首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Three experiments were conducted to investigate experimentally the occurrence of periparturient nematode egg rise in ewes and the hormonal modulation of Haemonchus contortus infections. In the first experiment, fall-bred and winter-bred pregnant (n = 4 and 14, respectively) and nonpregnant (n = 5 and 29, respectively) ewes were treated with anthelmintic and were pastured together on fields that were contaminated with H contortus. Three weeks before lambing, all ewes were placed in concrete pens; fecal egg counts for the winter-bred group were obtained on alternate days. Pregnant and lactating ewes had significantly larger numbers (P less than 0.01) of H contortus eggs than did the nonpregnant controls 1 week before and after lambing. Lactating, fall-bred ewes had significantly (P less than 0.01) more adult worms in their abomasum through natural acquisition than the nonpregnant controls. In the second experiment, fall-bred and winter-bred, helminth-free, pregnant (n = 4 and 8, respectively) and nonpregnant (n = 3 and 15, respectively) ewes were inoculated on 5 alternate days, beginning 70 days after breeding with 20,000 infective H contortus larvae. The ewes were maintained on concrete pens throughout pregnancy. Fecal egg counts were significantly (P less than 0.05) greater in pregnant ewes, beginning 1 week before lambing until 1 week after lambing. Abomasums of lactating ewes from both lambing seasons yielded significantly (P less than 0.01) more adult worms at necropsy than nonpregnant ewes. In the third experiment, ewes were ovariectomized (n = 15) or sham-operated (n = 9); half of the control ewes were bred.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

2.
In May 2002, studies on the seasonal patterns of nematode infection of sheep were undertaken on four commercial sheep farms in southern Sweden, which had previously reported problems with nematode parasitism, especially due to Haemonchus contortus. One farm was used for intensive investigation. This entailed the establishment of two replicate groups of sheep, each consisting of 20 ewes and their lambs, on adjacent pasture paddocks. The seasonal patterns of nematode infection were followed by regular (approximately monthly) sampling of both ewes and lambs for nematode faecal egg counts and larval differentiation, and the sequential use of replicate groups of tracer lambs. H. contortus and Teladorsagia circumcincta were the most abundant nematode species, with the former most prevalent in the post-parturient faecal egg counts of ewes. Tracer worm counts showed almost 100% arrested development in the early fourth larval stage for H. contortus as early as mid-summer and the numbers of parasites progressively increased during the season. T. circumcincta also showed high levels of arrested development, but not as early, or as absolute, as for H. contortus. Tracers allocated to the paddocks at the time of turn-out following winter in May 2003, showed virtually a total absence of H. contortus in contrast to exceedingly high infections with T. circumcincta. Results of the three additional monitoring flocks supported these findings. It can be concluded that under Swedish sheep farming conditions, H. contortus has evolved to survive the long, cold winters entirely within the host as the arrested larval stage, relying on the lambing ewe to complete its life cycle. The peri-parturient relaxation of resistance in the ewes triggers the resumption of development to the adult egg-laying parasites to result in pasture contamination and the completion of just one parasite generation/year. In contrast, T. circumcincta can survive well over-winter, both on pasture and within the host.  相似文献   

3.
Worm egg counts of yearling Angora or Merino wethers grazing in mixed flocks at either 4/ha or 8/ha were observed over a 5 month period. Based on faecal egg counts infection levels in the sheep increased for the first 3 months and then decreased as the animals developed resistance. Egg counts in the goats did not decrease during the experiment. Post mortem worm counts indicated that there was a significant host species--stocking rate interaction on worm burdens of Haemonchus contortus adults and Ostertagia circumcincta adults and larvae. Goats had more H. contortus and O. circumcincta adults than sheep at the 8/ha stocking rate. At 4/ha goats had fewer O. circumcincta fourth stage larvae than sheep. There was no stocking rate effect on the numbers of Trichostrongylus axei or T. colubriformis. Sheep had more T. axei and fewer T. colubriformis than goats.  相似文献   

4.
Three-year-old, non-lactating and non-pregnant Merino ewes, raised on pasture under a program of strategic treatment with anthelmintic and found to be extremely resistant to "trickle" infection with Haemonchus contortus, were given single-dose infections with either H. contortus or Trichostrongylus colubriformis or both species together. The purpose was to ascertain the intensity of protective immunity against the 2 parasites in sheep with immunity acquired from a presumably slight exposure to infection. To provide a criterion, some infected ewes were immunosuppressed with corticosteroid, dexamethasone. Untreated ewes were extremely resistant to challenge infection with either 15,000 or 150,000 H. contortus or 15,000 T. colubriformis. Surprisingly, when mixed infection was given, egg counts for H. contortus were significantly elevated compared with infection by that species alone. Antibody to antigens from infective larval and adult H. contortus was measured in serum by enzyme-linked-immunosorbent assay (ELISA) during the course of infection. Serum titres against larval antigens were significantly depressed when infections with either H. contortus or T. colubriformis were permitted by immunosuppression with dexamethasone, whereas those against adult antigen were depressed when infection with T. colubriformis was permitted.  相似文献   

5.
Compared to INRA 401 lambs reared in France, Black Belly (BB) lambs reared in Guadeloupe (F.W.I.) were highly resistant to both primary and secondary experimental infection with Haemonchus contortus. To investigate this huge inter-breed difference, a nucleus flock of BB was constituted, and experiments were conducted to: (i) confirm this difference in lambs born in France, (ii) check whether it was similar for Trichostrongylus colubriformis and Teladorsagia circumcincta, and (iii) find out whether this difference was age-related. Forty BB lambs, 84 F1 lambs (BB siresxINRA 401 ewes) and 88 INRA 401 lambs born in two cohorts were used in an experimental design involving three host breeds, both genders and two age-groups (3.5- and 7-month-old when first infected). The limited availability of BB lambs made the study incomplete. Infection consisted of the administration of two doses of 10,000 infective larvae of one of the nematode species, separated by an anthelmintic treatment and an interval of 1 week before the second dose was administered. Fecal egg counts (FECs) were done on Days 28 and 35 after each infection; ewe lambs of the INRA 401 and F1 breeds were necropsied, the worm burden was established, the length of the female worms measured and the eggs in utero counted. For H. contortus and T. colubriformis, the FEC was lower in the BB than in the INRA 401 lambs, and the FEC found for the F1 lambs was intermediate. For T. circumcincta, only data for the F1 and INRA 401 lambs were available, and the FECs for these breeds were the same. In all three breeds, the FEC determined after the second dose was significantly lower than that found after the first dose in the ewe lambs, but not in the ram lambs. Infecting the lambs when they were 7- instead of 3.5-month-old significantly lowered egg excretion of both parasites in the F1 (P<0.0001), but not the INRA 401 lambs. Worm numbers in the F1 and in the INRA 401 ewe lambs confirmed the FEC data, many F1 lambs being free of T. colubriformis. The H. contortus female worms were shorter and had fewer eggs in utero in the F1 than in the INRA 401 lambs. A higher proportion of T. circumcincta was at the fourth larval stage in the F1 lambs. In conclusion, the BB breed is much more resistant than INRA 401 to H. contortus, with the F1 lambs being more like the BBs after the second dose. This difference was also found for T. colubriformis and, to a lesser extent, for T. circumcincta.  相似文献   

6.
The relationship between anti-parasite IgA antibody levels in plasma and the periparturient egg rise in sheep was investigated. Ostertagia circumcincta larvae (5000 third stage larvae three times weekly) were administered to three groups of seven adult immune ewes from 12 weeks before until three weeks after lambing (group 1) or from six (group 2) or 14 (group 3) weeks before until three weeks before lambing. Seven additional ewes were not challenged (group 4 controls). Ewes in groups 1, 2 and 4 received anthelmintics 14 weeks before lambing. Challenge of the pregnant ewes with O circumcincta larvae resulted in substantial increases in faecal egg counts only during the periparturient period regardless of the larval dosing regimen. Furthermore, the periparturient rise in faecal egg counts was closely associated with a significant increase in anti-parasite IgA antibody levels in plasma. This rise in IgA antibody levels occurred at a time when IgA is transported from the gut to milk during early lactation. It is postulated that this may lead to a temporary reduction in abomasal antibody levels of ewes and hence permit the establishment of larvae and, or, the emergence and development of inhibited larvae and thereby lead to the periparturient rise in faecal egg count.  相似文献   

7.
The seasonal changes in nematode populations of a flock of sheep in the Montreal area were determined using serial fecal egg counts, fecal culture of larvae and necropsy worm counts. It was found that Ostertagia spp.,Nematodirus spp., Trichostrongylus agei, Trichostrongylus spp. and Chabertia ovina over-wintered on pasture and could initiate patent infections the following spring. The development of populations of H. contortus was typical of that seen with most of the other species and was characterized by the following series of events. In early winter when the study was started with stabled pregnant ewes, most of the populations were immature and the egg counts were low and remained so throughout the entire winter. However, in the spring, following lambing, large numbers of adult worms were seen with a consequent decrease in immatures and a sudden increase in egg counts. When the ewes and lambs were pastured together, the egg counts in ewes dropped consequent to “self-cure”, the “spring-rise” providing the major source of overwhelming infections for lambs with deaths by the end of July. As the season progressed larvae taken in by both ewes and lambs did not mature, and by early fall, most of the worm population consisted of immature forms. It appeared that H. contortus could not have more than two generations in ewes or lambs in a single grazing season.  相似文献   

8.
The effects of tannins on adult populations of Haemonchus contortus, Trichostrongylus colubriformis and Teladorsagia circumcincta in goats are characterised mainly by a decrease in egg excretion without any significant changes in worm number. In contrast, the impact of tannins on T. colubriformis or T. circumcincta third-stage larvae (L3) is associated with a significant reduction in worm establishment. The objective of the present study was to examine the effects of quebracho extract tannins on H. contortus L3. The consequences of consumption of sainfoin hay were also examined. Twenty-one na?ve kids were divided into three experimental groups. Group Q received quebracho extract and group S received sainfoin hay from days D3 to D5. Group C remained as an infected control group. All kids received 1500 L3 H. contortus on D0, D1 and D2. On D18, post-infection, the kids were slaughtered and the worm populations compared in the different groups. Compared to the control values, the worm counts decreased, respectively, by 33% and 38% in groups Q and S but the differences were not significant. No differences were found in pathophysiological measurements between the three groups. The results confirm differences in tannin effect according to nematode species but not parasitic stage.  相似文献   

9.
The nematode egg output of two groups of ewes, a pregnant test group (2-3 years of age) mated between March and April and a non-pregnant control group (5-6 years of age) was followed. The worm burdens acquired by worm-free 'tracer' lambs were also followed on the same pasture from March 1988 to February 1989. There was a significant difference (P less than 0.05) in the magnitude of the egg output in the test group compared with the control group. In the test ewes, an initial rise in egg production occurred 2 weeks after lambing and was maintained for five consecutive months. Necropsy worm counts from the 'tracer' lambs revealed that pasture larval levels were directly related to the levels of rainfall. Adult nematodes (Trichostrongylus colubriformis, Trichostrongylus axei, Haemonchus contortus, Oesophagostomum venulosum and Trichuris ovis), and some Moniezia expansa were present in almost all the lambs throughout the year, with the exception of January and February 1989. The absence of immature larvae in these lambs indicates that arrested development is not a feature of the life cycle of these species in Southern Ghana. The occurrence of a periparturient rise of nematode eggs in West African Dwarf ewes, a year-round breeder, means that susceptible lambs could be open to infection throughout the year. Control should, therefore, be conducted by treating ewes after lambing and restricting the breeding season to particular periods of the year.  相似文献   

10.
Nineteen ewes maintained under 'worm-free' conditions received anthelmintic and 1 week later were dosed on 5 days each week with 500 Teladorsagia circumcincta larvae for between 10 and 12.5 weeks. Faecal egg counts were determined twice weekly. There were three groups: pregnant (P) ewes (n = 6) which each reared twin lambs, hormone-treated (H) ewes (n = 7) which were not pregnant and were given exogenous hormones (dexamethasone, oestradiol-17 beta, progesterone) for 37 days to induce udder development and milk production, and untreated barren (B) ewes (n = 6). The plasma concentrations of oestradiol-17 beta, prolactin and progesterone were measured. Starting 10-15 days before birth in Group P, there was a biphasic periparturient rise in egg count and the onset of the first peak in egg count preceded the parturient peak in plasma prolactin concentration by several days. Most Group H (5/7) and all Group B ewes remained highly resistant to Teladorsagia infection throughout, despite an induced rise in prolactin concentrations in Group H ewes. It was concluded that factors other than prolactin initiate the periparturient rise but that prolactin is one factor which maintains the response once lactation commences.  相似文献   

11.
AIM: To confirm the presence of multiple anthelmintic resistance on a sheep farm in New Zealand. METHODS: Three groups of 10 weaned Romney-cross lambs were treated either with an oral dose of ivermectin (0.2 mg/kg), or a benzimidazole/levamisole (BZ/LEV) combination (4.75 albendazole and 7.5 mg/kg levamisole), or were left untreated. Ten days later, animals were necropsied, and adult worms recovered and identified from the abomasa and small intestines. Pre- and post-treatment faecal nematode egg counts (FEC) were recorded, and larval cultures were performed. RESULTS: In a faecal egg count reduction test (FECRT), adjusted to reflect pre- and post-treatment larval culture results, ivermectin resistance was detected in Teladorsagia (Ostertagia), Trichostrongylus and Haemonchus spp, while BZ/LEV combination- resistant Teladorsagia and Trichostrongylus spp were also present. Adult worm counts confirmed these results, and identified the species involved as Teladorsagia circumcincta, Trichostrongylus colubriformis and H. contortus. CONCLUSION: Multiple, multi-generic anthelmintic resistance was confirmed on a sheep property in New Zealand. This included the first confirmed case of ivermectin resistance in T. colubriformis from sheep in New Zealand.  相似文献   

12.
Studies on the epidemiology of gastrointestinal nematodes of sheep, conducted at two different farms in the Baghdad area, in 1979, revealed two peaks in worm egg counts in ewes, one in spring and the other in autumn; the latter coincided with the lambing season. Similarly in lambs, two peaks of infection were apparent, but the spring peak was not so well defined. During the hot and dry summer months of Iraq, helminthic infection was at a low level. Faecal culture for larvae and their identification indicated the predominance of Haemonchus contortus infection in the ewes and that of Ostertagia and Trichostrongylus spp. in the lambs examined, Trichostrongylus infection predominating during the hot, dry period of the year. The self-cure phenomenon as well as preparturient rise in egg counts, as reported in other countries, was also observed during this study.  相似文献   

13.
Weight gain costs due to infection were higher in sheep than goats, 28 and 17.5%, respectively, for Trichostrongylus colubriformis and 48.7 and 32.2%, respectively, for Haemonchus contortus. The extent of bodyweight cost attributed to anorexia in sheep infected with H. contortus was higher (13.5 g/day) than in sheep infected with T. colubriformis (2.3 g/day). On the other hand, bodyweight cost due to the other pathogenic effects in sheep infected with T. colubriformis were higher (35.6 g/day) compared to sheep infected with H. contortus (10.9 g/day). A strong relationship between faecal egg count and worm count (r=0.79, P=0.006) was shown only in sheep infected with T. colubriformis. About half of the infected sheep and goats had low or zero faecal egg counts throughout the study. In about 40% the egg count rose initially but became low by weeks 10-16, whereas in about 10% counts increased progressively throughout the period of observation and these animals also had the highest numbers of worms at slaughter. Packed cell volume was reduced in sheep and goats infected with H. contortus but serum protein and haemoglobin levels were unaffected. Sheep infected with T. colubriformis had a higher level of eosinophilia after 8 weeks (18.4%) than sheep infected with H. contortus (11.4%), whereas this pattern was reversed in goats and levels were also lower (4.1 and 8.9%, respectively). There was no apparent relationship between eosinophilia and resistance to infection with H. contortus or T. colubriformis.  相似文献   

14.
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   

15.
The involvement of prolactin in the periparturient rise in the faecal nematode egg count in sheep was investigated. Ostertagia circumcincta larvae (5000 third stage larvae three times weekly) were administered to adult immune ewes from three weeks before parturition to three weeks afterwards. Ten ewes were injected twice daily with 2-bromo-alpha-ergocryptine (bromocriptine), an antagonist of prolactin secretion, for two weeks starting two days after lambing while 10 ewes remained untreated. Bromocriptine treatment was initiated approximately two weeks pre partum in three other ewes. Plasma pepsinogen concentrations rose significantly by one week after the start of O circumcincta larval challenge in all the ewes but faecal egg counts remained negative until approximately one week post partum. Plasma prolactin concentration was reduced to a very low level in all bromocriptine treated ewes but this did not alter the dynamics of the periparturient rise in faecal egg counts. Neither cell-mediated nor humoral immunity of the ewes, as assessed by their sensitivity to BCG inoculation and by antibody titre raised against horse red blood cells, respectively, were impaired during the rise in faecal egg count, nor were these parameters altered by manipulation of plasma prolactin concentration. Lamb growth rate was not retarded by low plasma prolactin concentration in the bromocriptine treated ewes. These results are not consistent with the generally held hypothesis that elevated plasma prolactin concentration is directly associated with the periparturient rise.  相似文献   

16.
OBJECTIVE; To show that low bodyweight is a predisposing cause of high Trichostrongylus colubriformis and Haemonchus contortus burdens and egg counts in Merino lambs. DESIGN: A comparison was made, among lambs of different bodyweights, on the effect on immunity of a primary or secondary viable infection with T colubriformis or H contortus larvae. PROCEDURE: Sixty-one Merino lambs, 1 or 6 months of age, were penned indoors and given primary, or both primary and secondary, infection of T colubriformis or H contortus. Faecal egg counts, worm counts and parasite-specific immunoglobulin concentrations were examined for their relationships with bodyweight. RESULTS: Bodyweight at the start of a primary infection was correlated with worm burden, worm fecundity and jejunal IgA antibody concentration. Merino lambs weighing less than 23 kg at the time of first exposure to T colubriformis or H contortus had impaired ability to develop protective mucosal immunity and to resist homologous challenge. CONCLUSION: If the goal is to ensure that lambs develop immunity before weaning, then every endeavour should be made to achieve the combination of critical bodyweight and exposure to moderate levels of nematode infection as soon as possible.  相似文献   

17.
One of three groups of sheep was challenged twice-weekly with infective-stage larvae (L3) of the sheep parasite O. circumcincta, another with the cattle parasite O. ostertagi while the third received no larval challenge. Positive faecal egg counts (FEC) and a rise in plasma pepsinogen levels were observed only in those animals given O. circumcincta. Anti-O. circumcincta L3 IgG titres were rapidly elevated during parasite challenge with either O. circumcincta or O. ostertagi. Throughout the experiment, no rise in anti-adult IgG titres or eosinophil numbers was observed in peripheral blood in any group. On evidence of self-cure of the trickle-infection, determined by a reduction in FEC, all groups were drenched and challenged with 15,000 O. circumcincta L3. No effect of previous challenge on parasite establishment or FEC was observed, although egg viability was significantly reduced in both groups given prior challenge. Significant differences in adult female worm length were observed between groups. Those recovered from animals previously challenged with O. circumcincta were shorter than from those given O. ostertagi which were in turn shorter than those from previously unchallenged animals. In utero egg counts were significantly lower in worms from animals previously challenged with O. circumcincta than in those from unchallenged control animals. The results indicate that a level of immunity to O. circumcincta can be conferred by exposure to O. ostertagi.  相似文献   

18.
Two experiments were conducted to elucidate the timing and nature of the sheep immune response to Haemonchus contortus (Barber's pole worm). The first experiment examined the establishment of H. contortus populations and the immune response by comparing a bolus infection of third-stage larvae in na?ve sheep with a group previously primed by a trickle infection. The second experiment used staggered doses of ivermectin-resistant larvae to compare the development of adult worms during different durations of trickle infection with ivermectin-sensitive larvae. Infections successfully generated pathological signs of haemonchosis such as anaemia. Image analysis software was used to measure the area and perimeter of worms collected at post-mortem, and the number of eggs present in individual adult females (fecundity) was significantly correlated with worm size. A significant inverse correlation was found between blood lymphocyte counts and worm fecundity. The absence of correlation between worm fecundity and other leukocyte and erythrocyte counts highlighted the specificity of the lymphocyte response. This is the first report of a link between haematology profiles and worm fecundity in haemonchosis. The correlation observed between adult worm size and egg content leads to the hypothesis that egg production in H. contortus is limited by immune regulation of worm size and presumably growth. Mean worm size and fecundity declined as sheep received more prolonged trickle infections before necropsy, confirming previous reports that immune responses to adult worms are enhanced by ongoing larval challenge. Immunohistochemical results showed trends consistent with a Th2 (humoral) immune response which has been implicated in reducing nematode burdens in several species.  相似文献   

19.
A study was conducted of the monthly fluctuations of worm burdens and arrested development of gastrointestinal (GI) nematodes in sheep from a commercial farm of the Ebro valley (Spain). Twenty-four previously helminth-free female lambs (permanent lambs) grazed together with a flock of 500 resident ewes for 12 months following a three lambing/2-year reproductive management system. Two helminth-free lambs (tracer lambs) were added to the flock each month and allowed to graze for 4 weeks. Measurements were made of the population of infective larvae on the pasture, and of levels of serum pepsinogen and faecal worm eggs in ewes and lambs. Additionally, post-mortem worm counts from two tracer and two permanent lambs were used to establish the level of infection at monthly intervals. Three generations of parasites were identified in the experiment. The generation derived from eggs deposited the previous autumn gave rise to the first infection of the animals in January and May. This infection had low consequences for the animals, but it signified the initiation of infection and the resumption of the annual cycle of pasture contamination. The second generation, appearing between June and July, was the year's most important source of infection and gave rise to an outbreak of parasitism in permanent lambs. This was indicated by an increase in levels of serum pepsinogen, the appearance of diarrhoea, and an important decrease in lamb growth rates. The third wave of infection, occurring in October and November, there was less impact than the previous one with respect to the level of infection, but it was the origin of the future over-wintering population. Teladorsagia circumcincta was the predominant species, followed by Haemonchus contortus and Trichostrongylus colubriformis. The highest numbers of worm recovered from both the tracer and permanent lambs were observed in July, with average numbers of 7900 and 19,200, respectively.The inhibition phenomenon was more evident in permanent than in tracer lambs, and mainly affected H. contortus as evidenced by populations exhibiting arrested larvae values of over 70% in January and February.Results obtained in this study confirm the epidemiological importance of the over-wintering L(3) generation as the initial source of the animal's infection and the origin of the annual resumption of pasture contamination cycles.  相似文献   

20.
Nematode populations is stabled ewes of the Rimouski region were studied by means of fecal worm egg counts, fecal culture of larvae, and worm counts at necropsy. It was found that during the winter strongyle egg counts were low, Trichostrongylus eggs being most numerous, The stronglye egg counts increased following lambing and reached peak in June. Ostertagia spp was the principal contributor to this “spring-rise”, with substantial contribution from Trichostrongylus and Haemonchus contortus. The bulk of adult worm populations in winter, however, was made up of Trichostrongylus, whereas the great majority of the populations of Ostertagia spp, H. contortus and Nematodirus spp were inhibited in development at the fourth larval stage. All the worms recovered at necropsy in spring were adults, coinciding with the “spring-rise”.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号