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1.
Suffolk, Texel, Hampshire Down and Ile de France sheep from the municipalities of Porto Amazonas, Piraquara and Araucaria in the State of Paraná, and Bagé in the State of Rio Grande do Sul were brought to Sobral, State of Ceará, to be used in a cross-breeding project. On arrival they had clinical signs of nematode parasitosis, and one Suffolk female died. The animals were treated orally with ivermectin (0.2 mg kg-1) and fifteen days later with netobimin (20.0 mg kg-1). Neither drug reduced the egg counts (measured in eggs per gram, EPG) significantly, and this suggested that the nematodes in the sheep were resistant to the anthelmintics used. Haemonchus contortus was the species involved. The egg counts were reduced after oral treatment with trichlorfon (100.0 mg kg-1). Haemonchus contortus larvae obtained from these animals before trichlorfon treatment and passaged through two nematode-free sheep were used in a further experiment. Twenty 6- to 9-month-old nematode-free lambs were infected with the H. contortus larvae (10,000 per animal) and after the infection was confirmed, were randomly divided into four groups of five animals. Group I was orally treated with ivermectin at 0.2 mg kg-1, Group II with oral netobimin at 20.0 mg kg-1, Group III with oral trichlorfon at 100.0 mg kg-1 and Group IV was a non-treated control. Egg counts and faecal cultures were taken before dosing on the day of treatment and seven days later when all animals were necropsied and the nematodes were collected from the abomasa and counted.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

2.
The broad-spectrum anthelmintic efficacy of netobimin (SCH 32481, Schering Corporation) was evaluated using 30 cross-bred spring lambs with naturally acquired infections of gastrointestinal nematodes. Three groups of 10 animals each were allotted into either control (given a tap water drench as a placebo) or 7.5 and 20 mg kg-1 dosage groups (given the netobimin as an oral drench). Seven to fourteen days post-treatment, animals were necropsied and nematodes recovered by standard techniques. Examination of fecal samples taken on dates of necropsy showed median egg production was reduced in treated animals (61.98% with 7.5 mg kg-1 and 100% with 20 mg kg-1). The compound was highly effective in removal of adult nematodes representing a number of genera and species of trichostrongyloids at the 7.5 and 20 mg kg-1 dose levels (shown, respectively, below). These included Ostertagia spp., with O. circumcincta, O. trifurcata, O. ostertagi and Teladorsagia davtiani (96.20%; 100%), Trichostrongylus spp., with T. axei, T. vitrinus and T. colubriformis (100%; 98.72%), Nematodirus spp., with N. spathiger, N. filicollis and N. battus (100% both levels) and Haemonchus contortus (100% both levels). High efficacies against other species of nematodes (at both dose levels) were not statistically significant (Cooperia spp., Chabertia ovina and Oesophagostomum venulosum). At 20 mg kg-1, netobimin significantly reduced populations of early and late fourth stage larvae of Ostertagia spp. by 100%. The overall efficacy (all life stages included) was 90.16% at 7.5 mg kg-1 and 98.77% at 20 mg kg-1 dose levels. No adverse reactions or signs of toxicosis were observed.  相似文献   

3.
The potential of the chitin synthesis inhibitor diflubenzuron (DFB) to alter the development of the parasitic nematodes (Ascaris suum and Haemonchus contortus was investigated. DFB given orally (10 mg kg-1 per day for 30 days) to sheep inoculated with H. contortus infective larvae did not prevent the establishment of adults or affect fecal egg output. However, there was a significant (greater than 90%) decrease in the number of infective larvae recovered from fecal cultures derived from lambs harboring H. contortus adults that were treated with DFB. DFB did not affect egg hatching. Oral administration (10 mg kg-1 per day for 20 days) of DFB to swine harboring adult A. suum adults had no effect on the adult worm burden or on egg morphology, but eggs removed from worms obtained from DFB-treated swine contained less chitin than eggs removed from untreated control swine. DFB also inhibited chitin synthesis in vitro in the isolated reproductive tract of A. suum adults. These results indicate that DFB at high doses can inhibit the subsequent development of H. contortus larvae in the feces. Since H. contortus larvae lack chitin, DFB may act on these larvae by a mechanism independent of a direct effect on chitin synthesis.  相似文献   

4.
The effect of ivermectin delivered from a sustained-release bolus (I-SRB) on the weight gain of beef cattle through a grazing season was evaluated using 20 yearling beef steer calves randomly divided into two groups of ten animals each. Calves in the control group each received a placebo bolus, while those in the treatment group each received an I-SRB designed to release 12 mg ivermectin day-1 for approximately 90 days. All animals were weighted and samples of feces were collected from the rectum at monthly intervals, beginning on Day 0, until trial termination (Day 148). Pasture larval counts were also conducted on herbage collected on each sampling date. On Day 119, two control and two treated calves were removed from pasture, housed in isolation for 3 weeks, then necropsied for recovery of gastrointestinal nematodes. Three sets of parasite-naive tracer calves were utilized to evaluate the initial, interim and final levels of pasture contamination by nematode larvae. A fourth set was used to evaluate the level of pasture contamination the following spring. The use of the I-SRB resulted in a greater than 99% reduction in fecal egg counts of trichostrongyles and numbers of gastrointestinal nematodes in the treated principals, as well as an average daily gain advantage of 0.114 kg over the 148 day period. A 67-98% reduction in pasture larval nematode contamination occurred on pastures grazed by the treated animals, as indicated by the parasite burden in tracer calves and pasture larval counts. The treatment effect was eventually lost by the following spring since tracer calves on the treated pasture had only 33% fewer nematodes than those on the control pasture.  相似文献   

5.
Previous studies showed that Santa Ines (SI) hair sheep were more resistant to gastrointestinal nematode infections (GIN) than Ile de France (IF) sheep. The present experiment aimed to evaluate if that reported resistance difference against GIN also occurred against Oestrus ovis infestation and also to evaluate the influence of O. ovis infestation on the gastrointestinal nematodes (GIN) infections. SI (n=12) and IF (n=12) young male lambs were weaned at 2 months of age and moved to a paddock (0.3 ha) with Brachiaria decumbens grass, where they also received concentrate ration. The animals were kept together during the experimental period (September to early December 2009). Fecal and blood samples were taken from all animals every 2 weeks and body weight and nasal discharge score (oestrosis clinic signs) were recorded on the same occasion. In early December 2009, all lambs were sacrificed and O. ovis larvae and GIN were recovered, counted and identified according to the larval stage. All animals were infested by different larval instars of O. ovis without any statistical difference between breeds (P>0.05). The SI lambs had an average of 24.8 larvae, and the intensity of infection ranged between 14 and 39 larvae, while the IF lambs showed an average of 23.5 larvae with the minimum and maximum from 11 to 36 larvae, respectively. SI lambs presented the lowest nematode fecal egg counts (FECs) and the lowest mean numbers of Haemonchus contortus, Trichostrongylus colubriformis and Strongyloides papillosus, however, there was no significant differences between group means (P>0.05). Inverse relationship between numbers of O. ovis larvae and gastrointestinal nematodes was observed in both breeds. SI sheep showed a significant increase in blood eosinophils and total IgE serum levels and these variables were negatively correlated with nematode FEC. A negative correlation was observed between total IgE serum level and H. contortus burden in both breeds. In conclusion, there was no breed difference regarding O. ovis infestation and in each breed, animals with more nasal bot fly larvae tended to display smaller worm burden.  相似文献   

6.
A mixed population of Haemonchus contortus, Teladorsagia circumcincta and Trichostrongylus colubriformis was passed for four generations through lambs. In successive passages and on Day 6 (D6), lambs were dosed subcutaneously with ivermectin at 100, 200, 250 and 225 micrograms kg-1 body weight, respectively. No larvae of H. contortus were recovered after the first passage and following the third drug exposure only T. colubriformis was present. Larvae of the selected strain of T. colubriformis developed to third stage, sheathed larvae in vitro in concentrations of ivermectin that inhibited development of larvae from the original strain of T. colubriformis. A definitive control test was then run with 45 lambs, to compare this selected strain to the original strain. The treatments were 150 micrograms kg-1 subcutaneous (SC) D6, 200 micrograms kg-1 SC D6, 200 micrograms kg-1 intraruminal (IR) D6 and 200 micrograms kg-1 SC D21; all treatments were compared to non-treated controls, selected or original strain as applicable. The D6 IR and D6 SC 150 micrograms kg-1 treatments were greater than 99% effective in both strains, although the D6 SC 200 micrograms kg-1 treatment was 85 and 48% effective in the original and selected strain, respectively. The D21 200 micrograms kg-1 was only 58% effective against the selected strain. There was significant (P less than 0.001) differences between the original and selected strains of T. colubriformis for both fecal egg output and worm counts. The exposure of four generations of immature T. colubriformis to ivermectin selected for partial resistance.  相似文献   

7.
Eighty-four 10-week-old lambs were used to investigate the effect of copper oxide wire particle treatment on the establishment of major gastrointestinal nematodes. They were maintained on pasture previously treated to minimise larval contamination. Five grams of uniform sized copper oxide wire particles were given orally five days before infection with either 20,000 Trichostrongylus colubriformis larvae, 20,000 Ostertagia circumcincta larvae or 3000 Haemonchus contortus larvae given as three doses at three-day intervals. The animals were slaughtered 21 or 22 days after the last infective dose. Parasite burdens in the lambs treated with copper oxide wire particles were reduced by 96 per cent in the case of H contortus and by 56 per cent in the case of O circumcincta compared to burdens in controls. There was no significant effect of copper particles on the establishment of T colubriformis.  相似文献   

8.
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   

9.
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.  相似文献   

10.
Twelve calves (mean weight, 175.5 kg) were used to confirm efficacy of ivermectin delivered from a prototype sustained-release bolus against naturally acquired gastrointestinal nematodes including early fourth-stage (inhibited) larvae of Ostertagia ostertagi. The calves were allocated by restricted randomization on weight to 1 of 2 groups: controls, to which a placebo bolus was given orally, and treated calves, to which a sustained-release bolus designed to deliver 8 mg of ivermectin/day at a steady rate was given orally. After treatment, the 2 groups were housed in separate pens with concrete flooring. Twenty-eight days after treatment, all calves were euthanatized and necropsied. The ivermectin-treated calves had no larval or adult Ostertagia spp and significantly (P less than 0.01) fewer adult Trichostrongylus axei and adult Cooperia (C oncophora, C punctata and C surnabada) than control calves. Efficacy of ivermectin was greater than 99% for Cooperia spp, and 100% for other parasites. Drug-related adverse reactions were not observed.  相似文献   

11.
An experiment was conducted to examine the influence of dietary protein on parasite establishment and pathogenesis of Haemonchus contortus in lambs of two breeds. Finn Dorset and Scottish Blackface. The lambs were introduced to high protein (170 g crude protein (CP) kg-1 dry matter (DM) or low protein (88 g CP kg-1 DM) diets at three months old and infected one month later with 125 larvae (kg bodyweight)-1. Blood and faecal samples were collected for analysis and bodyweights recorded weekly. The lambs were killed 20 weeks after infection. A second experiment was conducted in Blackface lambs solely to determine the influence on parasite establishment of the high and low protein diets following infection with 125 larvae kg-1. These lambs were killed five or 14 weeks after infection. Results showed that in Scottish Blackface lambs dietary protein did not significantly influence the establishment of H contortus. However, in Finn Dorset lambs dietary protein may have influenced parasite establishment since lambs on the low protein diet had a higher faecal egg output four weeks after infection and more severe clinical signs than infected lambs of the same breed on a high protein diet.  相似文献   

12.
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.  相似文献   

13.
An investigation into the population dynamics of sheep nematodes was carried out between April 1970 and September 1971. Faecal egg counts were made from both ewes and lambs at weeks intervals while grass samples were taken fortnightly throughout the summer and monthly during the winter. From these results absolute numbers of nematode eggs and infective larvae were estimated and these figures used as a basis for determining the level of mortality occurring during development from egg to infective larva. The figures were also used to assess the relative importance of the ewe 'spring rise' and the egg output of the lambs in June while grazing contaminated pasture. These calculations suggest that larval mortality was very high and that it may vary considerably from year to year depending upon the climatic conditions prevailing. There was also an indication that the ewe 'spring rise' was the major source of the wave of infection which occurs in the lambs in late August and September.  相似文献   

14.
Twenty helminth-free lambs were fed diets containing either 169 g crude protein (CP) kg-1 dry matter (DM) or 88 g CP kg-1 DM from the age of seven months. One month later five lambs from each dietary group were vaccinated against Haemonchus contortus by the oral administration of 10,000 irradiated larvae on two occasions, four weeks apart. Four weeks following the administration of the second dose of irradiated larvae both the vaccinated and unvaccinated lambs were exposed to an experimental infection of 10,000 non-irradiated H contortus larvae Faecal egg output and haematological changes were monitored throughout the study. The lambs were slaughtered 28 days after challenge when worm burdens were assessed. Vaccination was equally successful in inducing a strong resistance to the challenge infection regardless of dietary status. It was concluded that dietary protein does not influence the response to vaccination with irradiated H contortus larvae of lambs more than seven months old.  相似文献   

15.
Epidemiological control of nematodes in weaned lambs in New England was investigated over three grazing seasons (n = 58, n = 52 and n = 62 lambs, respectively). Spring prophylactic treatment, clean pasture and mid-summer treat-and-move to hayfield strategies were compared to traditional fall treatments (control). In these studies when lambs were weaned prior to grazing, the most abundant nematodes were Nematodirus sp. Under these conditions, where only low levels of Haemonchus contortus were present, no significant improvement in body weight gain was observed for the epidemiologic approaches compared to the traditional fall treatments. No untreated control was used, and fecal egg counts and pasture larval counts indicate low total worm burdens with a controllable fall rise in pasture infectivity. These results indicate the importance of hypobiosis for the survival of H. contortus and suggest that weaning lambs prior to grazing can be an effective epidemiological control practice.  相似文献   

16.
A study was conducted over 3 years (1998-2000) to investigate larval availability of gastrointestinal nematodes from faeces of cattle reared under different parasite control schemes. These cattle were part of a parallel, but separate grazing trial, and were used as donor animals for the faecal material used in this experiment. At monthly intervals, faeces were collected and pooled from three groups of first-season grazing cattle. These groups were either untreated, ivermectin bolus treated or fed the nematophagous fungus Duddingtonia flagrans. The untreated and fungus treated animals were infected with gastrointestinal nematodes and the number of eggs per gram (epg) pooled faeces ranged between 50 and 700 in the untreated group and between 25 and 525 epg in the fungus treated group. Each year between June and September, artificial 1 kg dung pats were prepared and deposited on pasture and protected from birds. The same treatments, deposition times and locations were repeated throughout the study. Larval recovery from herbage of an entire circular area surrounding the dung pats was made in a sequential fashion. This was achieved by clipping samples in replicate 1/4 sectors around the dung pats 4, 6, 8 and 10 weeks after deposition. In addition, coinciding with the usual time of livestock turn-out in early May of the following year, grass samples were taken from a circular area centred where the dung pats had been located to estimate the number of overwintered larvae, which had not been harvested during the intensive grass sampling the previous year. It was found that recovery and number of infective larvae varied considerably within and between seasons. Although the faecal egg counts in 1999 never exceeded 300 epg of the faecal pats derived from the untreated animals, the abnormally dry conditions of this year generated the highest level of overwintered larvae found on herbage in early May 2000, for the 3 years of the study. Overall, biological control with D. flagrans significantly reduced larval availability on herbage, both during and between the grazing seasons, when compared with the untreated control. However, the fungus did not significantly reduce overwintered larvae derived from early season depositions (June and July), particularly when dung pats disappeared within 2 weeks after deposition. Very low number of larvae (<3 per kg dry herbage) were sporadically recovered from grass samples surrounding the ivermectin bolus faecal pats.  相似文献   

17.
A comparison is made between the resistance conferred to Haemonchus contortus challenge by irradiated larval treatment and transfer factor (TF) treatment in four-month-old lambs and seven-month-old lambs. As in previous investigations the irradiated larval treatment failed to confer resistance to the four-month-old lambs challenged with 10,000 third stage larvae while similar irradiated larval treatment in seven-month-old lambs reduced the worm burdens by 40 per cent compared to controls. The TF treatment produced a 34 per cent reduction in the challenge infection in the four-month-old lambs and a 45 per cent reduction in the seven-month-old lambs compared to the control lambs. It is concluded that TF activity operates independently of immune competence.  相似文献   

18.
The reindeer husbandry range of Scandinavia overlaps with sheep, goat, and cattle pastures. The aim of this study was to determine whether reindeer are suitable hosts for ovine or bovine nematode parasites, and thus may spread these parasites into the reindeer husbandry regions. To render worm-free, twelve 4-month-old male reindeer calves, six lambs, and six bovine calves were given ivermectin at 200 microg/kg body weight. Five weeks post-treatment, six reindeer calves were each artificially dosed with 10,000 third-stage larvae (L3) of gastrointestinal nematodes derived from sheep, and an additional six reindeer with L3 derived from cattle. Lambs and bovine calves received the same dose of ovine and bovine larvae as reindeer, from the same larval source, respectively. Faecal samples collected on five occasions after the larval dosing revealed that by the fourth week, all reindeer calves, lambs, and bovine calves were infected. Animals were slaughtered on days 40 (reindeer) or 47 (lambs and bovine calves) after the larval dosing. Reindeer calves were most susceptible to L3 derived from sheep. The overall mean intensity of Haemochus contortus, Trichostrongylus axei, and Teladorsagia circumcincta, did not differ between reindeer and sheep; however, early fourth-stage larvae of H. contortus were more abundant in reindeer (p = 0.002). The establishment of bovine-derived Ostertagia ostertagi was similar in reindeer (62%) and bovine calves (57%), but larval inhibition was much higher in reindeer (91%, p < 0.001) than in cattle (31%). Very poor establishment of bovine derived Cooperia oncophora was recorded in reindeer calves (2%) compared with bovine calves (59%). These results show that young reindeer are susceptible hosts to the important gastrointestinal parasites of sheep (T. circumcincta, H. contortus) and cattle (O. ostertagi), as well as being a suitable host for T. axei.  相似文献   

19.
Groups of 10 three-and-a-half-month-old Suffolkcross lambs were infected daily, five times a week, for 12 weeks with either zero, 500, 1500, 3000 or 5000 larvae of Ostertagia circumcincta and grazed together on a series of 'clean' paddocks. All the lambs were moved at seven to 10 day intervals to a fresh paddock to prevent autoinfection and were killed after 14 weeks. Another group was killed at the outset as a control for carcase analysis. Mean O circumcincta populations were 34 (grazing control) and 1224, 473, 1092 and 4331 for the groups receiving 500, 1500, 3000 and 5000 larvae per day respectively. The percentage of fourth stage larvae increased with increasing larval intake. Extensive abomasal damage with mucosal hypertrophy and depletion of parietal cells occurred in the lambs receiving 3000 and 5000 O circumcincta larvae per day. Intakes of 1500 larvae per day and above depressed growth rate by 24 to 37 per cent, reduced the deposition of protein in the carcase by 34 to 52 per cent and lowered calcium/phosphorus deposition by 23 to 48 per cent. Plasma pepsinogen concentrations were consistently elevated in lambs receiving 3000 or 5000 larvae per day and may be a useful aid to recognising abomasal damage sufficient to affect productivity.  相似文献   

20.
Following evidence of reduced efficacy of ivermectin in a field population of Haemonchus contortus in Brazil, this strain of the parasite was submitted to a controlled anthelmintic test. Eighty worm-free lambs were randomly split into two groups of 40. Each lamb in the first group was infected with 5000 third stage larvae (L3) of the ivermectin-resistant strain; the remaining 40 lambs were each infected with 5000 L3 of a H. contortus strain of known susceptibility to the major groups of anthelmintic compounds used in sheep. On Day 28 post-infection, each group was subdivided according to egg counts and at random into four sub-groups of ten lambs, each of which was treated with albendazole (ABZ) at 3.8 mg kg-1, levamisole (LEV) at 7.5 mg kg-1 or ivermectin (IVM) at 0.2 mg kg-1, or was left as untreated control. At slaughter, 7 days later, all the anthelmintics reduced worm burdens in animals infected with the susceptible strain (ABZ 98.9%, LEV and IVM 100%). By contrast, in the lambs infected with the ivermectin-resistant strain, LEV was 99.8% effective, but ABZ reduced worm counts by only 14.7% and IVM by only 10.4%. Interestingly at necropsy on Day 7 post-treatment, the egg counts in the resistant strain treated with ABZ had been reduced by 92.5%, although worm counts were reduced by only 14.7%.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

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