moxidectin and Ostertagiasis

Eighty-eight lambs were allocated to one of four groups which were then dosed with 10,000 infective-stage larvae (L3) of one of four populations of Ostertagia circumcincta; the first (S) was an isolate known to be anthelmintic-susceptible; the second (OR) was a multiple anthelmintic-resistant isolate which had been recovered from the field following therapeutic failure of both ivermectin and moxidectin and subsequently maintained in the laboratory without further anthelmintic selection. The third (R) was derived from OR but had been passaged for five generations in the laboratory with each generation being screened with all three broad-spectrum drench families; the fourth (R x S) was an F1 cross between the S and R isolates. On patency, each of the four infection groups was sub-divided into five treatment groups, one of which received no anthelmintic while the others were administered either oral ivermectin (IVM-oral), controlled-release capsules containing ivermectin (IVM-CRCs), oral moxidectin (MOX-oral) or injectable MOX (MOX-inj). Neither formulation of IVM reduced FEC in the R, R x S and OR infected lambs compared to their untreated controls, but significant reductions were observed in all cases following MOX-oral or MOX-inj treatment. Similarly, neither IVM formulation significantly reduced the numbers of R or R x S worms compared to their untreated controls, although the numbers of OR worms were reduced in both cases (P<0.05). Direct comparisons of efficacy across the isolates, however, indicated that neither formulation was any more effective against R x S or OR worms than against the more highly selected R worms. In contrast, both MOX formulations significantly reduced worm numbers of all the resistant isolates compared to their respective untreated controls; furthermore, worm burdens of R x S were reduced significantly more than burdens of R (P<0.05). Reductions in OR burdens, which were intermediate between the two, did not differ significantly from either. The results are consistent with published work on Haemonchus contortus, which suggests that macrocyclic lactone (ML) resistance is expressed as a dominant trait under treatment with IVM. However, these data differ from the H. contortus studies in suggesting that ML resistance in O. circumcincta may effectively be rendered incompletely dominant or recessive by treatment with MOX.

Topics: Administration, Oral; Animals; Anthelmintics; Anti-Bacterial Agents; Delayed-Action Preparations; Drug Administration Schedule; Drug Resistance; Feces; Injections, Subcutaneous; Ivermectin; Macrolides; Ostertagia; Ostertagiasis; Parasite Egg Count; Sheep; Sheep Diseases

Two different deworming strategies based on the use of moxidectin, a broad spectrum endectocide with persistency against Ostertagia ostertagi, were evaluated in grazing dairy heifers. Eighty-four heifers unexposed to parasitic infection were randomly allocated to 3 different groups: untreated (Group 1), treated at 3 and 10 weeks after turnout with 0.5 mg/kg/body weight (BW) of topical moxidectin (Group 2), or treated at turnout and 10 weeks later with 0.5 mg/kg/BW of topical moxidectin (Group 3). The heifers were turned out on June 6 (Day 0) to a naturally contaminated pasture divided into 3 sections by an electrical fence. Each group of heifers was put on a different section of pasture. The trial ended when they were housed on October 29 (Day 143). The results of this experiment confirmed the beneficial effect of 2 strategic treatments with moxidectin pour-on under field conditions in Quebec. The parasitological parameters showed a statistical difference in terms of mean fecal egg counts between treated and control groups (ANOVA, P < or = 0.006). After turnout, pasture larval counts were consistently higher for Group 1 compared with counts for Group 2 or 3. All heifer groups gained weight during the trial period, but the weight gain profile of both treated groups was significantly higher than that of the untreated controls (ANOVA, P < 0.03). During the trial period, Group 2 and Group 3 gained 77.7 kg BW and 73.2 kg BW, respectively, while Group 1 gained only 57.9 kg BW, despite the fact that heifers of Group 1 received a greater quantity of supplementary feed while on pasture.

Topics: Abomasum; Analysis of Variance; Animals; Anti-Bacterial Agents; Antinematodal Agents; Cattle; Cattle Diseases; Feces; Female; Macrolides; Ostertagia; Ostertagiasis; Time Factors; Weight Gain

Topics: Administration, Oral; Animals; Anti-Bacterial Agents; Antinematodal Agents; Goat Diseases; Goats; Haemonchiasis; Haemonchus; Macrolides; Nematode Infections; Ostertagia; Ostertagiasis; Trichostrongylosis; Trichostrongylus

The persistence of the efficacy of moxidectin 0.5 per cent pour-on and moxidectin 1 per cent injectable against Ostertagia ostertagi and Dictyocaulus viviparus in calves was studied in two experimental trials. In the first trial two groups of seven calves were treated with either the pour-on or the injectable formulation, while a third group remained untreated. All the animals were infected daily from Monday to Friday with infective stages of O ostertagi and D viviparus between the day of treatment (day 0) and day 33, and were necropsied for worm counts three days later. The experimental design of the second trial was similar to that of the first but the period of infection was from 28 to 45 days after the treatment, and the necropsy was five days after the last infection. In both trials both moxidectin formulations had very high efficacies (99.6 per cent) against adult and developing stages of O ostertagi and D viviparus. The higher efficacy of the moxidectin pour-on preparation against early fourth stage larvae in both trials suggested that its effect was more persistent. It was calculated that the efficacy of moxidectin against O ostertagi persisted for at least five weeks for the injectable formulation and six weeks for the pour-on. The efficacy of moxidectin against D viviparus lasted for at least six weeks for both formulations.

Topics: Administration, Topical; Animals; Anthelmintics; Anti-Bacterial Agents; Cattle; Cattle Diseases; Dictyocaulus; Dictyocaulus Infections; Feces; Injections; Macrolides; Male; Ostertagia; Ostertagiasis; Parasite Egg Count; Time Factors

Topics: Animals; Anthelmintics; Anti-Bacterial Agents; Drug Resistance; Goats; Ivermectin; Macrolides; Ostertagia; Ostertagiasis; Parasite Egg Count; Sheep; Sheep Diseases

Topics: Administration, Topical; Animals; Anthelmintics; Anti-Bacterial Agents; Cattle; Cattle Diseases; Dictyocaulus Infections; Injections, Subcutaneous; Ivermectin; Macrolides; Male; Ostertagiasis; Treatment Outcome

Topics: Animals; Anthelmintics; Cattle; Cattle Diseases; Feces; Female; France; Germany; Ivermectin; Lactation; Macrolides; Milk; Ostertagia; Ostertagiasis; Parasite Egg Count; Pregnancy; United Kingdom

This paper describes the nematode control strategy adopted by a Scottish hill sheep farmer. It provides an example of the limited use of anthelmintic drugs, targeted towards control of the periparturient rise in faecal nematode egg output in ewes and exploitation of grazing management, resulting in limited exposure of naive sheep to infective larvae on pasture. Resistance to benzimidazole, imidazothiazole and macrocyclic lactone anthelmintics, and to a combination of a macrocyclic lactone and imidazothiazole anthelmintic drugs was diagnosed. The targeted use of a persistent anthelmintic drug to control a periparturient rise in faecal nematode egg output in ewes may be unnecessary and selects strongly for resistance when the reservoir of anthelmintic-susceptible nematodes in refugia is small at the time of treatment. However, the use of a persistent anthelmintic drug in a selective proportion of ewes can be important and probably does not select strongly for resistance when the reservoir of anthelmintic-susceptible nematodes in refugia is large at the time of treatment. The former circumstances might arise on many Scottish hill sheep farms, whereas the latter may occur on upland and lowground farms, depending on previous grazing management, anthelmintic use and winter weather conditions. These factors must be taken into account when preparing sustainable health plans for nematode parasite control in individual sheep flocks.

Topics: Animals; Animals, Newborn; Anthelmintics; Drug Resistance; Female; Macrolides; Ostertagia; Ostertagiasis; Pregnancy; Pregnancy Complications, Parasitic; Sheep; Sheep Diseases

Drug resistance in sheep gastrointestinal trichostrongyles is a cosmopolitan major constraint to small ruminant production. Despite reports that anthelmintic drug resistance has become common, there are limited information on the presence of drug resistance in Italy. The purpose of this study was to determine the effect of four anthelmintics to control infection in sheep in central Italy. Fifty sheep with fecal egg counts (FEC) > or =150 eggs per gram were selected on each of three farms (n = 150 total sheep) which were randomly allocated to one of five groups. Groups were treated with febantel, levamisole, ivermectin, or moxidectin while the fifth group acted as the control group. A FEC reduction test (FECRT) was conducted on each animal and the mean FEC of each treatment group was compared to that of the control group within farm. Resistance was declared when percentage reduction (R) <95% and the lower 95% confidence interval was <90%. Levamisole (mean R = 89%) resistance was found on all farms and ivermectin (mean R = 93%) resistance was found on two of the three farms. Posttreatment larval cultures showed the presence of Teladorsagia (Ostertagia) circumcincta and Trichostrongylus spp. larvae. Febantel (mean R = 96%) and moxidectin (mean R = 100%) remained effective. This study suggests that drug resistance in sheep gastrointestinal trichostrongyles is present in central Italy and a potential problem which would justify a broader nationwide geographical investigation.

Topics: Animals; Antinematodal Agents; Drug Resistance, Multiple; Feces; Guanidines; Italy; Ivermectin; Levamisole; Macrolides; Ostertagia; Ostertagiasis; Parasite Egg Count; Sheep; Sheep Diseases; Treatment Outcome; Trichostrongylosis; Trichostrongylus

To determine associations between resistance of Ostertagia (=Teladorsagia) spp to macrocyclic lactone (ML) anthelmintics and history of use of anthelmintics, by type, on commercial sheep farms in temperate regions of southern South Australia and Victoria, Australia.. Faecal egg count reduction tests (FECRTs) were conducted during a 2.5-year period (from August 2001 to January 2004) and records of the type of anthelmintic used in the 5 years preceding the FECRTs were collected from commercial sheep farms (n=103) in southern South Australia and Victoria, and data analysed retrospectively. ML resistance was defined as <95% reduction of Ostertagia spp 10-14 days after treatment with ivermectin (IVM), orally, at half the manufacturer's recommended dose rate. Use of anthelmintics in the preceding 5 and 10 years on each property was classified according to the nett number of years each of the following classes of drug had been used: IVM oral liquid (IVO), IVM controlled-release capsules (CRCs), abamectin (ABA), moxidectin (MOX) or a non-ML anthelmintic. The prevalence of ML resistance, by property, was analysed for associations with prior use of anthelmintics.. Resistance by Ostertagia spp to ML anthelmintics was evident on 51/103 (49.5%) properties. The prevalence of resistance was lowest (23%) on properties on which MOX had not been used, and was significantly higher (64-77%) on properties on which MOX had been used for > or =2 of the preceding 5 years (p<0.001). In contrast, the prevalence of resistance was highest (70-74%) on the properties on which IVM, or IVM and/ or ABA, had not been used in the previous 5 years (on which the use of MOX was predominant), and was markedly lower (20- 42%) on properties that had used IVM or IVM and/or ABA for at least one of the preceding 5 years. Prevalence of resistance was higher for properties on which the only ML anthelmintic used was MOX (19/29=66%) than for those on which the only ML used was IVO (2/19=11%; p<0.001). Properties on which the only ML used was MOX were 2.72 times more likely to have resistance than properties on which the only ML used was IVO (95% confidence interval (CI) = 1.01-5.08).. Use of MOX for > or =2 of the preceding 5 years was associated with a higher prevalence of resistance to ML by Ostertagia spp on sheep farms in south eastern Australia than the use of IVO.

Topics: Administration, Oral; Animal Husbandry; Animals; Anthelmintics; Australia; Drug Resistance; Drug Therapy, Combination; Feces; Female; Ivermectin; Macrolides; Male; Ostertagia; Ostertagiasis; Parasite Egg Count; Parasitic Sensitivity Tests; Prevalence; Random Allocation; Risk Factors; Sheep; Sheep Diseases; Treatment Outcome; Victoria

Sixty-four Romney ewe lambs were allocated to 12 groups on the basis of liveweight. Four groups (n=5) were administered oral ivermectin (IVM), 4 (n=6) oral moxidectin (MOX) and the remaining 4 (n=5) controlled-release capsules containing IVM (IVM-CRCs). Nine and 10 days later, the groups within each treatment type were challenged with infective-stage larvae (L3) of 1 of 4 different isolates of Teladorsagia circumcincta (two doses each of 5000 L3). The first of these (S) was known to be anthelmintic-susceptible; the second (OR) was a multiple anthelmintic-resistant strain recovered from the field following therapeutic failure of both ivermectin and moxidectin and subsequently maintained in the laboratory without further anthelmintic selection; the third (R) was derived from OR but had been passaged for five generations indoors with each generation being screened with all three broad-spectrum anthelmintic classes; and the fourth (RxS) was an F1 cross between the R and S isolates. As anticipated, because of its limited residual activity, IVM had no significant effect on the establishment, 9 and 10 days post-treatment, of any of the parasite isolates. In contrast MOX, which has greater residual activity, was highly effective at preventing the establishment of the S isolate but showed no significant effect against the OR, R or RxS isolates. The IVM-CRC was also highly effective at preventing the establishment of the S isolate and furthermore it significantly reduced establishment of both the OR and RxS isolates, although it had no significant effect against the R isolate. The results suggest that with respect to the establishment of T. circumcincta L3s following anthelmintic treatment, macrocyclic lactone (ML) resistance is effectively a dominant trait in the presence of MOX, while it behaves as a partially dominant/recessive trait under treatment with IVM-CRCs. The potential implications of this finding in relation to selection for ML resistance in T. circumcincta are discussed.

Topics: Abomasum; Administration, Oral; Animals; Anthelmintics; Delayed-Action Preparations; Drug Resistance; Feces; Female; Intestinal Diseases, Parasitic; Ivermectin; Macrolides; Ostertagia; Ostertagiasis; Parasite Egg Count; Random Allocation; Sheep; Sheep Diseases

Topics: Animals; Anthelmintics; Anti-Bacterial Agents; Disease Outbreaks; Disease Susceptibility; Feces; Female; Macrolides; Ostertagia; Ostertagiasis; Parasite Egg Count; Postpartum Period; Seasons; Sheep; Sheep Diseases

The observation that the total abundance of adult nematodes in the abomasum of Svalbard reindeer increases between October and April suggests adaptation to cope with the Arctic winter. Here we investigate the extent to which selection has led to similar life-history strategies in the 3 most numerous trichostrongyle species. The life-histories are found to differ markedly. We use flexible statistical models for the abundance and dispersion of parasites in the host population. One of the taxa, Marshallagia marshalli, was most abundant and had its highest egg output in the winter. In contrast, the abundance of the most common taxa, Ostertagia gruehneri, m. gruehneri was stable or declined from autumn to late winter, and the closely related taxa, O. gruehneri, m. arcticus, showed a similar over winter drop. The faecal egg output of these 2 taxa was highest in summer, as found in temperate trichostrongyle species. Despite the apparent contamination of summer pastures with O. gruehneri, calves showed negligible burdens until their second summer and the abundance of infection reached an asymptote within their third year. In contrast, the abundance of M. marshalli in calves showed a rapid increase over the first summer and by late winter was similar to peak levels found in adults (8000 worms). This increase could not be accounted for by the developing abomasum larvae population and is therefore evidence for transmission over the winter for this taxa. While M. marshalli showed little between-year variation, O. gruehneri showed 2-fold fluctuation in the abundance of infection. O. gruehneri may therefore play a role in the fluctuating population dynamics of the host. Since there was no apparent decline in abundance with host age in any of the 3 taxa there was no evidence of reindeer mounting an immune response.

Topics: Abomasum; Age Factors; Animals; Anthelmintics; Anti-Bacterial Agents; Arctic Regions; Binomial Distribution; Feces; Female; Macrolides; Male; Models, Biological; Norway; Ostertagia; Ostertagiasis; Parasite Egg Count; Population Dynamics; Prevalence; Random Allocation; Reindeer; Seasons; Trichostrongyloidea; Trichostrongyloidiasis

In order to determine whether the efficacy of moxidectin against Ostertagia circumcincta is enhanced by its persistency, therapeutic efficacy was compared at intervals after treatment and with that of ivermectin, a closely related but more transient endectocide. Groups of 7-month-old New Zealand Romney lambs were infected with a strain of O. circumcincta known to be resistant to moxidectin. At patency of the infections, groups of lambs were treated with either moxidectin or ivermectin at the manufacturer's recommended dosages, or left untreated. At 3, 6 and 10 days post-treatment, faecal egg count was measured and groups of lambs were slaughtered for estimation of adult worm burden. Drug-resistant worm burdens were significantly reduced in those animals treated with moxidectin but not in those treated with ivermectin. No effect of time of slaughter on worm burden was observed with either drug, demonstrating that the higher therapeutic efficacy of moxidectin against this parasite was not due to an increased period of drug exposure. Faecal egg counts in the moxidectin treated animals increased with time after treatment indicating a temporary suppression of egg output by surviving worms. The implications of these findings on selection for anthelmintic resistance are discussed.

Topics: Animals; Anthelmintics; Anti-Bacterial Agents; Drug Resistance; Feces; Ivermectin; Macrolides; Ostertagia; Ostertagiasis; Parasite Egg Count; Sheep; Sheep Diseases

The nematocidal effectiveness of moxidectin, administered topically at the rate of 500 mcg/kg BW, was determined for lactating dairy cows. Naturally infected animals were given either topical vehicle or moxidectin (Cydectin Pour-On Fort Dodge Animal Health) at the rate of 1 ml/10 kg BW (10 animals per treatment group), and sacrificed 14-18 days post-treatment for nematode enumeration. 100% efficacies were recorded for Ostertagia lyrata males, Cooperia punctata males and Oesophagostomum radiatum L4, with treatment group differences in geometric means significant (P < 0.05) for all. Populations of Trichostrongylus L4 and adult O. radiatum were also reduced by 100%, but low prevalence rates in the control animals precluded meaningful statistical inference. Nematode populations for which efficacies ranged from 96.7 to 99.6% (based on geometric means) and for which treatment group differences were significant (P < 0.05) included Ostertagia spp. adult females, inhibited L4 and developing L4, O. ostertagi adult males, Trichostrongylus axei adults and Cooperia spp. adult females. For all nematodes combined, moxidectin was 98.9% efficacious. In addition to exhibiting excellent nematocidal effectiveness, topical moxidectin was demonstrated to be safe, with animal health and milk production unaffected during the study.

Topics: Abomasum; Administration, Topical; Animals; Anthelmintics; Anti-Bacterial Agents; Cattle; Cattle Diseases; Female; Intestine, Large; Intestine, Small; Lactation; Macrolides; Male; Nematode Infections; Oesophagostomiasis; Oesophagostomum; Ostertagia; Ostertagiasis; Parasite Egg Count; Prevalence; Random Allocation; Trichostrongyloidea; Trichostrongyloidiasis

The persistent activity of moxidectin topically administered at the dose rate of 0.5 mg kg-1 bodyweight was evaluated against experimental nematode infection in 30 calves randomly allocated to six groups. Five groups were treated on days -42, -35, -28, -21 and -14. The 6th group remained untreated as a control. On Day 0, the calves were infected experimentally with 1000 Dictyocaulus viviparus and 50,000 Ostertagia ostertagi larvae and killed 3 weeks later. The formulation of moxidectin showed excellent activity against both parasites for up to 5 weeks (> 99%). Six weeks after treatment the reduction in the number of D. viviparus was still high (> 90%). No adverse reactions to moxidectin were observed in any of the animals.

Topics: Administration, Topical; Animals; Anthelmintics; Anti-Bacterial Agents; Cattle; Cattle Diseases; Dictyocaulus Infections; Larva; Macrolides; Ostertagiasis; Time Factors

Three groups of newly-weaned Romney lambs were given either a standard oral dose of albendazole, a controlled-release capsule containing albendazole, or a standard oral dose of moxidectin. At 10, 20, 30 and 40 days after treatment, sub-groups of lambs were given 10,000 infective-stage larvae of either a drug-resistant or a drug-susceptible strain of Ostertagia circumcincta. The recommended oral dose of albendazole removed 32 per cent of the resistant strain and over 99.9 per cent of the susceptible O. circumcincta. The recommended oral dose of moxidectin removed 91 per cent of the resistant strain and over 99.9 per cent of the susceptible parasites. None of the lambs treated with controlled-release capsules was challenged at 20 or 30 days after treatment. Twenty-one days after challenge, samples of faeces were taken to determine the presence of nematode eggs and cultured to establish the proportion of eggs developing to infective-stage larvae (L3). Abomasa were recovered after slaughter and worm burdens determined. In the lambs given controlled-release capsules only the resistant parasites were able to establish, and there were significantly fewer than in the lambs treated orally with albendazole. The proportion of the eggs from resistant parasites which developed to L3 was not reduced by the presence of the capsules. Oral moxidectin provided no protection against the establishment of the resistant strain and viable L3 were recovered after challenge with resistant parasites 10 days after treatment; however, the establishment of susceptible O. circumcincta was reduced by more than 99 per cent. The establishment of the susceptible parasites in the lambs treated with moxidectin increased with time and was not significantly lower than in the other groups by 30 days after treatment.

Topics: Administration, Oral; Albendazole; Animals; Anthelmintics; Anti-Bacterial Agents; Delayed-Action Preparations; Drug Resistance; Macrolides; Ostertagia; Ostertagiasis; Sheep; Sheep Diseases

The persistent efficacy of some anthelmintics brings advantages in nematode control in domestic animals. However, scientific assessment of persistent efficacy is relatively new, and a feature of published data has been variability in the reported endpoint for this activity. Trial design and method of calculating efficacy have a large bearing on the results obtained. Three types of studies used to evaluate the persistent efficacy of anthelmintics are briefly discussed and compared. In the first type of study, animals are treated followed by a single infection at 7, 14 or more days after treatment. The reduction in worm counts compared to an untreated control group gives a good indication of the persistent efficacy of the product at each time point. One control group can be used for several time points. In the second type of study, the animals are treated and then infected daily from day 1 until 7 days, 14 days or longer after treatment. The animals are slaughtered approximately 3 weeks after the last infection. This approach may better mimic a natural infection but the results obtained are an average reduction over the whole infection period. At the end of the evaluated period, the actual protection may be considerably lower than the average. From this test, it is difficult to define when the protection decreases or disappears. In this test, a control group is required for each period. In the third type of study, a modification of the second, the animals are treated and infected as before but animals are slaughtered soon (2-5 days) after the last infection. Based on the reduction of, for example, the different Ostertagia stages a more specific determination of the persistent efficacy 0-3 days (L3), 3-7 (EL4), 7-14 (LL4 + EL5) and more than 14 days (LL5 + adults) before slaughter can be obtained. Only two groups of animals are required to cover a 3 week period and the average efficacies can be reduced to about one week.

Topics: Animals; Animals, Domestic; Anthelmintics; Anti-Bacterial Agents; Clinical Protocols; Ivermectin; Macrolides; Nematoda; Nematode Infections; Ostertagiasis; Reproducibility of Results; Research Design

Topics: Animals; Anthelmintics; Anti-Bacterial Agents; Cattle; Cattle Diseases; Female; Macrolides; Ostertagia; Ostertagiasis

Topics: Animals; Anthelmintics; Anti-Bacterial Agents; Drug Resistance; Feces; Female; Goat Diseases; Goats; Ivermectin; Macrolides; Ostertagia; Ostertagiasis; Parasite Egg Count

Topics: Abomasum; Animals; Anthelmintics; Anti-Bacterial Agents; Cattle; Cattle Diseases; Dictyocaulus; Dictyocaulus Infections; Injections, Subcutaneous; Lung; Macrolides; Male; Ostertagia; Ostertagiasis; Random Allocation

Topics: Animals; Anthelmintics; Anti-Bacterial Agents; Goat Diseases; Goats; Macrolides; New Zealand; Ostertagiasis

Topics: Administration, Topical; Animals; Anthelmintics; Anti-Bacterial Agents; Cattle; Cattle Diseases; Feces; Female; Injections, Subcutaneous; Macrolides; Ostertagia; Ostertagiasis; Parasite Egg Count; Trichostrongyloidea; Trichostrongyloidiasis

To determine whether there is mutual resistance to avermectin and milbemycin anthelmintics, ivermectin and moxidectin sheep drenches were tested against ivermectin-resistant and susceptible isolates of Ostertagia circumcincta and Trichostrongylus colubriformis in sheep. None of the isolates had been exposed to moxidectin previously. The dosage of ivermectin required to remove 95 per cent of the ivermectin-resistant O circumcincta and T colubriformis were 23 times and six times larger, respectively, than the dosages required to remove the same percentage of susceptible isolates. The dosages of moxidectin required to remove 95 per cent of the ivermectin-resistant O circumcincta and T colubriformis were 31 times and nine times larger, respectively, than the dosages required to remove the same percentage of susceptible isolates. It is concluded that the worms resistant to ivermectin were also resistant to moxidectin.

Topics: Administration, Oral; Animals; Anthelmintics; Anti-Bacterial Agents; Drug Resistance; Female; Ivermectin; Macrolides; Male; Ostertagia; Ostertagiasis; Random Allocation; Sheep; Sheep Diseases; Trichostrongylosis; Trichostrongylus

Topics: Animals; Anthelmintics; Anti-Bacterial Agents; Drug Resistance; Ivermectin; Macrolides; Ostertagia; Ostertagiasis; Sheep; Sheep Diseases

Three groups of 11 naturally infected crossbred beef calves were injected subcutaneously with moxidectin 1 per cent injectable at 0.2 or 0.3 mg moxidectin/kg bodyweight or with the unmedicated vehicle. Nematode infections had been acquired during grazing from December to April. Based on the faecal egg counts and total worm counts of the control calves at necropsy (11 to 13 days after treatment) most of the calves had heavy parasitic burdens. Ostertagia ostertagi was predominant and the mean numbers of adults, developing fourth stage larvae (L4) and inhibited early L4 were 45,906, 10,061 and 68,918, respectively. Haemonchus placei and Trichostrongylus axei were also present in the abomasa. Three species of Cooperia, Oesophagostomum radiatum L4 and T colubriformis adults were found in the intestinal tract. Both dosages of moxidectin were equally effective (P < 0.05) against all the abomasal nematodes (99.9 to 100 per cent) and the intestinal tract nematodes (99.4 to 100 per cent). No adverse reactions to the moxidectin treatment were observed. Abomasal pathology characteristic of heavy O ostertagi infection was observed in the control calves, but not in the treated calves.

Topics: Animals; Anthelmintics; Anti-Bacterial Agents; Cattle; Cattle Diseases; Feces; Female; Haemonchiasis; Intestinal Diseases, Parasitic; Macrolides; Nematode Infections; Oesophagostomiasis; Ostertagiasis; Parasite Egg Count; Trichostrongyloidiasis; Trichostrongylosis