Evaluation of broad-spectrum anthelmintic activity in a novel assay against Haemonchus contortus, Trichostrongylus colubriformis and T. sigmodontis in the gerbil Meriones unguiculatus

The gerbil Meriones unguiculatus, infected with three species of nematodes, each located in a separate part of the gastrointestinal tract, provided a reliable laboratory assay for the evaluation of broad-spectrum anthelmintic activity. Gerbils harbouring 6-day-old infections of Haemonchus contortus, Trichostrongylus colubriformis and T. sigmodontis were given selected broad-spectrum anthelmintics by gavage. Three benzimidazoles, thiabendazole, oxfendazole and albendazole, a tetrahydropyrimidine, morantel, an imidazothiazole, levamisole hydrochloride, a macrocyclic lactone, ivermectin and an experimental natural product, paraherquamide, were active against all three nematodes at various dosages. Trichostrongylus colubriformis was most sensitive to levamisole hydrochloride, morantel, thiabendazole and paraherquamide whereas ivermectin, oxfendazole and albendazole were more effective against H. contortus. All compounds were active against the caecal nematode T. sigmodontis although it was less sensitive than T. colubriformis. Haemonchus contortus was more sensitive than T. sigmodontis to all anthelmintics tested except thiabendazole.

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.

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.

Efficacy of morantel sustained release trilaminate bolus against gastrointestinal nematodes in grazing dairy calves in Kenya

The efficacy of morantel sustained release trilaminate (MSRT) bolus against gastrointestinal nematodes was evaluated under field conditions over a 10-month period. Twenty weaner calves were randomly divided into 2 groups of 10 calves each and grazed from March to December on adjacent, similarly contaminated paddocks. Group 1 calves (T-1) served as untreated controls while group 2 calves (T-2) were dosed at turnout with MSRT bolus designed to release morantel tartrate continuously for 90 days. The efficacy of MSRT was assessed by comparison of parasitological data (faecal worm egg counts, herbage larval counts, worm counts from tracer calves and set-stocked trial calves, determination of haematological parameters and pepsinogen levels), weight gains and clinical status of the animals. Faecal egg counts from the treated group (T-2) were reduced by 100% (P < 0.001) following treatment and remained significantly (P < 0.05) lower than counts from T-1 calves up to trial termination. The use of MSRT bolus resulted in a reduction of 92% (P < 0.001) in the number of gastrointestinal nematodes in set-stocked calves at the end of the study and a 55 to 85.7% reduction in herbage larval infectivity as reflected in lowered parasite burdens in tracer calves. At the trial termination, the control calves had gained on average (+/- s.d.) 59.4 +/- 4.8 kg (200.0 +/- 7.4 g day-1) and the treated ones on an average 128.6 +/- 10.5 kg (530.0 +/- 13.1 g day-1).

Fumarate reductase: a target for therapeutic intervention against Helicobacter pylori

The potential of fumarate reductase as a therapeutic target against the human pathogen Helicobacter pylori was investigated by studying the cytotoxicity of morantel, oxantel, and thiabendazole, known to inhibit the enzyme in parasitic worms. Nuclear magnetic resonance spectroscopy was employed to investigate the effects of the inhibitors on the fumarate reductase activity of laboratory-adapted and wild-type bacterial strains. Production of succinate from fumarate in H. pylori cells was inhibited by morantel, oxantel, and thiabendazole. Cell growth and viability techniques were used to examine the bacteriostatic and bactericidal effects of the three anthelmintics. Each of the antiparasites arrested growth and produced cell death in liquid cultures, although the minimal inhibitory and bactericidal concentrations of these compounds are such that they would not be of therapeutic use. The strength of the effects as measured by minimal inhibitory and bactericidal concentrations was oxantel > thiabendazole > morantel. The findings suggested that fumarate reductase is an essential component of the metabolism of H. pylori and as such constitutes a possible target for therapeutic intervention in the treatment of the bacterium.

A comparison of early and mid grazing season suppressive anthelmintic treatments for first year grazing calves and their effects on natural and experimental infection during the second year

A comparison was made of the efficacy and parasitological sequelae over 2 years, of continuous and intermittent periods of anthelmintic suppression applied both early and in the middle of the first grazing season of calves. Five groups of 15 calves grazing separate paddocks within the same field were allotted to one of the following treatment regimes during their first year at grass: Group 1, untreated controls; Group 2, treated with ivermectin injections at 3, 8 and 13 weeks after turnout; Group 3, treated with ivermectin injections at 10, 15 and 20 weeks after turnout; Group 4, treated with a morantel slow release intraruminal bolus at turnout; Group 5, treated with a morantel slow release bolus at 10 weeks after turnout. Five animals from each group were slaughtered at the end of both grazing seasons. Two months after the end of the second season the remaining five calves were challenged with an experimental infection of 250,000 third-stage larvae (L3) of both Ostertagia ostertagi and Cooperia oncophora. All treatment regimes protected the respective calves from parasitic gastroenteritis. Over the 2 year observation period Groups 2 and 4 showed significantly better weight gain than other groups, and at the end of the first season, they were found to harbour significantly fewer O. ostertagi in the early fourth stage of development. During Year 1, Groups 2 and 3 excreted much lower percentages of Ostertagia spp. eggs than other groups. In Year 2, Group 2 excreted a higher percentage of Ostertagia spp. eggs although the total egg output was approximately half that of Group 1 during the same period. The results showed that the effects of anthelmintic suppression on egg output of different nematode species was affected by the activity of the anthelmintic used.

Overberg research projects. XVI. First-stage larval reduction test versus the controlled anthelmintic test to assess the efficacy of anthelmintics against nematode parasites of sheep

Results of a first-stage larval reduction test (L1RT) were compared with those of a controlled anthelmintic test (CAT) done on naturally infected sheep which grazed on spray-irrigated grass/legume pastures at Tygerhoek Experimental Farm near Riviersonderend in the southern Cape Province. The 3 anthelmintics used were morantel, ivermectin and levamisole. According to the L1RT, treatments reduced the geometric means of Strongyloides by 74.2 to 95.2% and those of the adults of all the other genera (Haemonchus, Nematodirus, Oesophagostomum, Teladorsagia, Trichostrongylus and Trichuris) by 99.4 to 99.75%. By contrast the results of the CAT were more variable, placing the reliability of the L1RT in doubt. In addition, the CAT could also evaluate the effect against fourth larval stage Teladorsagia.

Prophylaxis of bovine trichostrongylidosis in the alpine region: effect of pasture contamination on infections in calves receiving a morantel sustained-release trilaminate bolus in mid-July

In the alpine region, mixed grazing systems with cattle of different age, origin and prophylaxis against trichostrongylid infections are most common. Under these conditions the administration of anthelmintic devices to susceptible calves is frequently postponed to June or July to achieve a better protection during the period of increased pasture infectivity in summer and autumn. In a field experiment with 27 first-year grazing calves a morantel sustained-release trilaminate bolus (MSRT, Pfizer) was given to two groups (Groups A and B) of nine naturally infected calves each, on 22 July. Calves of Group B were moved to a clean pasture (B) 1 day later, whereas the calves of Group A remained on the previous pasture (A) together with nine untreated calves (Group C). The contamination with infective larvae (L3) on Pasture A remained below 1000 L3 kg-1 dry matter, which was sufficient to produce clinical parasitic gastroenteritis in five of nine control calves. The MSRT bolus reduced the mean egg output by more than 90% within 14 days after administration and prevented clinical parasitic gastroenteritis in the calves of Groups A and B. Owing to the persisting infection risk on Pasture A, the mean serum pepsinogen levels reached about 3000 mU tyrosine in the calves of Group A in September compared with approximately 2000 mU in Group B grazing the clean pasture. However, the differences in pasture contamination were not reflected in the mean bodyweight of the calves, which were 20 kg heavier at the end of the trial in both MSRT-treated groups compared with the control calves (P < 0.01). As there is a high probability that a moderate larval contamination is present on prealpine and alpine community pastures in summer, the metaphylactic use of an MSRT bolus in mid-July is likely to limit trichostrongylid infections within a subclinical range and thus provides sufficient protection of susceptible calves against parasitic gastroenteritis.

Activity of morantel citrate against strains of benzimidazole-resistant nematodes of sheep in the United Kingdom

The activity of morantel citrate (5.94 mg/kg base) was determined in laboratory tests against field isolates of benzimidazole-resistant nematodes. Its efficacies against adult and seven-day-old worms were 100 per cent and 100 per cent for Cooperia curticei, 95.1 per cent and 69.8 per cent for Haemonchus contortus and 100 per cent and 82 per cent for Ostertagia circumcincta. Morantel citrate was 100 per cent effective against benzimidazole-susceptible Nematodirus battus and Trichostrongylus vitrinus, and it reduced faecal egg counts by 97.9 per cent in sheep infected naturally with benzimidazole-resistant H contortus and O circumcincta.

Epidemiology of trichostrongylidosis in cattle: development of infective larvae in the second part of the grazing period and their contribution to infections in the same year

A grazing experiment was performed in the Swiss midland region with 22 first-season calves which were grazed together from May to mid July when they were allocated to two equal groups, one receiving a morantel sustained-release trilaminate bolus (Paratect Flex) bolus, Pfizer, Zurich, Switzerland) and the other one remaining as an untreated control. Each group was moved to a clean pasture on 21 July. The larval contamination on the pasture with the control animals reached 4652 third stage larvae (L3) per kilogram of dry matter (L3 kg-1 DM) after 10 weeks. Parasitic gastroenteritis was observed in two calves of the control group in August, and mean serum pepsinogen levels exceeded 4000 mU tyrosine in this group in September. Eggs from Ostertagia sp. and Cooperia sp. that were excreted by the animals at the beginning of July and the end of August showed similar hatching rates of 94% and 99%, respectively. In the calves of the bolus group the egg output was reduced by 95% within 14 days of administration of the bolus. Larval contamination on the pasture of the bolus group was zero until the beginning of September when a slight increase occurred, reaching 793 L3 kg-1 DM in October. At the end of the trial the bolus-treated calves had a mean weight gain advantage of 18 kg (P < 0.05) compared with the controls. The results confirm that a second generation of larvae developed on pasture in August and September and caused parasitic gastroenteritis in first-year grazing calves in late summer. The relevance of the results for the prophylaxis of parasitic gastroenteritis in calves in mixed grazing systems with calves and older cattle is discussed.

Sequential in vivo measurements of body composition of calves exposed to natural infection with gastrointestinal nematodes

Sequential in vivo measurements of total body water, exchangeable sodium and exchangeable potassium, made by radioisotopic dilution techniques, were used to determine changes in body composition in calves exposed to natural infections with gastrointestinal nematodes during their first grazing season. Two groups of calves were studied, one of which received a sustained release anthelmintic bolus at turn out. Over the grazing season the bolus-treated calves showed a significantly improved pattern of bodyweight gain, compared with the untreated control calves. There were also significant increases in both total body water and exchangeable potassium, as a percentage of the bodyweight, in the bolus calves compared with the controls. These findings indicated that body protein as a percentage of bodyweight was increased in the bolus animals. The bolus-treated calves also had significantly lower serum pepsinogen concentrations, faecal egg counts and worm burdens.

Efficacy of the morantel sustained release trilaminate bolus against gastrointestinal nematodes and its influence on immunity in calves

An experiment was conducted in calves to investigate the efficacy of a morantel sustained release trilaminate bolus (MSRT) to control gastrointestinal parasitism and to assess the development of immunity during the use of MSRT. Two groups (M and U) of four calves each were infected three times a week with a mixed Ostertagia ostertagi and Cooperia oncophora infection for 12 weeks. Calves of Group M received an MSRT at the start of the experiment. Twenty weeks after the start of the experiment, all animals, including a previously uninfected control group (C), received a challenge with 100,000 Ostertagia and 100,000 Cooperia. After a further 4 weeks all calves were necropsied for worm counts. During the trial calves were weighed and faecal egg counts, larval differentiation and pepsinogen concentrations were determined. The results demonstrated the high level of efficacy of the MSRT in reducing the faecal egg output and preventing parasitic gastroenteritis under conditions of a continuous high rate of infection. Efficacy of treatment was higher for Cooperia than for Ostertagia. Post-mortem worm counts suggested a partially impaired immunity build-up in Group M, at least for Cooperia.

A new anthelmintic assay 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 alpha-milbemycin have been evaluated in the assay. The ED95 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.

Effect of sustained release and pulse release anthelmintic intraruminal devices on development of pathophysiological changes and parasite populations in calves infected with Ostertagia ostertagi and Cooperia oncophora

An experiment was conducted in calves to investigate the effect of sustained release and pulse release anthelmintic intraruminal boli on the development of pathophysiological changes following daily infection with Ostertagia ostertagi and Cooperia oncophora for six weeks. After infection various pathophysiological changes were detected including increases in serum pepsinogen concentration, enteric plasma protein losses and in the catabolic rate of albumin. Such changes developed rapidly in the unprotected calves following patency after 17 days and persisted until the termination of the study. There were indications that the sustained anthelmintic release device was more efficacious than the pulse anthelmintic release device in reducing the worm burdens and early pathophysiological changes associated with infection. It was found at necropsy that the release of anthelmintic by the oxfendazole pulse release bolus had been delayed in several calves.

Strategic use of anthelmintics to prevent parasitic gastroenteritis in cow-calf herds in California

On the basis of the hypothesis that the peak numbers of infective nematode third-stage larvae (L3) on herbage in winter months results from fall contamination of pastures, 2 methods to reduce fall contamination were tested. In trial 1, morantal sustained-release boluses were administered to 15 fall-calving cows on Sept 7, 1982. Fifteen untreated cows (controls) were placed on separate pastures. Numbers of L3 on herbage during the winter and spring were assessed by use of worm-free tracer calves. In trial 2, 19 cattle due to calve in the fall were administered 200 micrograms of invermectin/kg of body weight, SC, on Sept 2, 1983. Also, 17 cattle similarly were given a placebo injection and served as control animals. Treated cattle were placed on the pasture used by control cattle in trial 1 and control cattle on the pasture used by treated cattle in trial 1. Worm-free tracer calves were again used to assess numbers of L3 on herbage. In trial 1, tracer calves grazing the control animal pasture from January 14 to 28 acquired 37 times as many nematodes as did those grazing the treated animal pasture. In trial 2, the greatest difference observed was a 10-fold increase of nematodes in calves grazing control animal pastures, compared with worm numbers in tracer calves grazing the treated animal pasture.

A field strain of Trichostrongylus colubriformis resistant to levamisole and morantel in South Africa

A strain of Trichostrongylus colubriformis from Nottingham Road, in Natal, was found to be solidly resistant to levamisole and morantel at the recommended dose levels. Untreated control sheep in fact harboured fewer worms at slaughter than either of the 2 treated groups. In contrast, the benzimidazoles and ivermectin were more than 99.9% effective against this worm strain. The possible implications of escalating resistance to anthelmintics in the gastrointestinal nematodes of sheep are discussed.

South African field strains of Haemonchus contortus resistant to the levamisole/morantel group of anthelmintics

A strain of Haemonchus contortus from the Pietermaritzburg district of Natal was found to be resistant to levamisole (geometric mean efficacy 76.5%), morantel (41.9%), the benzimidazoles (oxfendazole: 33.7%) and rafoxanide (82.0%), but apparently fully susceptible to closantel and disophenol. In the case of ivermectin, a mean of 5.2% of the H. contortus was not removed at a dosage of 200 micrograms kg-1 live mass. A second strain of H. contortus, from Amsterdam in the south-eastern Transvaal, showed reduced susceptibility to levamisole (80.8%) and morantel (46.2%), the only 2 drugs tested. This is apparently the first report of resistance to the levamisole/morantel group of anthelmintics in sheep in South Africa.

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 unmedicated. 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 less than 0.001) in output of nematode eggs from the principals, an 81.8% reduction (P less than 0.001) in numbers of gastrointestinal nematodes in principals (at trial termination), and a 96.9% reduction (P less than 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 less than 0.001).

Efficacy of a novel sustained release anthelmintic device in preventing parasitic gastroenteritis in first-season calves

The efficacy of the first of a new generation of intraruminal devices for cattle, the morantel sustained release trilaminate, was assessed in two field trials. In each trial the animals were divided into a control group and a treated group. The device was administered to each calf before turn out in the spring and the reduction of gastrointestinal parasitism resulted in a substantial reduction in the level of pasture contamination with infective helminth larvae later in the season. Compared with the control calves the treated calves had a 94 per cent reduction of worm burdens acquired over the entire grazing season in the first trial, despite the controls being treated for clinical disease in September. In the second trial four anthelmintic treatments were administered to the control calves during the grazing season, but nevertheless a 64 per cent reduction of worm burdens in the treated group compared to the control group was recorded. The control of parasitic infection by the sustained-release devices resulted in mean weight gain advantages of 28.3 kg and 34.7 kg by the treated animals in the first and second trials respectively.

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.

Comparison of two early season anthelmintic programmes on a commercial beef farm

Two early season suppressive anthelmintic programmes, ivermectin given three, eight and 13 weeks after turn out and a morantel sustained release bolus administered at turn out, were compared on a commercial farm. The morantel treated cattle grew significantly faster than the ivermectin treated group during the period of treatment, on average at 0.80 kg/day compared with 0.71 kg/day (P less than 0.01). In the second half of the grazing season (13 to 25 weeks after turn out) the ivermectin treated group grew faster than the morantel treated group although the difference was not statistically significant. Over the entire grazing season there was no significant difference in average growth rate between the morantel treated group which grew at 0.80 kg/day and the ivermectin treated group which grew at 0.77 kg/day. These results were related to pasture larval counts, faecal egg counts and plasma pepsinogen levels throughout the grazing period. It was concluded that the morantel sustained release bolus allowed growing cattle to reach their production potential during the period of treatment. However, its efficacy in maintaining production throughout the grazing season was reduced by the 90 day treatment period which failed to give the level of control of gastrointestinal nematode parasites achieved by the 105 day period of treatment in the ivermectin programme.

Efficacy of morantel sustained-release bolus in control of gastrointestinal nematodes of weaned calves during the autumn-winter grazing season

A 168-day study was conducted to evaluate the efficacy of morantel tartrate sustained-release bolus (MSRB) in controlling gastrointestinal parasitism in weaned calves during autumn-winter grazing in the temperature climate of southern United States. Sixty-two weanling Angus heifers were used to assess treatment differences. Six sentinel heifers were necropsied to assess pretrial gastrointestinal worm counts. The remaining 56 heifers were assigned to 4 groups of 14 heifers each and were placed on four 4.86-hectare dormant Bermuda grass pastures (1 group/pasture) that had been no-till interseeded with cereal rye in early October. Heifers in 2 groups were given 1 MSRB in early November; the other 2 groups served as nonmedicated controls. Three heifers (principals) from each of the 4 groups were necropsied on posttreatment days 57, 112, and 168 (end of study) for total worm recovery. Eight 5-month-old tracer steers, raised worm-free from birth, grazed the 4 pastures (2/pastures) for the first 21 days of the study and then were kept in drylot for 21 days before being necropsied. Level of larval contamination of pastures grazed by control and MSRB-treated heifers were comparable, because the mean number of nematodes recovered from tracer steers grazing the control and MSRB pastures were 47,449 and 53,835, respectively. At 28 days after treatment, MSRB-treated heifers had lower (P less than 0.05) mean egg counts/g of feces than did control heifers (280 vs 13).(ABSTRACT TRUNCATED AT 250 WORDS)

Strategic use of anthelmintics for parasitic nematodes in cattle and sheep

Treatment regimes for the control of parasitic nematodes in cattle and sheep are reviewed. The advantages and disadvantages of each strategy are outlined and the veterinarian's judgement of the management and economic constraints involved when recommending a particular system to a client is emphasised.

Use of the sustained-release morantel bolus in stocker calves in southern United States

Two groups of 21 mixed-breed heifers were wintered on separate permanent pastures. Each heifer from one group was administered a sustained-release morantel bolus on October 7 (day 0), and the other group remained as untreated controls. Body weights were determined and fecal samples were taken at 28-day intervals. At the onset of the trail and at every 56 days, 6 heifers were removed from each group for slaughter to determine the developmental stages and the number of gastrointestinal nematodes. In addition, 3 tracer calves that were free of gastrointestinal nematodes were released on each pasture for 28 days at the beginning of the trail and after the last experimental-group calves had been removed. The 6 calves slaughtered on day 0 of the trail had a mean of 5,544 gastrointestinal nematodes. Tracer calves released on day 0 and removed on day 28 of the trial acquired 31,143 and 30,530 gastrointestinal nematodes from the pastures containing the treated and control heifers, respectively. Throughout the trial, the number of nematodes in the control calves increased at each sampling date (mean, 126,168 worms), whereas the mean number of worms in the treated heifers was 45,458. Tracer calves placed in the pastures after the 168-day trail acquired significantly more worms (9,632 vs 2,899; P less than 0.05) from grazing the pastures with control heifers than from grazing the pastures with treated heifers. Counts of eggs per gram of feces were significantly different (P less than 0.01) between the 2 groups from day 28 through day 112.(ABSTRACT TRUNCATED AT 250 WORDS)

Control of gastrointestinal parasitism with an oxfendazole pulse-release anthelmintic device

The efficacy of a pulse-release oxfendazole bolus (OPRB) against gastrointestinal nematodes was evaluated under field conditions and compared with a sustained release morantel bolus (MSRB). Three groups of 10 calves were grazed from May to September on adjacent, similarly contaminated 3-acre paddocks. One group was dosed at turnout with the OPRB, the second group with the MSRB and the third group left as nontreated controls. Pasture larval counts peaked at greater than 60,000 larvae/kg dry weight of herbage in September on the control paddock, associated with a mean egg count of 1040 eggs/g faeces and clinical symptoms. A low rise in larval counts occurred on the MSRB plot, and also low helminth egg counts. On the OPRB plot, pasture larvae and faecal egg counts were recorded only intermittently; the September egg counts were only 3.5% of those of the controls; serum pepsinogen data showed a similar picture. At the end of the experiment, the OPRB calves had a mean weight advantage of 40 kg over the controls, and 12 kg over the MSRB group. Feed intakes were highest in the OPRB group in July and September.

A field evaluation of benzimidazole and nonbenzimidazole drugs in a herd of dairy goats

A study was conducted to investigate the efficacy of six anthelmintics in a herd of dairy goats. Pretreatment larval cultures indicated that the goats were infected with Haemonchus contortus and Trichostrongylus colubriformis. Three separate treatment regimens were administered. In each trial, mature nonlactating goats were allocated into two treatment groups and a control group. Treatment groups received thiabendazole (TBZ) or levamisole (LEV), mebendazole (MBZ) or fenbendazole (FBZ), and morantel tartrate (MOR) or ivermectin (IVR). LEV, MOR, and IVR reduced fecal strongyle egg counts by 99% to 100% of pretreatment values. The benzimidazole (BZD) drugs changed pretreatment fecal egg counts by +2% to -32%. Results of posttreatment larval culture demonstrated the presence of H contortus larvae following the administration of BZD drugs.

Feed intake of grazing calves exposed to trichostrongyle infection and treated with the morantel sustained release bolus

Herbage intake was measured in two groups of 20 first-year grazing cattle. The animals in one group each received a morantel sustained release bolus at turnout to control nematode parasitism and the animals in the other group remained untreated. The latter group showed a mean peak faecal egg count of 655 eggs per gram (e.p.g.) in October associated with high serum pepsinogen concentration and clinical signs of ostertagiasis, compared with a peak of 119 e.p.g. in the treated group which remained in good health. In September the daily voluntary feed intake of the untreated animals was significantly depressed (94 g kg-1 body weight vs. 77 g kg-1 P less than 0.001), but no difference in digestive efficiency was recorded between the two groups. This difference in feed intake was associated with a 47 kg mean live weight advantage of the treated animals at housing.

Larvicidal properties against Ostertagia ostertagi of the faeces of calves treated with a sustained release formulation of morantel tartrate

An experiment was carried out to assess the effect of morantel tartrate in the faeces of calves treated with a bolus on the survival and development of Ostertagia ostertagi eggs. Since the drug delivered from the bolus greatly reduces the nematode population in an infected animal and thus the number of eggs excreted it was necessary to mix O ostertagi eggs into the faeces of calves to which boluses had been administered. In three preliminary experiments it was shown that the methods used to extract the nematode eggs from faeces of infected cattle and remix them into faeces from uninfected cattle did not appear to affect their development into larvae or their even distribution in the faeces into which they had been remixed. The concentration of morantel tartrate lethal to O ostertagi eggs was in the range 0.0015 to 0.0025 M in vitro. It was demonstrated that the presence of the drug in the faeces of dosed calves prevented the maturation of approximately 99 per cent of O ostertagi eggs to infective larvae between days 7 and 84 after the administration of a bolus and of 75 per cent on day 91. These results help to explain the well recognised effect of the bolus in cleaning pastures of O ostertagi.

Efficacy of the morantel sustained-release bolus in grazing cattle in North America

The efficacy of using a bolus containing morantel in a sustained-release preparation for controlling naturally acquired gastrointestinal parasitic infections in weaned calves and yearling cattle was investigated during the 1982 grazing season at selected sites in the United States and Canada. According to a common trial design under various climatic and management conditions, 10 field trials were conducted with the bolus. At the time of spring turnout, a bolus was administered to each calf or yearling in the treated group. Then, treated and control cattle grazed separate but equal areas of divided pasture(s). The epidemiologic pattern of parasitic gastroenteritis in control animals and the effect of treatment on this pattern was determined in each trial. Safety and practicality of use of the bolus also were established. When compared with untreated cattle (control), those given the bolus deposited significantly (P less than 0.05) fewer worm eggs (89% reduction) during the first 90 days of the grazing season, as well as significantly fewer (P less than 0.05) worm eggs (84% reduction) during the entire grazing season. Consequently, during the second half of the grazing season, larval populations on treated pastures remained significantly (P less than 0.05) lower (66% reduction), compared with numbers of larvae found on control pastures. For pastures grazed by treated and control cattle at trial initiation, mean worm counts recovered from tracer calves were equal, indicating comparable pasture contamination at the beginning of the grazing season.(ABSTRACT TRUNCATED AT 250 WORDS)

A survey by questionnaire of parasitic worm control in cattle and sheep at the Glasgow University Lanark practice

The results of a questionnaire circulated in 1984 concerning parasitic worm control on cattle and sheep farms in a veterinary practice in the west of Scotland are reported. Control by grazing management or anthelmintic treatment was used in 92 per cent of the cattle herds and in all the sheep flocks. The use of anthelmintic drugs was greatest on farms where grazing control was also practised. Benzimidazoles were the most frequently used anthelmintic drugs.

Autumn acquisition of nematodes by calves given a morantel sustained-release bolus the preceding spring

Reinfection with nematodes late in the grazing season was assessed in calves treated the preceding spring with a morantel sustained-release bolus (MSRB). During an initial 155-day grazing period, MSRB-treated calves (n = 15) grazed a pasture used the preceding year for identically treated calves (MSRB pasture). Control calves (n = 15) were not given anthelmintic treatment in the spring and grazed heavily contaminated herbage for the initial 155-day period (control pasture). At the end of the initial grazing period, 3 calves from each group were killed for parasite recovery and counting, with control calves found to harbor 9.2 times more nematodes, compared with the MSRB-treated calves. Nematode counts from tracers killed periodically during the initial grazing period were of similar proportions, reflecting the much greater nematode exposure experienced by the control calves, compared with the MSRB-treated calves. At the end of the initial grazing period, 10 calves (5/group) were placed on a common, contaminated pasture after all were treated twice with fenbendazole (10 mg/kg of body weight, 7 days apart) while on concrete. The second grazing period was for 29 days, followed by a 3-day confinement on concrete. Then, the calves were killed and necropsied. During the 29-day grazing period, the MSRB-treated calves maintained their weight advantage over the control calves, and significant differences in nematode egg counts were not found between the 2 groups of calves. At necropsy, the MSRB-treated calves harbored 27.9% fewer nematodes than did the controls, indicating that prior therapeutic and prophylactic anthelmintic activities of the MSRB did not predispose the animals to enhanced acquisition of nematodes after MSRB protection.

Effects of cholinergic drugs on muscle contraction in Moniliformis moniliformis (Acanthocephala)

In whole Moniliformis moniliformis spontaneous muscle contractions were rhythmic; longitudinal contractions were measured with a force transducer. The cholinergic agonists levamisole and nicotine significantly increased muscle tension in whole worms; these contractions were tonic and were antagonised by the ganglionic blocker pentolinium and by piperazine. In addition, levamisole-induced contractions were inhibited by gallamine, hexamethonium, and norepinephrine. In worm segments, where drugs in solution were injected through the worms, acetylcholine (ACh) and nicotinic agonists were effective in causing contractions, whereas muscarinic agonists in concentrations up to 1 mM had no effect. Although muscle contraction in M. moniliformis was induced by nicotinic agonists, these contractions were effectively antagonised by a range of chemicals that block ganglionic, skeletal, and muscarinic sites in vertebrates. The presence of ACh in M. moniliformis and the effects of nicotinic agonists on muscle contraction suggest that ACh is a putative excitatory neurotransmitter.

Control of gastrointestinal parasitism in calves in Sweden over six years using the morantel sustained release bolus

During the 6 years 1979-1984, the use of the morantel sustained release bolus (MSRB) was monitored in first year grazing calves. Twenty-four to 30 calves each year were allotted to two groups (controls and MSRB-treated) and turned out at the end of May on the same pasture divided into two equal areas. After housing in October, each group was kept in boxes and fed concentrates, whey and hay. The calves were weighed at monthly intervals until the first animals were sent to slaughter. No cases of clinical ostertagiasis Type I were observed in the control calves during the grazing seasons, but in one year (1983) clinical signs occurred 2 weeks after housing. The number of overwintering larvae was influenced by pasture contamination the previous season and climatic conditions during winter and spring. The fecal egg output of the control animals during the grazing season did not reflect the level of pasture contamination at turnout. The build-up of pasture larval contamination during the later part of the grazing season was influenced by the climatic conditions. The fecal egg output of the treated calves was low during the entire grazing season resulting in a significantly reduced pasture contamination. A significantly reduced live-weight gain in the control calves was demonstrated at housing in five of the six years. When heavily infected at housing, the performance of the control calves was still influenced negatively during the fattening period indoors.

A comparison of nematode control programs for cattle in south western Victoria

Nematodiasis and its subsequent effect on production in Hereford weaner steers in western Victoria was studied during 1983 and 1984. In the first summer, steers were allocated to 2 replicates of 6 treatments--No treatment (Nil); Morantel slow release bolus in March (M1); Morantel bolus in March and June (M2); pour-on levamisole in January, May and July (R3); albendazole in January and July (V2) and albendazole in January, May and July, (V3). In 1984, treatment M2 was discontinued to provide extra replicates for Nil and M1. The replicate paddocks were 5 ha and were stocked with 7 and 8 steers in 1983 and 1984, respectively. Nematode egg counts in faeces, were generally less than 50 epg, indicating low numbers of adult nematodes. Faecal egg counts were highest in autumn and declined during the year. There was a significant (P = 0.02) effect of treatment on mean faecal egg count. Mean egg counts for treatment groups Nil and M1 were 16 and 10 epg above the overall mean (47 epg); those of the other treatments were 6 to 12 epg below the mean. There were no significant (P = 0.8) differences between treatments in the numbers of nematode larvae on pasture, during the experiment. At the end of both years of the experiment most nematodes (92%) were early fourth stage larvae of O. ostertagi. There were no consistent differences in nematode counts between treatments. There were no significant (P = 0.33) differences between treatments in bodyweights at any time during the experiment.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy of a morantel sustained-release bolus for control of gastrointestinal parasites in winter-grazed steers in Mississippi

From Nov 22, 1983 through May 15, 1984, 36 crossbred steers were allotted into 3 treatment groups (12/group) and were grazed on separate 3.4-hectare pastures. On Nov 22, 1983, the steers were administered a single morantel sustained-release bolus (MSRB), orally (group 1), or a single dose of thiabendazole (TBZ; 66 mg/kg of body weight, orally; group 2), or were left untreated (group 3; controls). Animal weights, nematode egg counts in fecal specimens, and plasma pepsinogen concentrations were monitored monthly. At the termination of the study, 4 steers from each treatment group were slaughtered and necropsied and worm counts were determined. A set of parasite-free tracer calves (3/treatment group) were grazed with each treatment group for 1 month, beginning on Nov 22, 1983; a second set of tracer calves (3/group) were grazed with each treatment group for 1 month, beginning Apr 3, 1984. At the end of their respective grazing periods, tracer calves were held for 3 weeks and then were slaughtered and necropsied and their worm counts were determined. Mean nematode egg counts in fecal specimens of group 1 (MSRB treated) were significantly lower (P less than 0.05) than that of the TBZ-treated or nontreated steers. Differences in worm counts were not found between treatment groups. Differences in worm counts of tracer calves were not found among the 3 groups for November 1983 nor for April 1984. Steers treated with the MSRB had a higher mean weight gain (P less than 0.06) than did the control or TBZ-treated steers.

Field evaluation of the oxfendazole pulse release bolus for the chemoprophylaxis of bovine parasitic gastroenteritis: a comparison with three other control strategies

Three trials were conducted in southern England involving 120 autumn-born calves to evaluate the ability of an oxfendazole pulse-release intraruminal device (OPRB) to control parasitic gastroenteritis (PGE). Matched groups were set-stocked on adjacent paddocks. One group received an OPRB at turn-out; one was treated with an alternative chemoprophylactic programme; while the third acted as an untreated control. In each trial clinical PGE occurred in the latter group but not in OPRB or alternative strategy groups. The OPRB, the morantel sustained release bolus (MSRB) and fenbendazole administered at 3 and 6 weeks after turn-out gave similar weight-gain benefits when compared with untreated controls (P less than 0.01), but the growth rate of animals given regular levamisole treatments from July to housing was significantly poorer than the matching OPRB group (P less than 0.05) although better than controls. Faecal egg-output of OPRB calves was reduced by 97.0-99.9% compared with 95.5 and 58.9% for MSRB and fenbendazole treatments. Consequently, the late summer/autumn peaks in pasture larval counts were considerably reduced in all treatment groups other than the late-season levamisole strategy which reduced overall egg-output by only 37.6%. Serum pepsinogen and gastrin values confirmed a greater degree of abomasal disturbance in calves grazing on the more highly contaminated pastures. Incidental lungworm infections became clinically apparent in the control groups of two trials but not in any OPRB or alternative treatment group.

Efficacy of morantel sustained release bolus against gastrointestinal nematodes in first season grazing Holstein calves

The efficacy of the morantel sustained release bolus (MSRB) in reducing gastrointestinal parasitism in first season grazing calves was evaluated during the summer--autumn grazing seasons of 1982 and 1983 in western Oregon. Each of 38 calves (1982) and 40 calves (1983) were randomly assigned to either control or treatment groups which were given MSRB on the day of turnout onto pasture. Mean worm burdens from tracer calves grazed with treated animals in 1982 and 1983 showed overall reductions of 86.4% (P greater than 0.05) and 84.3% (P less than 0.01), respectively, compared to tracers grazed with controls. Ostertagia ostertagi, Cooperia oncophora and Nematodirus helvetianus were the primary nematodes collected at necropsy. Twelve full-season 1982 tracer animals (6 treated and 6 control) indicated an 88.1% (P less than 0.05) overall reduction in mean worm burdens. Mean fecal worm egg per gram (EPG) counts of treated animals reflected a reduction of 69% (P less than 0.05) in 1982 and 90% (P less than 0.05) in 1983. Autumn inhibition of O. ostertagi was observed. In the 1982 trial the control animals showed a slight mean weight gain advantage over the treated group from Day 84 until Day 160 (trial termination) when the mean difference was 7.9 kg. The final mean weight gain advantage of treated animals in 1983 was 13.5 kg (P less than 0.05). These trials demonstrated that the MSRB was an effective anthelmintic for reducing gastrointestinal parasitism in grazing calves and for decreasing pasture larval contamination.

Efficacy of a morantel sustained-release bolus for the control of gastrointestinal nematodes in Florida dairy heifers

The effectiveness of a morantel sustained-release bolus (MSRB) in controlling gastrointestinal nematode infections was determined in 70 Holstein heifer calves with no prior grazing experience. Calves were allotted to 2 treatment groups and were maintained in Florida during the grazing season on divided pastures of equal area. One MSRB was administered to each calf in 1 group at the time of turnout onto spring pasture, whereas calves in the other group remained as nonmedicated controls. By the end of the grazing season, treatment resulted in significantly (P less than 0.05) lower worm burdens and significantly improved weight gains. The MSRB-treated calves were able to reach breeding weight 2 to 4 weeks earlier than did nonmedicated calves.

Resistance of Trichostrongylus colubriformis to levamisole and morantel: differences in relation to selection history

Two field strains of Trichostrongylus colubriformis were tested by in vitro and in vivo methods for resistance to morantel, levamisole and thiabendazole and compared with an anthelmintic-naive laboratory-passaged strain (McM). One field strain (TAS) was isolated from a dairy goat herd which had experienced severe helminthiasis despite intensive anthelmintic usage. The other (BCK) was isolated from sheep which had been treated solely with levamisole over a 6-year period. The BCK strain had very high levels of both levamisole and morantel resistance. In contrast the TAS strain was resistant to morantel but highly susceptible to levamisole. This finding is contrary to the expectation that selection with morantel automatically confers resistance to levamisole, the converse of which was shown to apply in the BCK strain. Although the TAS strain was exposed to levamisole prior to isolation, examination of the drug's pharmacokinetics in goats indicated that it exerted little if any anthelmintic effect, and therefore selection pressure, on the parasite population. This study suggests that the mechanism of levamisole resistance covers a wide spectrum, and embraces that for morantel. It also suggests that in order to conserve the effectiveness of the levamisole/morantel group of broad spectrum anthelmintics, morantel should be used to the exclusion of levamisole until resistance is detected, at which time levamisole may be introduced to re-establish high levels of control.

Efficacy of repeated doses of levamisole, morantel, fenbendazole, and ivermectin against gastrointestinal nematodes in ewes

Levamisole, morantel, fenbendazole, or ivermectin was administered at 2-week intervals from May 1 through Sept 14, 1985, to breeding ewes (20 ewes/drug) infected with various gastrointestinal nematodes. All ewes had fewer gastrointestinal nematode eggs per gram of feces (epg) after 2 treatments, compared with pretreatment epg counts. Ewes administered ivermectin continued to have a low mean epg (0 to 3) throughout the study. The mean epg counts of ewes treated with levamisole increased from 3 to 483 during the study. This increase was similar to that of ewes treated with morantel (7 to 485 epg). The mean epg count of fenbendazole-treated ewes increased from 4 to 192 during the study. By the end of the study, the mean epg counts when expressed as a percentage of the pretreatment epg counts were 4% (ivermectin), 249% (fenbendazole), 627% (levamisole), and 630% (morantel). With the exception of the ivermectin-treated ewes, the epg count increased almost linearly in the ewes after the 2nd anthelmintic treatment. These data indicate that the gastrointestinal nematodes (including Haemonchus contortus) may have developed more resistance to levamisole and morantel than to fenbendazole. On the basis of the epg counts, resistance to ivermectin did not develop during the 4.5-month treatment period. The percentage of ewes shedding eggs after 2, 4, and 6 anthelmintic treatments was lowest for ewes treated with ivermectin (20%) and was similar (40%) for ewes treated with 1 of the other 3 anthelmintics. At the conclusion of the study, most of the ewes (90%) were shedding at least a small number of eggs, regardless of the anthelmintic treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Anthelmintics for cattle

A number of anthelmintics are available for the control of gastrointestinal nematodes in cattle. In North America, O. ostertagi, Cooperia spp., lung worm, and F. hepatica probably cause the greatest losses in production. The older anthelmintics are often deficient in their action against some of these parasites. Recently, the Paratect morantel tartrate slow-release bolus has provided a mechanism for the prevention of infections with gastrointestinal nematodes and lung worm, to some extent, and this has been shown to produce considerable economic benefits. Fenbendazole removes arrested O. ostertagi larvae; thus, its availability is an important step in the prevention of type-2 ostertagiasis. It also has a very broad spectrum of activity that includes most other nematodes and tapeworms and is a very safe anthelmintic. Ivermectin is highly effective against almost all cattle nematodes and also has great value for the control of arthropod ectoparasites. In addition, it and levamisole are the only anti-nematode drugs that can be administered to cattle by injection. Clorsulon is a new, safe anthelmintic that provides good control of liver fluke and, thus, fills a gap in the control of helminths of cattle in North America. The efficient use of anthelmintics in association with management based on a knowledge of parasite epidemiology can ensure that cattle do not rapidly become re-infected. In this way, the benefits from the use of anthelmintics can be very considerable and far greater than the costs of control.

Efficacy of morantel tartrate on milk production of dairy cows: a field study

Eighty Holstein herds on Quebec Dairy Herd Analysis Service were paired into 40 blocks of two herds each to test the effects of systematic deworming with morantel tartrate. Cows in treated herds were given morantel tartrate in May, June, and July, and cows in control herds were given a placebo of ground corn, wheat bran, and barley; both products were administered at 1 kg/1000 kg body weight. Records were obtained from May 1983 to April 1984. Each farm was visited monthly from May to October 1983 to obtain herbage samples and fecal grab samples from a random 10% of lactating cows. Production records were obtained for the year prior to commencement of this trial for covariate analysis. Fecal worm egg counts and infective larvae counts in pasture were reduced by 83 and 93%, respectively, in treated herds. The pattern of worm egg excretion differed between groups due to repeated treatments with morantel. Treated herds produced 323 kg more milk per cow per yr and 1.2 kg per cow per d more fat-corrected milk than controls. Milk fat and protein percentages did not differ between groups for the 12 mo. Deworming lactating dairy cows at the beginning of and during the pasture season improved production performance.