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1.
DM Leathwick TS Waghorn CM Miller DS Atkinson NA Haack A-M Oliver 《New Zealand veterinary journal》2013,61(6):305-312
AIM: To determine whether drenching regimes for lambs by which a proportion (10%) of the heaviest animals was selectively left untreated, or animals are only drenched ‘on demand’ when faecal nematode egg counts (FEC) exceeded a threshold level, would result in measurable increases in parasite larval challenge in the autumn and/or decreases in the performance of lambs. METHODS: A replicated study compared three drenching strategies in which mobs of lambs (n=360 in total) received either: a five-drench preventive programme, administered to all animals (Treatment 1); a five-drench preventive programme, but the 10% heaviest animals left untreated each time (Treatment 2); or drench treatments administered only when FEC exceeded 500 eggs per gram of faeces (epg) (Treatment 3). After the five-drench programme, animals in Treatments 1 and 2 were treated according to FEC as for Treatment 3. A triple-combination drench containing ivermectin, oxfendazole and levamisole, administered orally, was used for all treatments. There were nine farmlets, allowing three replicates of each treatment, in a completely randomised design. Parasite infestations on pasture were measured in autumn by pasture plucks, and worm burdens were monitored in tracer lambs, while the performance of lambs was assessed by liveweight gains, fleece weights, and body condition and dag scores. RESULTS: Increased numbers of Haemonchus contortus and Trichostrongylus colubriformis larvae on pasture were found in the autumn on farmlets treating selectively or on-demand (Treatments 2 and 3). No differences were detected in other parasite species. Mean liveweight gains did not differ between treatments but some differences were detected between drenched and undrenched lambs in Treatment 2. Mean body condition and mean dag scores of lambs in Treatment 3 tended to be lower and higher, respectively, than those of lambs in Treatment 1; Treatment 2 was generally intermediate. CONCLUSIONS: Drenching strategies for lambs designed to slow the development of anthelmintic resistance, by increasing the pool of susceptible worms available to dilute resistant survivors after treatment, resulted in increased numbers of H. contortus and T. colubriformis but not other species of parasite on pasture. The increased parasite challenge to lambs in the autumn was associated with small production losses, which may be acceptable to farmers wishing to implement such strategies. It is clear that further work is required on the interaction between management practices and the population dynamics of parasites, especially with regard to creating pools of susceptible genotypes to slow the development of drench resistance. 相似文献
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Beckett FW 《New Zealand veterinary journal》1993,41(3):116-122
The effectiveness of a commonly advocated five drench preventive drenching programme in lambs was assessed on nine farms in the Gisborne, Hawkes Bay and Wairarapa districts between December 1983 and March 1985. The productive performance of two groups of preventively drenched lambs was compared with lambs in which parasitism was suppressed by fortnightly drenching from weaning until mid-August 1984. One of the groups received the standard five drench programme commencing at weaning and finishing in March 1984. The other group received six additional 4-weekly drenches, with the last drench in mid-August 1984. All the other lambs on the farms were drenched according to the five drench programme. The availability of infective larvae on pasture and the build-up of parasitic infection in the lambs was monitored. The effects of the different drenching programmes on liveweight and faecal egg counts was followed until March 1985, when the animals were 18 months old. Between March and July 1984 on all nine farms there was a significant depression of growth rates of the standard five drench group when compared with the suppression-drenched group (P<0.01). The mean liveweight difference from December 1983 to July 1984 for all farms was 4.0 kg (P<0.05). Hogget wool weights were significantly depressed (mean difference 0.37 kg, P<0.05). Faecal egg counts rose steadily after the completion of the five drench programme in March, exceeding 1000 eggs per gram on seven farms and 4000 eggs per gram on three of these farms. Trichostrongylus spp. was the major constituent of the winter parasite increase except on one farm when Cooperia spp. succeeded a previous Haemonchus dominance. Two farms had major build-ups of Haemonchus spp., one in early May, the other in June. Six farms salvage-drenched the standard five drench groups. The lambs in the standard drench groups on these farms recovered about half the bodyweight difference between August and March. The mean weight gains to July and wool weights of the modified drench programme groups were reduced slightly compared with the suppression-drenched group (mean liveweight difference 1.4 kg; mean wool weight difference 0.15 kg). No major rises in faecal egg counts occurred. Herbage larval counts exceeded 1000 larvae/kg at some stage on seven farms and, of these, the counts exceeded 4000 larvae/kg on three farms. 相似文献
5.
Leathwick DM Miller CM Atkinson DS Brown AE Green RS Sutherland IA 《New Zealand veterinary journal》2002,50(2):70-76
AIMS: To determine whether: a) using a controlled-release anthelmintic capsule (CRC) instead of a programme of 5 oral drenches administered at 3-4 week intervals, would delay the development of anti-parasite immunity in lambs; b) the use of ivermectin instead of albendazole, administered either as a CRC or as a programme of 5 oral drenches, would delay the development of anti-parasite immunity in lambs; c) lambs treated with CRCs would have higher liveweight gains than lambs drenched orally 5 times at 3-4 week intervals, and; d) delayed onset of anti-parasite immunity is associated with reduced liveweight gains in the period following anthelmintic treatment. METHODS: Three field trials were conducted, 1 on a research farm and 2 on commercial sheep farms, in which groups of 30 lambs were treated with either a CRC containing albendazole, a CRC containing ivermectin, 5 oral drenches with albendazole, or 5 oral drenches with ivermectin, administered at 3-4 week intervals. Liveweights and faecal nematode egg counts (FECs) were recorded in all trials. Immunoglobulin-G (IgG) antibody levels to Ostertagia circumcincta and Trichostrongylus colubriformis adult and larval antigens were measured in Trials 1 and 3, and fleece weights and resistance of animals to nematode challenge infection were measured in Trial 1. RESULTS: CRC-treated lambs had higher levels of antibodies to O. circumcincta infective-stage larvae (L3) than orally drenched lambs in Trial 3, but no other immunological differences due to mechanism of delivery were detected. Antibody levels were lower in lambs treated with ivermectin than albendazole, as a CRC or oral drench in Trial 1, but this was not associated with any measurable effects on FEC or productivity. No significant differences (p>0.05) were detected between drench types (albendazole vs ivermectin) or delivery mechanisms (CRC vs oral drenching) in any of the production parameters measured, in any of the trials. Albendazole-CRCs failed to control FECs in all 3 trials. CONCLUSIONS: Although some differences between treatments in antibody levels were detected these were not associated with measurable differences in level of parasitism or productivity of lambs. CRC use did not appear to offer substantial gains in productivity over a structured programme of 5 oral drenches administered at 3-4 week intervals. 相似文献
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Lamb parasitism and performance were compared on three pasture treatments: browntop/white clover, Yorkshire fog/white clover, and ryegrass/white clover swards maintained at a sward height of 5cm in each of two years by using continuous variable stocking management. In year 1, lamb performance (both suppressively drenched (SD) and trigger drenched (TD)) was similar on ryegrass and browntop swards but was poorer (P<0.05) on Yorkshire fog swards. In year 2, lamb performance (both SD and TD) was markedly better on ryegrass than on Yorkshire fog or browntop swards. This coincided with an increase in white clover content in the ryegrass/white clover swards and a decrease in white clover content in the browntop/white clover swards. Lamb performance was related to the white clover content of the swards (R2=85.4, P<0.001 and R2=77.5, P<0.001 for SD lambs and TD lambs, respectively). Differences among pasture treatments in faecal egg count (FEC) of TD lambs were greater in year 2 than in year 1 when no significant pasture effects were observed. In year 2, FEC was lowest in lambs which grazed ryegrass/white clover, intermediate in those which grazed Yorkshire fog/white clover and highest in lambs which grazed browntop/white clover, despite herbage allowance (kg herbage mass/kg lamb mass) being greater on the browntop/white clover and Yorkshire fog/white clover swards than the ryegrass/white clover swards. Circulating antibodies to gastrointestinal parasites were measured at the end of year 2. Antibody titres were highest (P<0.05) in the plasma of lambs which grazed ryegrass/white clover swards, and lowest in lambs which grazed browntop/white clover swards due to differences in levels of antibody to (P<0.05) Haemonchus contortus, Ostertagia circumcincta larvae and adults, but not Trichostrongylus colubriformis larvae or adults. These findings indicate that pasture composition, especially, the proportion of white clover, can help alleviate the production losses due to gastrointestinal parasitism. This information can provide a quick and readily adoptable practice for farmers who aim to reduce drench reliance and could become a key component of any integrated parasite control programme. 相似文献
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AIMS: To determine the incidence of ruminoreticulum bypass in lambs before and after weaning, following drenching with anthelmintic-equivalent volumes of fluid; to investigate the influence of withholding feed for 24 hours before drenching on the incidence of ruminoreticulum bypass; and to investigate the hypothesis that ruminoreticulum bypass occurs more frequently following drenching with large than with low volumes. The relationship between these factors and the efficacy of benzimidazole anthelmintic drenches has been widely promoted in New Zealand and Australia. METHODS: Video-taped fluoroscopy, using barium sulphate suspension with a specific gravity of 1.38 as a contrast medium, was used to study closure of the reticular groove and ruminoreticulum bypass in sheep. RESULTS: When lambs were drenched with 3 ml of barium sulphate suspension/10 kg liveweight soon after removal from pasture, ruminoreticulum bypass only occurred before weaning and during the first 8 weeks after weaning. However, when a low volume drench (1 ml/10 kg) was used in lambs soon after removal from pasture during the same period, ruminoreticulum bypass was not observed. When recently weaned lambs were yarded for 24 hours before drenching with barium sulphate suspension, substantial (> or = 20%) ruminoreticulum bypass occurred in 25-58% of the animals. When 8-9 month-old hoggets were yarded for 24 hours before drenching, substantial ruminoreticulum bypass occurred in 35% of the animals. Ruminoreticulum bypass was not observed in the same group of hoggets when drenched soon after removal from pasture, in a reversed crossover experiment. This effect of withholding feed for 24 hours on ruminoreticulum bypass was significant (p < 0.0001). In hoggets which had been yarded for 24 hours before drenching with barium sulphate suspension, the incidence of ruminoreticulum bypass was significantly lower (p = 0.0026) following the use of a low volume (1 ml/10 kg) when compared to high volume (3 ml/ 10 kg) of drench. Thus, the effect of withholding feed for 24 hours on ruminoreticulum bypass was largely overcome when the low volume drench was used. CONCLUSIONS: These results support the use of low volume formulations of benzimidazole drenches for New Zealand pasture-fed lambs less than 6 months old. The results indicate that, in order to obtain the optimum efficacy of benzimidazole anthelmintics in New Zealand pasture-fed sheep, which have been yarded for 24 hours, low volume drench formulations should be used. 相似文献
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Fifty, 5-6 month-old lambs were randomly allocated to five equal groups. Three groups of lambs were immunised by three oxfendazole-abbreviated (artificial) infections of Trichostrongylus colubriformis and Ostertagia circumcincta. Group 1 was immunised with a high dose of larvae, Group 2 with a medium dose and Group 3 with a low dose. A fourth group was treated with oxfendazole only and a fifth group was not treated (control). All groups were grazed together on pasture naturally contaminated with nematode larvae. Immunisation significantly reduced the number of eggs per gram of faeces in all three groups, but the lowest faecal egg count was seen in Group 3 (immunised with the lowest number of larvae). Significantly better liveweight gains and wool weight were observed in Group 2 animals than in the control group. Of all anthelmintic-treated animals, only Group 1 lambs did not have a significantly lower dag weight than controls. 相似文献
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Predicting the impacts of selection for decreased faecal egg count (FEC) (i.e. host resistance) in grazing ruminants is difficult, due to complex interactions between parasite epidemiology, management and host responses. A mathematical model including heritable between lamb variation in host-parasite interactions, Teladorsagia circumcincta epidemiology and anthelmintic drenching, was developed and used to (i) address such interactions and their impact on outcomes including FEC, live weight (LW, kg) and pasture larval contamination (PC, larvae/kg DM), and (ii) investigate how grazing management strategies, aimed at reducing host exposure to infective larvae via pasture moves at 40 day intervals, affect these outcomes. A population of 10,000 lambs was simulated and resultant FEC predictions used to assign the 1,000 lambs with the highest and lowest predicted FEC to 'susceptible' (S) and 'resistant', (R) groups, respectively. The predicted average FEC of the S group was ～8.5-fold higher than the R group across a grazing season. The R and S groups were then simulated to graze separate pastures (R(sep) and S(sep)); and repeated for 3 grazing seasons to allow predictions to diverge and stabilize. Further, different grazing strategies were superimposed on all groups. PC and average FEC were affected by whether lambs of different resistance genotype grazed together or separately, with differences increasing across grazing seasons. By the third grazing season the average PC of the R(sep) group was reduced by ～83%, and the S(sep) group was increased by ～240%, in comparison to the whole population average. Average FEC of the R(sep) group was reduced by ～40%, and the S(sep) group increased by ～46% in comparison to the R and S groups, respectively, whilst drenching had little impact on the proportional differences in FEC between groups. Predicted LW was similar for the R and R(sep) groups irrespective of anthelmintic treatment, whilst LW of the S(sep) group was reduced by ～14% compared to the S group for un-drenched lambs, and by ～4% for drenched lambs. The differing grazing strategies were predicted to have little impact on FEC or LW, with the exception of the S(sep) group which was predicted to have a 2kg increase in LW when drenched and moved to a clean pasture. Together, these results suggest that host genotype has a substantial impact on parasite epidemiology, however the benefits of anthelmintic treatment and grazing management should only be expected for susceptible animals. This supports the use of targeted selective treatment, focussing on susceptible animals. 相似文献
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Lambs weaned at eight weeks old were compared with control lambs which remained with their dams; both groups grazed the same pasture. Weaning significantly reduced the growth rate, control lambs being, on average, 6 kg heavier than weaned lambs at 15 weeks old. When contamination of pasture with larval parasites was light, both groups of lambs suffered only modest parasitic infections. When lambs were experimentally infected with 5000 Haemonchus contortus and 10,000 Trichostrongylus colubriformis larvae at eight weeks old, the mean faecal egg count for weaned lambs was twice that for controls at 12 weeks old (P less than 0.001) and weaned lambs suffered a significantly greater decline in packed cell volume than controls over the next four weeks. Antibody responses following immunisation with either ovalbumin or Brucella abortus at four and at eight weeks old, did not differ significantly between control and weaned lambs. In contrast serum antibody responses to H contortus and T colubriformis differed significantly between the two groups, with controls responding earlier and more strongly than weaned lambs. The practical significance of these findings is that up to three months old, suckled lambs, when faced with a substantial parasite challenge, have much better prospects than weaned lambs. 相似文献
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B.H. Simpson B.V.Sc. 《New Zealand veterinary journal》2013,61(3):24-28
A sample survey of anthelmintic usage and farmers' drenching policies was conducted on 614 sheep farms, in the North and South Islands, selected from among those carrying 1500 or more breeding ewes. The survey was based on information for the 1978/79 and 1979/80 farming years recorded on questionnaires completed during personal interviews between Livestock Officers and the farmers concerned. Results show that there were no significant between-Island differences in mean drenching frequencies for any age class of sheep. In 1979/80, the overall New Zealand drenching frequencies were 6.3 for lambs, 1.8 for 1-2-year-olds and 1.2 for sheep older than 2 years. Of the farmers surveyed, 20% did not drench 1-2-year-old sheep and 29% did not drench sheep older than 2 years. There were also no between-Island differences in timing of drenches and alternation of drench brands. Sixty-nine per cent of the farmers followed a pre-determined drenching programme whereas 27% stated that they drenched if and when necessary. For lambs, some drenching was carried out in all months of the year but fewer farmers drenched during the mid-winter to mid-spring period (July-October). Older stock were drenched in all months also but there was a general acceptance by farmers of the practices of pre-tupping and pre- or post-lambing drenching. At the time of the survey, 48% of the farmers were using three or more brands of drench with a maximum of nine. Analysis of data relating to brands of drench used shows that whereas 39% of the farmers were alternating drench families [i.e. benzimidazoles (BZ) c.f. non-benzimidazoles (NBZ)] within a single farming year, only 3% were practising a strict alternation of drench families between years. General comments by the farmers surveyed indicate a disturbing degree of misunderstanding and misconception regarding the properties and limitations of current anthelmintics. The survey also revealed a lack of appreciation of the rationale of prophylactic (‘preventive’) parasite control. These aspects are discussed in relation to currently recommended control strategies and the problem of anthelmintic resistance. 相似文献
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A sample survey of anthelmintic usage and farmers; drenching policies was conducted on 614 sheep farms, in the North and South Islands, selected from among those carrying 1500 or more breeding ewes. The survey was based on information for the 1978179 and 1979/80 farming years recorded on questionnaires completed during personal interviews between Livestock Officers and the farmers concerned. Results show that there were no significant between-Island differences in mean drenching frequencies for any age class of sheep. In 1979/80, the overall New Zealand drenching frequencies were 6.3 for lambs, 1.8 for 1-2-year-olds and 1.2 for sheep older than 2 years. Of the farmers surveyed, 20% did not drench 1-2-year-old sheep and 29% did not drench sheep older than 2 years. There were also no between-Island differences in timing of drenches and alternation of drench brands. Sixty-nine per cent of the farmers followed a pre-determined drenching programme whereas 27% stated that they drenched if and when necessary. For lambs, some drenching was carried out in all months of the year hut fewer farmers drenched during the mid-winter to mid-spring period (July-October). Older stock were drenched in all months also but there was a general acceptance by farmers of the practices of pre-tupping and pre or post-lambing drenching. At the time of the survey, 48% of the farmers were using three or more brands of drench with a maximum of nine. Analysis of data relating to brands of drench used shows that whereas 39% of the farmers w,ere alternating drench families [i.e. benzimidazoles (BZ) c.f. non-benzimidazoles (NBZ)] within a single farming year, only 3% were practising a strict alternation of drench families between years. General comments by the farmers surveyed indicate a disturbing degree of misunderstanding and misconception regarding the properties and limitations of current anthelmintics. The survey also revealed a lack of appreciation of the rationale of prophylactic (;preventive;) parasite control. These aspects are discussed in relation to currently recommended control strategies and the problem of anthelmintic resistance. 相似文献
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Brave or gullible: testing the concept that leaving susceptible parasites in refugia will slow the development of anthelmintic resistance 总被引：1，自引：0，他引：1
AIM: To test the theory that creating a reservoir of unselected worms by leaving a proportion of lambs in a flock untreated with anthelmintic, i.e. in refugia, will slow the development of anthelmintic resistance in nematode parasite populations. METHODS: Newly weaned Romney lambs (n=180) were infected with two nematode parasite species, Teladorsagia (= Ostertagia) circumcincta and Trichostrongylus colubriformis. For each species, the challenge doses contained a mixture of infective larvae from benzimidazole-resistant and -susceptible isolates calculated to yield, from the combined population, a 95% reduction in faecal nematode egg counts (FEC) following treatment with albendazole. Once the infections were patent, the lambs were divided into nine groups of 20 animals, and each group was allocated to one of three treatments. In Treatments 1, 2 and 3, 100%, 90% and 80% of animals were treated with an anthelmintic, respectively. For treatments 2 and 3, the heaviest animals remained untreated. Following treatment, each group was moved to its own previously prepared low-contamination pasture. Lambs grazed this pasture for 7 weeks before again being treated and moved to new low-contamination pastures (Shift 1 and Shift 2). The parasite populations on pasture resulting from the different treatments were subsequently sampled using tracer lambs, and worm eggs derived from these were used in both egg-hatch assays (EHA) and larval development assays (LDA), to measure albendazole-resistance status. RESULTS: Treating all animals each time the groups were moved to new low-contamination pastures resulted in higher levels of albendazole resistance (p<0.05), measured using EHA and LDA, in subsequent parasite generations than when either 10 or 20% of animals were left untreated. However, higher FEC in the tracer lambs grazed on pastures in Treatments 2 and 3, compared with Treatment 1, indicated an increased level of pasture contamination as a result of leaving some animals untreated. CONCLUSIONS: The results demonstrate that creating a reservoir of unselected parasites slows the development of anthelmintic resistance, and emphasises the risk of treating all animals prior to a shift on to low-contamination pasture. However, higher levels of pasture contamination, resulting from untreated animals, indicate the difficulty in managing both worm control and resistance. 相似文献
14.
van Wyk JA Meyer J van Rensburg LJ 《Journal of the South African Veterinary Association》2003,74(1):2-6
As part of a trial to test the profitability of finishing weaner lambs over winter and spring on the Highveld of Gauteng province, an investigation was carried out over 4 consecutive years as to whether or not worm control was necessary while the lambs were on irrigated, improved pastures. Pastures that had not been grazed by sheep or other livestock for at least 5 years were planted to annual ryegrass (Lolium multiflora) that was ploughed under and replanted annually. Weaner lambs were randomly divided into either 2 (A and B) or 3 (A, B and C) groups and finished from April/May to November/December on a separate pasture per group. While Group A lambs were dewormed before being placed on pasture, those in Groups B and C were not. Faecal egg counts were performed at irregular intervals, and when the lambs were sold at the conclusion of each year's trial, the gastrointestinal tracts of 4-5 lambs per trial group were processed for worm recovery. Haemonchus contortus was the dominant worm species, while Trichostrongylus colubriformis, Ostertagia circumcincta and Trichuris spp. were encountered sporadically. From the results obtained it seems unlikely that there is appreciable 'carry-over' of the various worm species from year to year on pastures that are ploughed and replanted annually; thus it is improbable that there will be a build-up of anthelmintic-resistant worms. While on pasture, no drenching was required for the Group A lambs (dewormed before placing on the pasture), nor in 2 of the 4 years in Groups B or B+C that were not drenched and were lightly infected at the start. In the remaining 2 years Groups B or B+C were drenched once only during the course of each trial. Thus, under the conditions as in this study, little worm control is necessary, provided faecal worm egg counts are done to gauge the levels of infection before the lambs are placed on pasture, and to guard against the possibility of an increase in worm burdens thereafter in some years. Also, because of the apparent lack of carry-over between years, anthelmintic treatment at the time of introduction of the lambs or during the period of finishing should be safe as regards progressive selection for anthelmintic resistance. It is also likely to be cost-effective, considering the low cost of anthelmintics in relation to the price of lambs, to counter the possibility of a loss in production if lambs were to harbour relatively heavy worm burdens when introduced. 相似文献
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A field study was conducted to test the hypotheses that use of a combination anthelmintic and/or increasing the pool of unselected worms 'in refugia' by leaving a proportion of lambs untreated would slow the development of resistance to ivermectin. Twelve suites of four paddocks (farmlets) were seeded with a mixture of resistant and susceptible isolates of both Trichostrongylus colubriformis and Teladorsagia (Ostertagia) circumcincta calculated to yield a 95% reduction in faecal nematode egg count (FEC) after treatment with ivermectin. Each year for three years the farmlets were stocked in the spring with mobs of lambs which were treated five times at 28-day intervals with either ivermectin or an ivermectin+levamisole combination. In addition, in half the mobs the heaviest 10% of lambs remained untreated at each treatment occasion, resulting in a 2 × 2 factorial treatment structure (i.e. two drench types × two percentage treated) with three complete replicates. The development of resistance to ivermectin, and at the end to levamisole, was measured by larval development assays (LDA) and worm counts from treated and untreated tracer lambs. For T. colubriformis the development of resistance to ivermectin, as measured by tracer lamb worm burdens, was delayed by treatment with the combination and by leaving 10% of lambs untreated. In addition, the interaction between these factors approached significance (p=0.052). Similarly, results of the LDAs indicated a slower development of resistance when lambs were treated with the combination and when 10% of lambs were left untreated. For T. circumcincta, results were compromised by the rapid development of resistance, which appears to be the result of low viability in the field of the susceptible isolate used to contaminate the pastures. Although a small delay in the development of resistance to ivermectin was indicated, this was off-set by an increase in the level of resistance to levamisole. A post-study modelling experiment simulating the conditions of the field study and the starting efficacies for the two nematode species produced equivalent outputs to those measured in the field. Overall, results support the conclusions that use of combination anthelmintics and deliberately increasing 'refugia' of unselected genotypes will slow the development of anthelmintic resistance. However, as indicated in modelling studies, once resistance to all the constituent actives is well developed (efficacy<70%) the value of combinations for slowing the development of resistance is largely lost. 相似文献
16.
The ability of the nematode-killing fungus Duddingtonia flagrans to reduce number of infective larvae of three species of gastro-intestinal parasitic nematodes developing in dung was investigated in both goats and sheep. Groups of lambs and kids (12-20 weeks old) were given mono-specific infections of Haemonchus contortus, Ostertagia (Teladorsagia) circumcincta or Trichostrongylus colubriformis. Following patency of the infections (t1) faecal samples were collected for determination of faecal nematode egg count (FEC) and culture of parasite larvae. Groups of animals were then dosed on 2 consecutive days with one of the two dose rates of the fungus (250,000 or 500,000 spores/kg liveweight). One (t2) and 5 (t3) days after the second dose of fungus samples were again collected for FEC and culture. The number of larvae recovered from the faecal cultures at t1 and t3 were used as controls to assess the efficacy of the experimental treatment at t2. Average efficacy was 78% with group means ranging from 40 to 93%. Dose rate of fungus appeared to influence efficacy against O. circumcincta but not against H. contortus or T. colubriformis. Overall, there were no differences in the efficacy of the fungus against any of the parasite species or in either host animal. The results of this trial indicate the potential use of this fungus as a broad spectrum anti-parasite agent for use in both goats and sheep. 相似文献
17.
Marley CL Fraser MD Davies DA Rees ME Vale JE Forbes AB 《Veterinary parasitology》2006,142(1-2):134-141
An experiment was conducted over two successive years (2002 and 2003) to investigate the effects of grazing improved permanent pasture (mainly perennial ryegrass/white clover) by cattle or sheep, either sequentially or mixed, on the faecal egg counts and growth rates of weaned lambs when treated with anthelmintics. The grazing season was divided into two parts, May-July then July-October, relating to the pre- and post-weaning of the lambs. Four grazing regimes, replicated three times, were compared: (1) sheep only from May to October (SS); (2) cattle May to July followed by lambs until October (C/S); (3) cattle and sheep May to July followed by lambs until October (C+S/S); and (4) cattle and sheep May to July followed by cattle and lambs until October (C+S/C+S). Sward height was maintained at 6 cm using a "put and take" stocking system. At weaning, lambs were weighed and treated with an anthelmintic (0.08% ivermectin drench, Oramec) before being allocated to plots. They were then weighed and drenched every 28 days until the end of the experiment (Day 84). Faecal egg counts (FEC) were measured in all lambs immediately prior to each anthelmintic treatment. In 2002 and 2003, there were differences between the groups in FEC, with the SS lambs having the highest values and C/S lambs the lowest (P<0.01). There were also differences in the rate of liveweight gain of the lambs in each of the study years: for this parameter SS lambs had the lowest growth rate but the fastest growth was in C+S/C+S lambs not C/S lambs (P<0.01), indicating that these differences were due to factors other than parasite infection. Overall, sequential grazing of pastures with cattle then sheep reduced the faecal egg counts in lambs regularly treated with anthelmintics when compared with lambs grazing in mixed systems with cattle and sheep or with sheep only systems, however, the highest growth rates were observed in lambs in the mixed cattle/sheep grazing system throughout. 相似文献
18.
Field trials were undertaken to compare nematode population dynamics in two experimental flocks of rams selected for high and for low faecal egg counts (FECs) following two doses with 20000 infective larvae, 12000 Teladorsagia circumcincta (Tcirc) and 8000 Trichostrongylus colubriformis (Tcol) separated by a treatment. The selection was done by dosing 200 ram lambs (INRA 401 breed) and FECs proceeded with egg identification on days 28 and 35 post-each-infection. The 30 lambs with the lowest FECs constituted the group of permanent resistant rams (R), the 30 with the highest values the group of susceptible ones (S). Each group grazed separated pastures from April to November, this during 4 consecutive years. The contamination (number of eggs deposited) was estimated every 3 weeks on each pasture. The larval populations was measured by successive groups of tracer lambs. The infection of the permanent rams was done by slaughtering eight R and S rams on mid and end of each grazing season. Each autumn, new R and S ram lambs were selected to complete the R and S groups before turning out in spring. On third year, a third species (Haemonchus contortus, Hcon) was added to compare its behaviour with the two others.The regulation of parasite populations were studied by comparing what happens in R rams and pasture to S ones. The selected R ram lambs had a FEC of Tcirc 50% lower than S ones. This induced a similar lowered pasture contamination, a 25% decrease of infective larval population in years 2 and 3, and the worm burdens in R rams were the half of that in S rams after 2 years. The FEC of Tcol was 75% lower at the selection and induced similar difference in pasture contamination, but 65 and 96% reduction in L3 population, respectively, after 1 and 2 years. The worm burden was reduced by 99%. Adding Hcon species during the third year, in year 4, the L3 population was half in R pasture compared with S one, and R rams had 60% less worms of this species than S ones.This selection without any drench prevent outbreaks observed in young tracer lambs on S pasture. The comparison of selected resistant rams to selected susceptible ones and not to unselected controls gave more rapid information about the tendency of the regulation of the communities of nematode parasites. 相似文献
19.
Bisset SA Vlassoff A McMurtry LW Elliott DC Cobb RM Kieran PJ Wood IB 《New Zealand veterinary journal》1992,40(3):97-100
The efficacy of an oral formulation of the newly developed parasiticide, moxidectin, was tested against benzimidazole-resistant Haemonchus contortus, Trichostrongylus colubriformis, and Nematodirus spathiger, levamisole-resistant Ostertagia circumcincta, and susceptible Cooperia curticei infections in weaned lambs. Thirty-two lambs were experimentally infected with mixed doses of the above strains of nematodes. They were allocated into four treatment groups by stratified randomisation using liveweights and faecal egg counts 28 days later. One group received moxidectin at 0.2 mg/kg liveweight, one group oxfendazole at 4.5 mg/kg liveweight, one group levamisole at 7.5 mg/kg liveweight and the last group remained untreated as the control. Worm burdens in the lambs at slaughter 10 days after oral treatment confirmed the resistance status of the nematode strains used, and showed that moxidectin had a greater than 99.9% efficacy (p<0.01) against all of them. No adverse effects due to treatment with moxidectin were observed in any of the animals. 相似文献
20.
An experiment was completed to determine if copper oxide wire particles (COWP) had any effect on the activity of the nematode-trapping fungus Duddingtonia flagrans in growing lambs. COWP has been used recently as a dewormer in small ruminants because of nematode resistance to anthelmintics. D. flagrans has been used to control free-living stages of parasitic nematodes in livestock. Katahdin and Dorper lambs, 4 months of age, were administered no or 4 g COWP (n=24/dose) in early October 2003. Haemonchus contortus was the predominant gastrointestinal parasite during the trial, which was acquired naturally from pasture. Half the lambs from each COWP group were supplemented with corn/soybean meal with or without D. flagrans for 35 days. Fecal egg counts (FEC) and packed cell volume (PCV) were determined weekly between days 0 (day of COWP administration) and 35. Feces from lambs in each treatment group were pooled and three replicates per group were cultured for 14 days at room temperature. Larvae (L3) were identified and counted per gram of feces cultured. Treatment with COWP was effective in decreasing FEC, which remained low compared with FEC from lambs not treated with COWP. This led to an increase in PCV in these lambs (COWP x day, P<0.001). Number of larvae was decreased in feces from lambs treated with COWP and D. flagrans between days 14 and 35 compared to the other groups of lambs (COWP x D. flagrans x day, P<0.003). Percentage of larvae identified as H. contortus decreased in feces collected from lambs treated with COWP and D. flagrans between days 14 and 28 compared with other treatments (COWP x D. flagrans x day, P<0.05). Other trichostrongyles were present and remained less than 7% in feces collected from control lambs. There was no adverse effect of COWP on the ability of D. flagrans to trap residual larvae after COWP treatment. With fewer eggs being excreted due to the effect of copper on H. contortus, and the additional larval reducing effect exerted by the nematode destroying fungus D. flagrans, the expected result would be a much lower larval challenge on pasture when these two tools are used together in a sustainable control strategy. 相似文献