubriformis, however, the latter two drugs were less effective in goats than sheep. Neither the numbers of Ostertagia spp. removed from goats by levamisole (81% reduction) nor the numbers of T. colubriformis removed from goats by morantel (56% reduction) were statistically significant (P>0.05).     

Larval cyathostomiasis.

Over the past few years, cyathostomiasis has become increasingly recognized as a clinical problem of horses in the United States. Clinical cyathostomiasis has been reported frequently in Europe for a considerable time. This clinical syndrome is usually related to the sudden release of large numbers of the larval stages of small strongyles from the mucosa of the large intestine. Typical clinical signs include diarrhea, ventral abdominal edema, pyrexia, colic, weight loss, and poor body condition. Hypoalbuminemia and the presence of large numbers of small strongyles being passed in the feces are also characteristic features of the disease. The disease may occur seasonally in late winter and early spring or after drug treatment to remove the luminal stages of small strongyles. Two commercially available drugs, moxidectin and fenbendazole, have been shown to be effective against the encysted larval stages of the parasites. Drug resistance of small strongyles to all classes of currently available antiparasitic compounds except the macrocyclic lactones (ivermectin and moxidectin) is a limiting factor in controlling these parasites and may result in an increased prevalence of clinical cyathostomiasis over time.