Morantel Tartrate Research Articles

곰솔(Pinus thunbergii)에서 소나무재선충(Bersaphelenchus xylophilus) 나무주사 약제의 효율적인 평가법 개발

Pine wood nematode (PWN), Bursaphelenchus xylophilus is one of the most serious pests of pine tree. Trunk injection of some nematicides in tree is well known as an effective control method. However there are some limitating factors which hindering the efficacy of trunk injection in field or potted tree. In this study we suggested easy and useful alternative screening methods of nematicides against PWN. Reproduction of PWN was influenced by tree twig moisture (high reproduction in high moisture trig) and paraffin coating was 78.6% reduced moisture loss in tested twig. There were no reproduction different in up and down site from infection site of twig at 1 month after inoculation of PWN and also distance (5 and 10 cm) from inoculation site of PWN did not influence the reproduction of PWN. Numbers of reproduced PWN were higher with decreasing diameter of twig. Numbers of reproduced PWN were similar to P. thunbergii and P. densiflora. However reproduction was increased depending on high inoculation density and longer propagation period. When inoculation of PWN on cut twig injected with emamectin benzoate 2.15% EC and morantel tartrate 8% SL in trunk of Pinus thunbergii in the field, PWN number were significantly reduced than untreated control. We suggest this screening method for PWN control agents.

Nematicidal activity against Bursaphelenchus xylophilus of isoobtusilactone A isolated from Persea americana

Abstract Methanol extracts of 50 plant species were assessed for nematicidal activity against the pine wood nematode (PWN), Bursaphelenchus xylophilus. Out of these, five extracts: Justicia diclipteroides subsp. usambarica; Nerium oleander; Persea americana; Scadoxus multiflorus subsp. multiflorus; and Thespesia populnea, caused 96-100% mortalities of pine wood nematode at 1000 μg ml–1 for 48 h. Methanol extract of the stem bark of P. americana (avocado) and the n-hexane layer obtained from the methanol extract by solvent partitioning caused 100% mortality of PWN at low concentrations of 125 and 63 μg ml–1, respectively. One potent nematicidal compound was isolated from the stem bark of P. americana and its chemical structure was determined to be isoobtusilactone A (1) by mass and NMR spectral analyses. The chemical showed a very strong nematicidal activity against PWN; it caused mortalities of over 97% at concentrations higher than 50 μg ml–1. Compared with a commercial synthetic nematicide, morantel tartrate, compound 1 showed a little more potent activity. The results suggested that compound 1 may have the potential to be explored as a natural nematicide or be useful as a lead molecule for development of new nematicidal agents for controlling the pine wilt disease caused by B. xylophilus.

Fenbendazole stimulates interferon secretion in calves during viral infection

A total of six trials (five with live animals and one in vitro study) were conducted to evaluate the effects of fenbendazole (FBZ) on the immune response in stressed feedlot cattle. FBZ was given to all treatment calves at the recommended label dosage of 2.3 mg/lb (5 mg/kg) body weight. In Trial 1, treatment with FBZ did not affect serum neutralizing (SN) virus titers or viral shedding following inoculation with live, avirulent bovine herpes virus (BHV-1), but did increase titers for interferon (IFN) in nasal secretions at one, four and seven days post-inoculation. In Trial 2, FBZ-treatment reduced viral shedding and increased IFN titer in nasal secretions on days 4, 7 and 11 following inoculation with live, virulent bovine viral diarrhea virus (BVDV). In Trial 3, treatment with FBZ increased average daily gain ( P =0.11) and increased IFN titer in nasal secretions at two ( P =0.12) and seven ( P =0.07) days following intranasal vaccination with avirulent BHV-1. In naturally infected calves, control and FBZ-treated calves had greater nasal secretions of IFN compared to calves treated with morantel tartrate, levamisole, or thiabendazole (Trial 4). Treatment with FBZ did not increase weight gain or interferon secretions in response to vaccination with IBR and BVD viruses (Trial 5). In cell cultures treated with bluetongue virus, FBZ increased IFN titers. FBZ appears to stimulate IFN secretion in calves during experimental infection with either BHV-1 or BVDV (Trial 6).

Nematicidal Activity of Plant Essential Oils against Bursaphelenchus xylophilus (Nematoda: Aphelenchoididae)

The nematicidal activity and poisoning symptoms of 88 plant essential oils against Bursaphelenchus xylophilus were examined by an immersion bioassay. Results were compared with those of three trunk-injection nematicides: fenitrithion, levamisol hydrochloride, and morantel tartrate. As judged by 24 h LC 50 values, cinnamon bark oil (0.12 mg/ml) was the most effective nematicide, followed by coriander herb oil (0.14 mg/ml). Potent nematicidal activity was also observed with lemongrass, oregano, thyme red, and clove bud oils (LC 50, 0.57-0.88 mg/ml). Fenitrothion was ineffective (LC 50, > 10 mg/ml). In typical poisoning symptoms in B. xylophilus, these essential oils exerted rapid nematicidal action and the nematodes killed usually showed an extended shape, whereas levamisole hydrochloride and morantel tartrate usually exhibited semicircular and coiling shapes, respectively. The essential oils described merit further study as botanical nematicides for the control of pine wilt disease caused by B. xylophilus.

Anthelmintic resistance on goat farms in Georgia: efficacy of anthelmintics against gastrointestinal nematodes in two selected goat herds

Gastrointestinal nematode (GIN) parasitism is a major constraint to production of goats in the southeastern United States. The conventional method of control used by producers in this region is frequent use of anthelmintics during the warm season. Overuse of anthelmintics has led to an increase in the incidence of anthelmintic resistance in many parts of the world, but data on prevalence of anthelmintic resistance in GIN of goats in the southeastern United States are very limited. To address this issue, anthelmintic efficacy was determined in goat herds at the Fort Valley State University, Agricultural Research Station (FVSU-ARS) and the University of Georgia, College of Veterinary Medicine (UGA-CVM) using fecal egg count reduction (FECR) tests and DrenchRite ® larval development assays (LDA). At FVSU-ARS, 2-year-old Spanish goat does were randomly allocated to one of nine different treatment groups ( n=10): albendazole (ABZ; 20 mg/kg body weight (BW)), fenbendazole (FBZ; 20 mg/kg BW), ivermectin (IVM; 0.4 mg/kg BW), doramectin (DRM; 0.4 mg/kg BW), moxidectin (MOX; 0.4 mg/kg BW), levamisole (LEV; 12 mg/kg BW), morantel tartrate (MOR; 10 mg/kg BW), a combination of IVM (0.4 mg/kg BW) and ABZ (20 mg/kg BW), and untreated controls. At UGA-CVM, goats were randomly allocated to one of five different treatment groups ( n=8): ABZ (20 mg/kg BW), IVM (0.4 mg/kg BW), MOX (0.4 mg/kg BW), LEV (12 mg/kg BW), and untreated controls. All drugs in both experiments were administered orally. Anthelmintic efficacy was calculated by comparing 14-day post-treatment FEC of treated and control animals, and percent reductions were interpreted using the World Association for the Advancement of Veterinary Parasitology guidelines for resistance. For the LDA, nematode eggs were isolated from pooled fecal samples of untreated control goats in each herd and used to perform DrenchRite ® assays. In the FVSU-ARS herd, MOX, LEV, the combination of IVM and ABZ, IVM, DRM, ABZ, MOR, and FBZ reduced FEC by 100, 91, 88, 78, 76, 62, 48, and 10%, respectively. In the UGA-CVM herd, MOX, LEV, ABZ and IVM, reduced FEC by 100, 94, 87, and 0%, respectively. In both herds moxidectin was the only drug tested that was fully effective. Results of the LDA were in agreement with results of the FECR tests for both herds. These data demonstrate the presence of GINs resistant to all three major anthelmintic classes in both goat herds.

Gastrointestinal and pulmonary nematode infections decrease goat productivity in Moroccan semi-arid conditions.

A herd of goats naturally infected with lungworm and gastrointestinal nematodes was divided into three groups and treated with either morantel tartrate or fenbendazole at strategic periods, i.e. in June (at pre-mating), in November (at pre-kidding) and in January (at early lactation) or left untreated. Morantel tartrate treatment (8 mg kg-1) was efficient in reducing the gastrointestinal nematode egg output and fenbendazole treatment (15 mg kg-1) was efficient in reducing the gastrointestinal nematode egg and small lungworm larvae faecal output. Reductions in mortality of adult goats and their progeny and improvement of rearing percentages were recorded in both treated groups, with fenbendazole showing a greater response than morantel tartrate. A relative risk analysis showed that mortality in goats and kids was significantly reduced in treated kids and goats. Reduction of 6.6% in kidding rates, 0.21 in prolificacy, and an increase of 1.3 in abortion rates, 8.3% in kid and 2.2% in goat mortalities, could be attributable to the small lungworm infection. Small lungworm infections seem therefore to be one of the main causes of indirect kid mortality and inadequate breeding performance of goats in the semi-arid Middle Atlas region of Morocco.

Anthelmintic treatment strategies: current status and future

Despite the array of anthelmintics and endectocides and delivery systems available for use in the prevention and control of nematode parasites of ruminants, the number of highly effective control programs that have been developed and even the number of such programs that have been successfully implemented in commercial animal production, there have been no recent innovations or discoveries in regard to strategies, new anthelmintics, or systems for controlling nematode parasites through anthelmintic use. In the traditional sense of chemotherapy-chemoprophylaxis, we have probably achieved the maximum effect of what is possible from excellent anthelmintics developed by the pharmaceutical industry over the last 35 years, i.e. from thiabendazole through levamisole and morantel tartrate, to more advanced benzimidazoles and to the avermectins and milbemycins. At the core of all anthelmintic treatment-related problems is the lingering conception among a large body of animal producers that anthelmintic treatment is the only effort needed to control parasitism and its effects on host animals. This concept has given rise to the long-standing difficulty of drug resistance in sheep nematodes and the not remote possibility of its development in nematodes of cattle. Along with this are serious concerns over environmental toxicity, tissue residues and enormous financial investment to develop new and novel anthelmintic compounds. Progress is being made in current and intensive searches for development and testing of control approaches alternative to anthelmintics, e.g. helminth vaccines, biological control agents such as fungi, selection of resistant sires, alternative chemicals and nematode growth regulators. A timetable for when alternative controls can be developed fully and put into practical use cannot be predicted. It is universally acknowledged among parasitologists that existing anthelmintics must be preserved and utilized judiciously to ensure continued effectiveness. A major example is to be found in strategic or integrated control programs in Australia developed over the last 10 years to combat widespread drug resistance in sheep. Major imperatives for future programs and systems of controlling nematode parasites of ruminants are improved means of getting producers to adopt proven and sustainable methods.

Dietary Intake Estimates as a Means to the Harmonization of Maximum Residue Levels for Veterinary Drugs: II. Proposed Application to the Free Trade Agreement between the United States and Canada

The Free Trade Agreement between the United States and Canada (FTA) went into effect January 1, 1989. To implement certain provisions of the agreement on technical regulations and standards, the United States Food and Drug Administration's Center for Veterinary Medicine, Health and Welfare Canada's Bureau of Veterinary Drugs, and Agriculture Canada established the Working Group on Veterinary Drug Tolerances. The progress of the working group and its continuing efforts to harmonize tolerances for approximately 15 veterinary drugs are discussed. This paper proposes use of the toxicologically determined acceptable daily intake (ADI) for the drug as the safety standard for reaching conclusions on the acceptability of residues in meat for human consumption. Specifically, the “equivalence” of different MRLs for the same veterinary drug would be determined by considering whether they are likely to result in dietary residues that exceed the other country's ADI for the drug. Estimates are made for the veterinary drugs lasalocid, fenbendazole, morantel tartrate, halofuginone, and tilmicosin. Based on these estimates, the U.S. and Canadian MRLs for each drug would be considered equivalent for trade purposes.

Improved bioassay for estimation of inhibitory effects of ovine gastrointestinal mucus and anthelmintics on nematode larval migration

A bioassay based on the ability of substances present in ovine gastrointestinal mucus or anthelmintics to paralyse third stage larval (L3) nematodes and inhibit their passage through 20 μm nylon mesh sieves [larval migration inhibition (LMI) activity] is described. Factors influencing the reproducibility of the bioassay were examined using exsheathed L3 of the sheep gastrointestinal nematode parasite Trichostrongylus colubriformis. Levamisole, morantel tartrate and piperazine were shown to inhibit L3 migration in the bioassay. The bioassay was used to demonstrate that gastrointestinal mucus from nematode-resistant sheep possessed greater L3 inhibitory activity than mucus from nematode-susceptible sheep. LMI activity of mucus used in this bioassay was significantly correlated with LMI activities obtained using two previously described similar bioassays. The action of mucus components on nematode larvae was shown to be reversible in the bioassay. The modified assay has advantages over other bioassays as it avoided the use of temperature-dependent agar blocks, reduced the number of L3 required to a more manageable size, and the whole experiment could be performed on a 48-well culture plate. The reproducibility, high correlation with other bioassays, ease of performance, suitability for testing a large number of samples and low cost make this modified assay the method of choice for determining antiparasitic activity of gastrointestinal mucus components and as a screen for potential anthelmintics.

The effects of anthelmintics on ovine larval nematode parasite migration in vitro

The anthelmintics ivermectin, levamisole, morantel tartrate and thiabendazole all inhibited, in vitro, the motility of third stage larvae (L3) of Trichostrongylus colubriformis. The bioassay, based on the inhibition of L3 migration from agar gels, yielded sigmoid dose-response curves for ivermectin, levamisole and morantel tartrate, but not thiabendazole. The concentration of levamisole giving 50% inhibition of migration (EC50) was determined for Cooperia curticei, Haemonchus contortus, Nematodirus spathiger, Ostertagia circumcincta, Trichostrongylus axei, T. colubriformis and T. vitrinus. EC50s differed between species but within species the EC50s for ensheathed and exsheathed L3 were similar except for N. spathiger which showed significantly higher EC50 for the ensheathed L3. No difference between EC50s for levamisole-resistant and susceptible strains of T. colubriformis were found. Similarly, morantel-resistant and susceptible stains of T. colubriformis could not be differentiated in this bioassay. The inhibition of L3 motility by known anthelmintic compounds in this bioassay suggests that the bioassay could be used as a screen for potential new anthelmintics.

Pharmacodynamics, pharmacokinetics and faecal persistence of morantel in cattle and goats

Morantel could not be detected (< 0.05 microgram/ml) in the plasma of cattle or goats following the oral administration of morantel tartrate at a dose rate of 10 mg/kg bodyweight. No morantel was detected in the milk of lactating goats except in one animal where a concentration of 0.092 microgram/ml was detected at 8 h after drug administration. Morantel was highly effective against Cooperia oncophora infections in calves treated 6, 9 or 18 days after infection; however, was highly effective against Ostertagia ostertagi only when treated 18 days after infection. Morantel did not affect the fecundity of adult O. ostertagi surviving treatment 18 days after infection which had similar average numbers of eggs in their uteri (range 13.4 +/- 0.73-16.8 +/- 0.98) as did parasites from control animals (range 12.0 +/- 0.70-13.6 +/- 0.66). Morantel could be detected at a concentration of 96 +/- 4.5 micrograms/g (dry weight) in the faeces of a calf 24 h after treatment with 10 mg/kg bodyweight of morantel tartrate. The concentration of morantel in replicate samples of this faeces exposed to natural atmosphere, but not to soil or soil organisms, declined slowly over the following 322 days. At day 322 after the start of the experiment 8.8 micrograms/g of morantel could be measured in the remaining faecal material. Throughout the faecal degradation study the concentration of morantel in the crusts of the replicate sample pats was lower than the concentration in the core samples.

Morantel tartrate release from a long-acting intraruminal device in cattle: pharmacokinetics and gastrointestinal distribution.

The pharmacokinetics and gastrointestinal distribution of morantel tartrate release from a sustained release trilaminate bolus in cattle were investigated over a 98-day period post-treatment. Six Holstein calves (125-150 kg) had permanent indwelling fistulae surgically inserted into the rumen, abomasum and terminal ileum. Samples of jugular blood, feces and ruminal, abomasal and ileal fluids were taken on days -3, 1, 4, 7, 10, 14 and weekly up to 98 days post-bolus administration. Morantel tartrate concentrations were measured by HPLC after extraction and clean-up. Morantel was not detected in plasma at any time after bolus administration. High concentrations of morantel tartrate were found in ruminal, abomasal and ileal fluids and feces over 98 days post-treatment. The morantel peak concentration (Cmax) was achieved at Day 1 post-administration in each of these compartments. The steady-state morantel concentration (Css) was achieved at approximately 10 days post-treatment and maintained for 91-98 days post-treatment in these gastrointestinal compartments. The morantel Cmax, Css, area under the zero (AUC) and first moment (AUMC) of the concentration-time curve were significantly higher (P less than 0.01) in feces than in other compartments. The in vivo drug release profile of this device has been determined. Steady-state concentrations for from 91 to 98 days have been confirmed.

A new anthelmintic ussay using rats infected with Trichostrongylus colubriformis

A new anthelmintic assay is described which uses immunosuppressed (60 ppm hydrocortisone acetate in diet) rats infected with the nematode Trichostrongylus colubriformis. Immunosuppressed rats were infected with 1500 T. colubriformis larvae, treated either orally or subcutaneously on Day 14 post-infection and necropsied 4 days after treatment. The worm counts in immunosuppressed control animals averaged 775 worms per rat. A range of benzimidazoles, levamisole hydrochloride, morantel tartrate, 22,23-dihydroavermectin B1a and α-milbemycin have been evaluated in the assay. The ED 95 values obtained indicate that rats infected with T. colubriformis provide a highly predictive model for assaying the activity of experimental drugs in vivo prior to studies in ruminants.

Continued susceptibility of Ostertagia ostertagi infective larvae to morantel tartrate

Continued susceptibility of Ostertagia ostertagi infective larvae to morantel tartrate

Further studies with a strain of Ostertagia ostertagi resistant to morantel tartrate

Borgsteede F. H. M. 1991. Further studies with a strain of Ostertagia ostertagi resistant to morantel tartrate. International Journal for Parasitology 21: 867–870. Two experiments with a morantel resistant strain of Ostertagia ostertagi were carried out. In the first experiment five groups of five calves were infected with 60,000 larvae of this resistant strain. Calves of one group remained untreated, calves of the other groups were treated with morantel tartrate, oxfendazole, levamisole or ivermectin in the recommended doses. It was demonstrated that there was side resistance to levamisole, but not to oxfendazole or ivermectin. Compared with the untreated controls the reduction percentages of the worm burdens were 45.3 (morantel tartrate), 99.7 (oxfendazole), 83.5 (levamisole) and 100 (ivermectin). In the second experiment a comparison was made between the effect of levamisole against a morantel susceptible strain of O. ostertagi and the resistant strain. Two groups of five calves were infected with the susceptible strain and two groups with the resistant one. One group of each pair remained untreated, the other was treated with levamisole. The reduction percentages of the worm burdens were 99.6 (susceptible strain) and 63.6 (resistant strain). This result confirms the efficacy of levamisole to susceptible O. ostertagi and the side resistance of the morantel resistant strain.

Performance and Internal Parasite Burden of Stocker Steers Treated Continuously with Morantel Tartrate

Three experiments were conducted to evaluate performance and fecal nematode egg counts in grazing stocker cattle receiving morantel tartrate (MT) in two continuously administered forms. In Exp. 1, 80 crossbred steers either received no anthelmintic (C) or were dewormed at the initiation of a 140-d bermudagrass grazing study with either levamisole injection (L) or MT in a sustained-release trilaminate (MSRT). Anthelmintics did not affect performance parameters, but fecal nematode egg counts were lowest from L, intermediate from MSRT, and highest from C at the end of the study. In Exp. 2, 60 crossbred steers grazing fall-regrowth smooth bromegrass were offered a mineral mixture of trace-mineralized salt and dicalcium phosphate (3:1 ratio) with 0 or 10% dried molasses and 0 or 5.58 mg/g MT. Steer gains were similar (P>.10) across treatments, but fecal egg counts were reduced (P<.05) by MT. In Exp. 3, 120 crossbred steers grazing smooth bromegrass pastures were used in an experiment with a 2 x 2 factorial arrangement of treatments to evaluate the effects of grazing intensity and 5.58 mg/g MT in a mineral mixture. Steers grazing at the highest stocking rate (3.7 steers/ha) had reduced (P<.01) gains but improved (P<.01) gain/ha compared with those grazing at the lower rate (2.5 steers/ha). Morantel tartrate reduced (P<.01) fecal nematode egg counts but had no effect on animal performance at either stocking rate. Morantel tartrate was effective in reducing fecal egg counts, but parasite burden in control animals in all three experiments was not sufficient to reduce animal performance.

A basis to extend the proof of migration routes of immature parasites inside hosts: estimated time of arrival of Nippostrongylus brasiliensis and Strongyloides ratti in the gut of the rat

The time taken for larvae of Nippostrongylus brasiliensis and a homogonic strain of Strongyloides ratti to complete their migration from the skin surface to the small intestine of the rat was estimated by a new method in which a mirror image of arrival times was created by counting mature parasites at day 8 (N. brasiliensis) or day 5 (S. ratti) in the intestines of rats that had received a single pulse of morantel tartrate by stomach tube at different times starting 10 h after skin application of exact doses of infective larvae. It was confirmed that the effect of the drug was confined to parasites in the gut, so that the kinetics of migration were unperturbed. The persistence of the anthelmintic effect in the gut was shown by independent assays to be less than 8 h for both species. The time-course of arrival calculated from drug pulse data corrected for persistent effects was compared with direct counts of larvae arriving in the intestines of rats not dosed with anthelmintic. Both methods agreed in all respects for N. brasiliensis, whereas the estimates for direct counts of S. ratti, lagged 15-17 h behind those from drug-treated rats. In the discussion it is argued that the anthelmintic method provides a more correct picture for S. ratti and, on this basis, rates and synchrony of migration of the two species are compared. The role of these data as part of a proof of migration routes is explained.

Efficacy of the morantel sustained release trilaminate matrix against gastrointestinal nematodes in beef calves

The effectiveness of the morantel sustained release trilaminate (MSRT) in controlling gastrointestinal nematodes through a grazing season was evaluated using 60 yearling beef stocker calves randomly divided into 2 groups of 30 animals each. In April 1985, the calves comprising the treatment group each received an MSRT designed to release morantel tartrate continuously for 90 days while those of the control group remained unmediated. All animals were weighed and samples of rectal feces were taken at 14-day intervals, beginning on Day 0, until trial termination (Day 168). At trial termination, 10 control and 10 treated calves were necropsied for recovery of gastrointestinal nematodes. Three sets of parasite-naïve tracer calves were utilized to evaluate the initial, interim and final levels of pasture contamination by nematode larvae. Overall, the use of the MSRT resulted in a 75.5% reduction ( P<0.001) in output of nematode eggs from the principals, an 81.8% reduction ( P<0.001) in numbers of gastrointestinal nematodes in principals (at trial termination), and a 96.9% reduction ( P<0.05) of pasture larval nematode contamination (as indirectly indicated by parasite burdens in tracer calves). The mean weight advantage of treated calves was 16.6 kg per head ( P<0.001).

Evaluation of the morantel sustained release trilaminate in the control of parasitic gastroenteritis in first season grazing cattle.

A novel intraruminal bolus developed for the sustained delivery of the anthelmintic morantel tartrate was evaluated in the seasonal control of parasitic gastroenteritis in first season grazing calves. The morantel sustained release trilaminate is a trilaminate sheet consisting of a central lamina of a morantel tartrate/ethylene vinyl acetate matrix coated on both sides with a thin impermeable layer of ethylene vinyl acetate. A symmetrical pattern of circular perforations punched through the device controls the release of morantel. Administration of the trilaminate to calves significantly reduced their faecal egg output compared with untreated controls and thus reduced pasture larval contamination. Clinical parasitic gastroenteritis was prevented in the treated calves and there were significant reductions in their worm burdens compared with the untreated control calves both during and at the end of the grazing season. The control of parasitic gastroenteritis resulted in a significantly greater (P less than 0.0001) weight gain, of 45 kg, by the treated calves.

Reliability and reproducibility of the larval paralysis test as an in vitro method for the detection of anthelmintic resistance of nematodes against levamisole and morantel tartrate

In order to study the reliability of the larval paralysis test as an in vitro for the detection of resistance of nematodes to levamisole and morantel tartrate, the influence of different parameters was evaluated using resistant and susceptible Ostertagia ostertagi strains. The operator, the sample (10% of the larvae present in the suspension), the incubation time (24, 48 or 72 h), the incubation temperature (20 or 25°C) and the observation period of the larvae (5 or 15 s) had no statistically significant influence on the test results. Statistical differences were obtained only when L 3 larvae of different ages (1 or 2 months) were used. Reversibility of the paralysis did not occur when concentrations of levamisole of ⩽200 μg ml −1 or morantel tartrate of <2000 μg ml −1 were used. The reproducibility of the test was fairly good, with a mean standard deviation of 21.3% for the LC 50 values. Morantel resistance in a strain of O. ostertagi was not confirmed as such by the larval paralysis test. The resistance factor was ⩽1, in spite of an efficacy of morantel of 77.4% as shown in vivo.