Control of nematode parasites by grazing management—I. Decontamination of cattle pastures by grazing with sheep

Between December and June, six paddocks that had been contaminated naturally with infective larvae of nematode parasites of cattle, were each subjected to one of six grazing treatments. The effects of these treatments on the infectivity of the pastures were assessed by slaughter and total worm counts of calves which subsequently grazed the paddocks, and by counts of larvae on pasture samples. Grazing by sheep during autumn resulted in reduced populations of Ostertagia ostertagi and Trichostrongylus axei, both in calves and on the pasture for up to 12 months after treatment. Similar effects were noted on pasture grazed by cattle repeatedly dosed with anthelmintics, and on ungrazed pasture. There was little effect of any treatment on numbers of Cooperia oncophora. It was concluded that the level of autumn contamination was of importance in determining the numbers of O. ostertagi in the following spring and summer.     

The survival of the free living stages ofOstertagia circumcincta during drought

The hot dry summer experienced in England in 1976 did not result in the complete destruction of the free living stages ofOstertagia circumcincta derived from eggs deposited on the herbage in the spring. The surviving larvae are of significance in perpetuating infection in grazing animals and on the pastures for future years.     

Faecal egg output and herbage contamination with infective larvae of species of Ostertagia and Oesophagostomum from naturally infected farmed sika deer Cervus nippon in Lithuania

Faecal egg outputs and subsequent herbage larval contamination with third stage larvae (L3) of Ostertagia spp. and Oesophagostomum spp. from a herd of naturally infected sika deer Cervus nippon were examined in the same pasture in 2001/2002 in Lithuania. Sika deer were infected with Ostertagia circumcincta, O. kolchida, O. spiculoptera, Oesophagostomum radiatum, O. columbianum and O. venulosum. Faecal egg output in adult deer peaked in the spring during the periparturient period and also in late August, compared with a peak in egg output in calves during September to November. Herbage contamination with L3 of Ostertagia spp. peaked in June but larvae were not present on pastures from the end of September. Hence the highest risk of infection was in early born calves grazed on pastures in July. Infective larvae of Oesophagostomum spp. did not survive during the winter, but the nematodes were reintroduced onto the pastures by adult deer in the spring.     

Epidemiological Investigations of Trichostrongylid Infections in Young Cattle in Different Parts of Norway

The occurrence of trichostrongylid nematodes in young cattle was studied in relation to climate and geographical location, by examination of herbage and faecal samples from 8 farms in 7 different regions in Norway, during 3 consecutive summers. Species of Ostertagia and Cooperia were dominant. Infective larvae, especially those of Ostertagia, were able to survive the winter in the pasture to a great extent in all the areas studied. The spring larval counts varied considerably from place to place, and from year to year, but were often at fairly high levels. This confirms previous findings that the larvae which overwinter on the pasture may be a major cause of losses. Overt clinical disease, however, was only seen at 1 farm during this investigation. The large number of larvae often seen in the autumn seems to be of less significance as a cause of disease, due to the late appearance, but is of major importance as a source of the larvae which survive the winter in the pasture and infect young cattle the following spring. There was no obvious correlation between pasture larval counts and the climate, except that there seemed to be higher counts in the warmer parts of the country, where the grazing season is also longer. The only place were both faecal egg counts and larval counts in the herbage were consistently low, was in the very far north.     

Host-induced effects on the morphology of Ostertagia circumcincta in grazing sheep

Waller P. J. and Thomas R. J. 1978. Host-induced effects on the morphology of Ostertagia circumcincta in grazing sheep. International Journal for Parasitology8: 365–370. Morphological changes are described in adult Ostertagia circumcincta recovered from lambs slaughtered monthly from June to November. Comparisons were made between continuously grazed principal lambs exposed to infection for increasingly long periods, and tracer Iambs exposed for only four weeks. Lambs were either slaughtered immediately off pasture or held 2 weeks under worm free conditions before slaughter. Although no resistance to establishment of infection occurred, shown by comparable worm burdens of principals and tracers, a rapid parasite population turnover was observed in the principal lambs which ceased once the lambs were removed from the infected pasture. Significantly fewer adult female Ostertagia with fully developed vulval flaps were recorded in principals compared to tracers. Such differences are considered to be primarily host induced responses which rapidly come into play, evidenced by the entire populations of developing female worms in tracers slaughtered immediately off pasture showing arrested vulval flap development after they had completed development in those tracers held for a further two weeks. A progressive reduction in the proportion of adult male worms also occurred in the principal lambs. Population density was shown to have an inverse correlation with worm size. By analogy, it is suggested that seasonal change in the presence of cuticular inflations in Haemonchus contortus females with linguiform vulval flaps may be primarily host induced, rather than a change in the relative fitness of discrete genotypes.     

Gastro-intestinal nematode infection in lambs — A model based on climatic indices for forecasting peak pasture larval contamination

The parasiteOstertagia circumcincta is the primary cause of parasitic gastro-enteritis in lambs during their first season at grass. The life-cycle of this nematode parasite involves the development and survival of the free-living stages on pasture. Accordingly the pasture is the site of deposition, development and transmission of infection and meteorological factors affecting the pasture will affect the parasites. In this paper two empirical models for forecasting the timing of the summer wave of infective larvae on pasture are presented. These models are similar in form to that described by Starr and Thomas (1980) but involve different approaches to assessing the temperature and moisture components of the daily index value. Further, using the prediction model described by Paton, Thomas and Waller (1984) as an investigative tool, certain tentative suggestions are made as to a general fundamental weakness of empirical index methods.     

Observations on the dynamics of worm burdens in lambs infected daily with Ostertagia circumcincta

Hong C., Michel J. F. and Lancaster M. B. 1987. Observations on the dynamics of worm burdens in lambs infected daily with Ostertagia circumcincta.International Journal for Parasitology17: 951–956. Groups of lambs were infected daily with either 250, 500 or 1000 Ostertagia circumcincta larvae and the course of their worm burdens by post mortem examination at five intervals of time was studied. The number of worms appeared to be related to the rate of intake of larvae. A morphometric study of female worm lengths and observations on the incidence of reduced vulval flaps indicated that the population of worms turned over rapidly. The response of a small number of lambs appeared to be abnormal.     

Variation in size of Ostertagia circumcincta,a nematode parasite of sheep,induced experimentally and during preparation and preservation

Summary This investigation was undertaken to determine the effect of formol-saline fixation and subsequent preparation on the length of Ostertagia circumcincta, a gastrointestinal parasite of sheep. Such induced changes in worm lengths were compared with the size distribution in two experimental populations in lambs, one of which was helminthologically susceptible and the other highly resistant. It was concluded that variation in worm length caused by fixation was not significant when compared to the variation encountered naturally in worm populations. ac]19851213     

Distribution of trichostrongylid nematodes in the abomasum of sheep

The distributions of Haemonchus contortus, Ostertagia circumcincta and Trichostrongylus axei during their development in lambs were studied by freezing and sectioning the abomasum and then recovering the worms from the contents and mucosa of each section. In previously worm-free lambs, the distribution of fourth stage H. contortus was very regular, the frequency of larvae being highest in the anterior fundic area and then decreasing in each section towards the pylorus. The distributions of the early larval stages of O. circumcincta and T. axei were variable but tended to be biomodal, with one peak of larvae in the fundic area and a second in the pyloric area. It is suggested that the difference in distribution between H. contortus and the other two species may be due to a difference in the rate of response of exsheathed third stage larvae to stimuli in the abomasum. In the later stages of development, H. contortus and O. circumcincta tended to migrate towards the pyloric area. In previously infected lambs, the distribution of inhibited early-fourth stage H. contortus was similar to that of normally developing fourth stage larvae in previously worm-free lambs and appeared to be unaffected by the host response which caused an altered distribution and rejection of late-fourth stage and adult worms. The rate of rejection of adult O. circumcincta differed between the fundic and pyloric areas of the abomasum, which suggests that the host response in these two areas may be different.     

Tracking gastrointestinal nematode risk on cattle farms through pasture contamination mapping

Gastrointestinal nematode (GIN) parasites in grazing cattle are a major cause of production loss and their control is increasingly difficult due to anthelmintic resistance and climate change. Rotational grazing can support control and decrease reliance on chemical intervention, but is often complex due to the need to track grazing periods and infection levels, and the effect of weather on larval availability. In this paper, a simulation model was developed to predict the availability of infective larvae of the bovine GIN, Ostertagia ostertagi, at the level of individual pastures. The model was applied within a complex rotational grazing system and successfully reproduced observed variation in larval density between fields and over time. Four groups of cattle in their second grazing season (n = 44) were followed throughout the temperate grazing season with regular assessment of GIN faecal egg counts, which were dominated by O. ostertagi, animal weight and recording of field rotations. Each group of cattle was rotationally grazed on six group-specific fields throughout the 2019 grazing season. Maps and calendars were produced to illustrate the change in pasture infectivity (density of L3 on herbage) across the 24 separate grazing fields. Simulations predicted differences in pasture contamination levels in relation to the timing of grazing and the return period. A proportion of L3 was predicted to persist on herbage over winter, declining to similar intensities across fields before the start of the following grazing season, irrespective of contamination levels in the previous year. Model predictions showed good agreement with pasture larval counts. The model also simulated differences in seasonal pasture infectivity under rotational grazing in systems that differed in temperature and rainfall profiles. Further application could support individual farm decisions on evasive grazing and refugia management, and improved regional evaluation of optimal grazing strategies for parasite control. The integration of weather and livestock movement is inherent to the model, and facilitates consideration of climate change adaptation through improved disease control.     

Larval and early post-larval shell of three deep-sea Scaphopoda (Mollusca) from the southwest Atlantic

The larval shells of Antalis circumcincta (Watson, 1879) (order Dentaliida), Pertusiconcha callithrix (Dall, 1889) (order Gadilida) and of an undetermined species of uncertain systematic position are described. The material studied comprises mainly samples from deep waters, collected by expeditions along the southeast coast of Brazil. The larval shell of the three taxa matches other types previously described in the literature. Antalis circumcincta and P. callithrix have four regions (protoconch A, protoconch B, teleoconch A, teleoconch B), but differ in dimensions and sculpture from each other, while the undetermined species has three regions (protoconch A, protoconch B, teleoconch B). A morphometric approach combined with a discriminant analysis also indicates that the three taxa are significantly distinct. This study confirms patterns of larval shells at the taxonomic rank of orders but other supraspecific patterns remain uncertain.     

Observations on parasitic gastroenteritis and bronchitis in grazing calves: effect of low level feed incorporation of morantel in early season.

Pott J. M., Jones R. M. and Cornwell R. I. 1979. Observations on parasitic gastroenteritis and bronchitis in grazing calves: effect of low level feed incorporation of morantel in early season. International Journal for Parasitology9: 153–157. Twenty-four castrated Friesian calves were divided into two equal groups on a body weight basis and grazed separate halves of an infected pasture. One group was given 1.5 mg/kg per day morantel tartrate in the feed over a period extending from 2 weeks before turning out in early May to early July. The other group of calves received an equivalent amount of unmedicated food as controls. Pasture larval counts showed a similar pattern and level of infection from February to July on both pastures. This consisted of a fall from moderate winter levels to very low levels in April/July. The control pasture then showed a typical sharp rise in August to high levels extending through September and falling to moderate levels in October. The pasture being grazed by treated calves showed only a small rise in larval counts in August. The total pasture contamination was reduced by 85% compared with controls during August/October. Faecal egg and larval counts showed similar differences between treated and control calves. Mild clinical signs of parasitic gastroenteritis and bronchitis were seen in controls but not in the treated group. The latter had a weight gain advantage of 20.5 kg the difference becoming marked in the last month of the trial.     

A tandemly repetitive DNA sequence is present at diverse locations in the genome of Ostertagia circumcincta

A novel repetitive DNA sequence in the sheep parasitic nematode Ostertagia circumcincta was cloned and sequenced. This 1.2-kb sequence (Oc1B) was not found in the closely related cattle parasite Ostertagia ostertagi, nor in the more distantly related sheep parasites Haemonchus contortus or Trichostrongylus colubriformis. Sequences similar to Oc1B were found at various genomic locations and contained a pair of 33-bp direct repeats. Oc1B also contained a single copy of a 218-bp sequence (designated OcREP) which was present in 100 to 200 copies in the O. circumcincta genome and mostly organized in distinctive tandem arrays. The dual organizational pattern of OcREP as both a satellite-like sequence as well as interspersed as single copies amongst dissimilar sequences adds to the growing evidence for the fluidity of the parasitic nematode genome, and of eukaryotic genomes in general.     

Effect of host plant on parasitism ofHelicoverpa armigera (Lep.: Noctuidae) byMicroplitis demolitor (Hym.: Braconidae)

Microplitis demolitor Wilkinson is an important larval parasitoid ofHelicoverpa armigera (Hübner) andH. punctigera (Wallengren) in Australia. The effect of host plant on parasitism of second instarH. armigera byM. demolitor was investigated in a glasshouse experiment. Parasitism was low (0%) on chickpea. Moderate to high levels of parasitism (22.4% to 75.4%) were recorded on sorghum, sunflower, maize, cotton and soybean. The results suggest that releases of larval parasitoids into chickpea are unlikely to enhance parasitismlevels during the first spring generation ofHelicoverpa spp.     

Unexpected larval habit of Listronotus bonariensis (Coleoptera: Curculionidae) raises questions about population dynamics analysis and management

Listronotus bonariensis (Kuschel) is a pest of agriculturally important graminaceous species, with mining larvae that kill the stems of the host plants. In this study, larval populations were measured in spring and summer in irrigated dairy grassland comprising Lolium perenne L. (cv. Nui) with and without the endophyte Epichloë festucae var. lolii Latch, M.J. Chr. and Samuels and Poa annua L.. Larvae were extracted from tillers taken from the swards of these two grass species and extracted from turves, and L. bonariensis population densities were estimated from tiller and turf larval counts on a m⁻² basis. Over the study period, the total number of larvae and larval densities extracted from turves was on average 2× greater than indicated from tillers. In most seasons, larval densities from turves were significantly higher than those from the tillers, though there was no correlation between tiller and turf larval densities. Mean head capsule widths of larvae emerging from turf samples showed significant seasonal effects compared with tillers, while mean head capsule widths of all four instars were significantly greater when extracted from tillers compared with turves. There was a significant endophyte effect on head capsule widths of larvae collected in summer, but the effect was not consistent across instars or source. Conversely, no significant endophyte effect on head capsule width was found in spring populations from either tillers or turves. This study shows that in irrigated dairy pasture, a high proportion of L. bonariensis larvae can live externally of tillers, presumably among the organic matter around the base of grasses in irrigated dairy pasture, and that density estimates based only on tiller populations will have significantly underestimated actual numbers. Having a precise indication of larval population densities is essential when developing life tables or determining economic damage threshold levels.     

Larval secretions and food odors affect orientation in femalePlodia interpunctella

Substrates contaminated by wandering fifth instar larvae ofPlodia interpunctella (Hübner) (Lepidoptera: Pyralidae) elicit oviposition by conspecific female moths, and larval rearing diet enhances oviposition and also induces upwind flight. Two-choice oviposition assays determined that four-day-old gravid femaleP. interpunctella preferred to lay eggs on dishes containing cornmeal-based rearing diet compared to empty dishes. Pieces of cheesecloth contaminated by fifth instar larvae elicited more oviposition than untreated cheesecloth or dishes with food. The combination of larval contamination and food was preferred over food only or larval contamination only in both two- and four-choice experiments. The factor(s) in larval contamination responsible for eliciting oviposition in female moths was extracted in hexane, confirming that organic semiochemicals are responsible for the effect. The oviposition-eliciting activity of larval contamination was retained on cheesecloth for up to 30 days following treatment with larvae, suggesting the active component(s) is stable and of low relative volatility. In two-choice windtunnel bioassays female moths initiated flight only when rearing food was present in one of the treatments, and they displayed the highest landing responses to a combination of larval contamination and food. Earlier work onP. interpunctella and related pyralid species found that larval contamination due to secretions from the mandibular glands acted as both a spacing pheromone for wandering larvae and as a kairomone for host-seeking parasitoid wasps. The present study suggests that the same or a similar secretion acts as an oviposition-eliciting pheromone for conspecific females.     

Taxonomic revision of the genus <Emphasis Type="Italic">Orloffia</Emphasis> (Nematoda: Ostertagiinae) based on an ITS-2 rDNA study

A comparative study of ITS-2 rDNA of the nematodes of the genera Orloffia, Ostertagia, Teladorsagia, and Trichostrongylus was performed. The obtained results allow us to consider Orloffia, Ostertagia, and Teladorsagia as closely related but distinct genera. The results of the study indicate that O. bisonis is the only valid species in the genus Orloffia, which has two morphologically distinct forms of males: O. bisonis (major morph) and O. kasakhstanica (minor morph). The percentage of similarity of ITS-2 sequences was 83.3–84.5% between Orloffia spp. and Ostertagia ostertagi, 84.9–86.1% between Orloffia spp. and Teladorsagia circumcincta, and 73.8–74.6% between Orloffia spp. and Trichostrongylus colubriformis.     

Biological control of trichostrongylid infections in calves on pasture in Lithuania using Duddingtonia flagrans, a nematode-trapping fungus

The effect on the pasture contamination level with infective trichostrongylid larvae by feeding the nematode-trapping fungus, Duddingtonia flagrans at two dose levels to first time grazing calves was examined in Lithuania. Thirty heifer-calves, aged 3-6 months, were divided into three comparable groups, A, B and C. Each group was turned out on a 1.07 ha paddock (a, b and c). The paddocks were naturally contaminated with infective trichostrongylid larvae from infected cattle grazing the previous year. Fungal material was fed to the animals daily during a two month period starting 3 weeks after turnout. Groups A and B were given 10(6) and 2.5x10(5) chlamydospores per kg of live weight per day, respectively, while group C served as a non-dosed control group. Every two weeks the heifers were weighed and clinically inspected. On the same dates, faeces, blood and grass samples were collected. From mid-July onwards, the number of infective larvae in grass samples increased markedly (P<0.05)on paddock c, whereas low numbers of infective larvae were observed on paddocks a and b grazed by the fungus treated groups. However, the results indicate that administering fungal spores at a dose of 2.5x10(6)chlamydospores per kg live weight per day did not significantly prevent parasitism in calves, presumably due to insufficient suppression of developing infective larvae in the faeces. In contrast, a dose of 10(6) chlamydospores per kg lowered the parasite larval population on the pasture, reduced pepsinogen levels (P<0.05), and prevented calves from developing parasitosis.     

Biology of gastrointestinal nematodes of ruminants

The development and survival of free-living stages of gastro-intestinal nematodes of small ruminants are influenced by several abiotic and biotic factors. Within the abiotic factors, most important are the environmental temperature and humidity. They regulate the development of larvae from eggs dispersed on the pasture by the animals faeces. Each parasite species that infect ruminants requires a different time to development, depending on temperature and humidity. Among trichostrongylids, Ostertagia, Teladorsagia and Nematodirus show a strong adaptation to low temperatures. Nematodirus larvae are able to survive to winter inside the egg shell. Temperature and humidity influence the distribution and survival of larvae on pasture. The larval third stage can migrate from faeces to pasture vegetation and they accumulate at the basis of vegetation where stay during the day or in the soil to avoid the desiccation. The forage species affects the migration of larvae on herbage too. Many biological factors contribute to disperse the larvae on the pasture. Dung burying beetles, coprophagous beetles and earthworms can greatly reduce the larvae of some trichostrongylids on pasture. They contribute to the spread of the faecal material on the pasture and allow the larval death as a consequence of drying.     

The influence of weather and egg contamination on the development of third-stage larvae of Cooperia oncophora on pasture.

The influence of weather and egg contamination on the dynamics of herbage contamination with infective larave of Cooperia oncophora was investigated on artificially contaminated grass plots and in a grazing experiment with 24 first-year grazing calves from May to October 1987 in Lower Saxony, Germany. On the experimental plots the larval translation was highest at the beginning of July and in the second part of September, following high mean weekly temperatures. Between July and September peak recovery of larvae from herbage occurred 4 weeks after contamination. A seasonal pattern of larval translation similar to that on the experimental plots could be demonstrated on the grazed pastures when the number of larvae per m2 of pasture had been adjusted to the previous egg output by means of a contamination index. The resulting 'relative larval density' is regarded as a good indicator for larval development on pasture. From July to September the larval population on pasture resulted mainly from the egg contamination 2-3 weeks earlier. The short persistence of the infective larvae on herbage was probably due to the frequent and heavy rainfall throughout the season, causing a passive washout of larvae into the soil. On single pastures the larval density started to increase within 1 week after the calves had first contact with these fields. The impact of the calves on the distribution of larvae is discussed.