Development and spatial distribution of the free-living stages of Teladorsagia circumcincta and Trichostrongylus colubriformis on pasture: A pilot study

Abstract

AIMS: To measure the development of Teladorsagia (=Ostertagia) circumcincta and Trichostrongylus colubriformis eggs to third-stage infective larvae (L3) at different times of the year. Also, to measure the spatial distribution of L3 across herbage, soil and faeces, in order to assess whether spatial issues could be important in larval dynamics on pasture.

METHODS: Field plots were contaminated with sheep faeces containing approximately 20,000 eggs of each of T. circumcincta and T. colubriformis on five separate occasions, viz 01 December 1996 (summer), 18 March 1998 (autumn), 17 June 1998 (winter), 15 October 1998 (spring), and 23 July 1999 (winter). Replicate plots (n=10) were harvested at intervals for up to 12 months after deposition of faeces, and the number and distribution of L3 were measured. Larvae were sampled from faeces (where these remained), herbage, and three soil zones to a depth of 145 mm.

RESULTS: There were large differences between contamination dates in the percentage of eggs that developed to L3. For both species the highest percentage development was for eggs deposited in December (7.8% and 25.9% for T. circumcincta and T. colubriformis, respectively) and the lowest for June (0.4% and 0.03% T. circumcincta and T. colubriformis, respectively). Development in winter was often delayed, and this was always associated with a low yield of larvae, probably due to compounding mortalities associated with long periods of exposure to low temperatures.

The relative distribution of L3 present on herbage, in faeces or in the soil varied between sampling times. However, overall the most L3 were recovered from soil (74% and 66% for T.circumcincta and T. colubriformis, respectively, averaged over all samples), and the lowest recoveries were from the herbage.

CONCLUSIONS: Although the data are limited, the results indicated that the highest percentage of eggs developed to infective larvae in summer and only minimal development occurred in winter. The data do not support the view that substantial contamination of pastures with sheep parasites occurs over winter. Large numbers of larvae were recovered from soil, which indicates that, assuming they can subsequently migrate onto herbage, soil is a potentially important reservoir ofinfective larvae in New Zealand. Therefore, the spatial distribution of L3 on pasture may affect both the dynamics and transmission of parasite populations. Further work on both these issues is warranted.     

Dynamics of the free-living stages of sheep intestinal parasites on pasture in the North Island of New Zealand. 1. Patterns of seasonal development

Abstract

AIM: To describe the seasonal pattern of development of third-stage infective larvae (L3) from eggs of Teladorsagia (=Ostertagia) circumcincta, Trichostrongylus colubriformis and Haemonchus contortus on pasture in the North Island of New Zealand.

METHODS: Sheep faeces containing known numbers of eggs of all three nematode species were deposited on, or buried in, pasture plots at three sites, viz coastal Manawatu, Upper Hutt Valley, and East Cape hill country. Development was measured by recovering L3 from faeces, herbage and soil 28–31 days after deposition on 13–18 occasions, between January 2005 and July 2006. Analysis of the number of larvae recovered used a mixed model including number of eggs deposited, weight of faeces recovered (an assumed indicator of earthworm activity), site, contamination date, and position of deposited faeces, i.e. on the surface or buried.

RESULTS: There was a significant effect of contamination date on development of all three species, with maximum numbers ofL3 developing between late spring (November) and early autumn (March), and minimum numbers in June and July. There were large differences between species, with H. contortus exhibiting a long period (April to October) where development was close to zero, whereas T. circumcincta developed to some extent all year round. Development of T. colubriformis was intermediate between the other two species.

Burying faeces containing nematode eggs increased the number of L3 recovered compared with surface deposition (p≤0.001), although there were a small number of exceptions involving only T. colubriformis. The weight of faeces recovered at harvest, which was assumed to be an indication of earthworm activity, was correlated with the number of L3 recovered for all species (p<0.001). In a separate analysis, earthworms were assumed tohave been active if <5 g faeces remained at harvest. Where this occurred, the number of L3 of T. colubriformis and T.circumcincta recovered was reduced by 56% and 58%, respectively (p<0.001).

CONCLUSIONS: A marked seasonal pattern of development was observed for all three species, with the most larvae developing in spring-early autumn and the least in winter. This seasonal pattern was most pronounced in H. contortus and least obvious in T. circumcincta. Burying faeces containing eggs generally resulted in more L3 being recovered, whilst the apparent activity of earthworms resulted in fewer larvae being recovered.     

Dynamics of the free-living stages of sheep intestinal parasites on pasture in the North Island of New Zealand. 2. Weather variables associated with development

Abstract

AIM: To identify weather variables associated with the development of eggs of Teladorsagia (=Ostertagia) circumcincta, Trichostrongylus colubriformis and Haemonchus contortus to third-stage infective larvae (L3) under a range of climatic conditions on pasture in the North Island of New Zealand.

METHODS: Sheep faeces containing known numbers of eggs of all three nematode species were deposited on, or buried in, pasture plots at three sites, viz coastal Manawatu, Upper Hutt Valley, and East Cape hill country. Development was measured by recovering L3 from faeces, herbage and soil 28–31 days after deposition, on 13–18 occasions between January 2005 until July 2006. Weather data were recorded at each site, and the association between weather variables and number of L3 recovered was analysed using subsets regression to select best-fitting models from several candidate variables, after adjustment for efficiency of recovery of L3. A multiple linear regression model was then developed for each species, to select weather variables that had both significant and substantive effects on the number of L3 recovered.

RESULTS: For all species, mean daily temperature was the bestpredictor of the number of L3 recovered (p=0.001). For T.circumcincta the final model included mean daily temperature and soil temperature (R²=51%), and for T. colubriformis the model only included mean daily temperature (R²=55%). For development of H. contortus, mean daily temperature was the most significant variable, but moisture in the form of rainfall entropy, i.e. the temporal distribution of rainfall, overthe first 14 days was also significant in the final model (R²=34%).

CONCLUSIONS: Temperature was the most important determinant of developmental success of free-living nematodes on pasture at the study sites, and probably also for other parts ofNew Zealand with similar climates. Moisture was not significant in the development of T. circumcincta or T.colubriformis, implying that under the generally moist temperate climate in New Zealand, moisture is seldom limiting for development of these species. Haemonchus contortusappeared to be sensitive to moisture availability and precipitation in the first 14 days after deposition of faeces. The results of this study will be further developed as part of species-specific climate-driven models of parasite development in New Zealand.     

Survival of infective Ostertagia ostertagi larvae on pasture plots under different simulated grazing conditions

This study was carried out to examine the survival of infective Ostertagia ostertagi larvae (L(3)) on pasture under different simulated conditions of grazing, i.e. mixed grazing of cattle and nose-ringed sows, or grazing by cattle alone. Standardised pats of cattle faeces containing O. ostertagi eggs were deposited on three types of herbage plots, which were divided into zone 1: faecal pat; zone 2: a circle extending 25cm from the edge of the faecal pat; zone 3: a circle extending 25cm from the edge of zone 2. For "tall herbage" (TH) plots, the herbage in zone 2 was allowed to grow naturally, while the herbage in zone 3 was cut down to 5-7cm fortnightly, imitating a cattle-only pasture. For "short herbage" (SH) plots, the herbage in both zones 2 and 3 were cut down to 5-7cm fortnightly, imitating mixed grazing of cattle and sows. The grass in the "short herbage and scattered faeces" (SH/SF) plots were cut as for SH plots, and the faeces were broken down 3 weeks after deposition and scattered within zone 2, imitating the rooting behaviour of co-grazing sows. Five faecal pats from each plot group were collected on monthly basis, along with the herbage from zones 2 and 3 cut down to the ground. Infective larvae were then recovered from both faeces and herbage. The numbers of L(3) recovered from zone 1 were higher in the TH plots than in the other two groups and, furthermore, the larval counts from SH plots were always higher than from SH/SF plots. The three groups followed a similar pattern during the season regarding numbers of L(3) in zone 2, and no clear patterns between plot types were obtained. The presence of L(3) in zone 3 was almost negligible. Important differences were seen throughout the study from the biological point of view; more L(3) were able to survive in faeces on the TH plots, presumably reflecting a better protection from heat and desiccation compared to those in the other plots. The overall results support the idea that mixed grazing of cattle and pigs favour the reduction of O. ostertagi larval levels in pasture. This reduction is mainly due to the grazing behaviour of pigs, which by grazing up to the very edge of the cattle faeces, will either expose the larvae in faeces to adverse environmental summer conditions or ingest cattle parasite larvae, or both.     

Selective and on-demand drenching of lambs: Impact on parasite populations and performance of lambs

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.     

Winter survival in Sweden of L(3)-stage larvae of the ostrich wireworm Libyostrongylus douglassii

Libyostrongylus douglassii, a pathogenic trichostrongylid nematode of the ostrich, was recently identified as a potentially important parasite in ostriches on Swedish farms. This parasite is well adapted to the hot and dry climates of sub-Saharan Africa, the natural habitat of the ostrich. The influence of low temperatures in colder climates, such as in Sweden, on free-living stages of L. douglassii is however insufficiently known. In this study, parasite free ostrich faeces were mixed with infective L(3)-stage larvae of L. douglassii, which had been cultured from eggs obtained from two Swedish farms. Samples of the mixture were placed on a grass surface, and analyses for L(3)-stage larvae were performed at regular intervals. The results of the study showed that L(3)-stage larvae may remain alive during a period of at least 97 days on pasture during the winter season in Sweden, even when the temperature within the samples was repeatedly below -0.1 degrees C, and the air temperature varied between -19.6 and +14.9 degrees C. It was concluded that L(3)-stage larvae of L. douglassii probably have the ability to remain viable on pastures during winter in Sweden.     

Epidemiology of bovine dictyocaulosis in Denmark

A field experiment was conducted over two grazing seaons with calves on a permanent pasture in order to follow the pattern of infection with Dictyocaulus viviparus. Infective larvae persisted during the first, but not during the second, winter of observation. By means of the agar-bile herbage technique, a moderate first peak of infection was demonstrated in the pasture 2–3 weeks before the appearance of respiratory signs in the calves. Fluctuations in faecal larval output were reflected in the herbage contamination with infective larvae close to faecal pats. This, as well as the horizontal dispersion of larvae in the pasture, took place in less than a week. The proportion of lungworm larvae recovered away from faeces was low during a period of dry and hot weather while herbage sampling at two-hour intervals during two days showed an increase in herbage contamination with lungworm larvae, but not with trichostrongyle larvae between 10 a.m. and 12 noon.The infectivity of the pasture was monitored by tracer calves and compared with the results of the pasture sampling. The general course of the infection in the calves and in the pasture was the results of interaction between them. In addition, the pasture infection was influenced by climate and the infection in the calves by the development of immunity. The course of infection in individuals appeared to have an influence on the general course of the infection through the contamination of the pasture.     

Strategic use of anthelmintics to prevent parasitic gastroenteritis in cow-calf herds in California

On the basis of the hypothesis that the peak numbers of infective nematode third-stage larvae (L3) on herbage in winter months results from fall contamination of pastures, 2 methods to reduce fall contamination were tested. In trial 1, morantal sustained-release boluses were administered to 15 fall-calving cows on Sept 7, 1982. Fifteen untreated cows (controls) were placed on separate pastures. Numbers of L3 on herbage during the winter and spring were assessed by use of worm-free tracer calves. In trial 2, 19 cattle due to calve in the fall were administered 200 micrograms of invermectin/kg of body weight, SC, on Sept 2, 1983. Also, 17 cattle similarly were given a placebo injection and served as control animals. Treated cattle were placed on the pasture used by control cattle in trial 1 and control cattle on the pasture used by treated cattle in trial 1. Worm-free tracer calves were again used to assess numbers of L3 on herbage. In trial 1, tracer calves grazing the control animal pasture from January 14 to 28 acquired 37 times as many nematodes as did those grazing the treated animal pasture. In trial 2, the greatest difference observed was a 10-fold increase of nematodes in calves grazing control animal pastures, compared with worm numbers in tracer calves grazing the treated animal pasture.     

Field studies of the immunisation of lambs with drug-abbreviated infections of Trichostrongylus colubriformis and Ostertagia circumcincta

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 circutncincta. 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 signscantly lower dag weight than controls.     

Development and survival of free-living stages of gastrointestinal nematodes of sheep and goats on pasture in the Nigerian derived savanna

Four grass plots were sequentially contaminated with goat faeces containing known numbers of unembryonated eggs of predominantly Haemonchus contortus and Trichostrongylus spp. between October 1982 and April 1983. Four other plots were similarly contaminated with sheep faeces between February and May 1987. An additional plot was repeatedly contaminated with sheep faeces from February to April 1987. Populations of free-living stages in faeces and of infective larvae (L₃) in the herbage were subsequently monitored until the end of April and June of 1983 and 1987 respectively. During February and May 1987 two control cultures of sheep faeces were incubated in the laboratory at 25°C–30°C and at a constant temperature of 50°C and the free-living development was also monitored. L₃ developed very readily in the faeces cultured at 25°C–30°C and in those spread on a grass plot in October, at the end of the wet season, but developed less on the plot contaminated in May at the start of the wet season. Worm eggs in faeces deposited on plots during the hot dry season (December to April) or incubated at 50°C died and disintegrated after 24–48 h exposure to the high environmental temperatures. The results indicate that it is unlikely that gastrointestinal nematodes of sheep and goats can develop or survive on open pasture during the dry season in the Nigerian derived savanna zone.     

Drench-and-shift is a high-risk practice in the absence of refugia

Abstract

AIM: To examine the effect of an anthelmintic treatment to lambs, followed immediately by a shift onto pastures with differing levels of larval contamination, on the development of anthelmintic resistance, in order to support recommendations to farmers regarding drench-and-shift practices for sustainable worm control.

METHODS: Newly weaned Romney lambs (n=72) were dosed with third-stage infective larvae (L3) of two nematode parasite species, Teladorsagia (=Ostertagia) circumcincta and Trichostrongylus colubriformis, comprising benzimidazole-resistant and -susceptible isolates, calculated to yield, after treatment with albendazole, a 95% reduction in faecal nematode egg count (FEC). Once infections became patent (Day 0), lambs were randomised into nine groups of eight animals, treated with albendazole at the manufacturer's recommended dose rate, and moved to individual pastures each previously prepared to have one of three different levels of parasite larval infestation (Treatment 1 = low contamination, Treatment 2 = medium contamination, and Treatment 3 = high contamination), and grazed on those pastures before receiving a second treatment with albendazole at Day 47. Anthelmintic resistance status in each group of lambs was measured using FEC reduction (FECR) and egghatch assays (EHA) after the first anthelmintic treatment, and FECR after the second treatment.

RESULTS: Egg-hatch assays demonstrated significant differences between treatments. The concentration of anthelmintic required to kill 50% of the eggs (LC₅₀) for Treatment 1, comprising the least contaminated pastures, was significantly higher than for Treatments 2 and 3 on Days 33 and 40. Treatment 1 also had a significantly lower FECR at the final anthelmintic treatment, and significantly lower FEC than the other two treatments from Days 26 to 47.

CONCLUSIONS: The results demonstrated that the populations of T. circumcincta and T. colubriformis in lambs treated with anthelmintic had significantly higher levels of albendazole resistance at the end of the grazing period in lambs moved onto pastures with relatively low levels of parasite contamination than those moved onto pastures with relatively higher contamination, confirming drench-and-shift onto ‘clean’ pasture as a high-risk practice for the selection for anthelmintic resistance. While this does not necessarily preclude the use of this practice it does emphasise the importance of taking appropriate remedial action to minimise the risk.     

The evaluation of endophyte toxin residues in sheep fat

Abstract

AIM: To monitor changes in concentrations of lolitrem B and epoxy-janthitrems in the fat of sheep grazing perennial ryegrass infected with wild-type- and AR37-endophyte, respectively, during the time of year when ryegrass staggers would be expected to be observed.

METHODS: Ten 5-month-old lambs with no previous exposure to endophytes were grazed on either wild-type (containing lolitrem B, n = 5) or AR37 (containing epoxy-janthitrems, n = 5) endophyte-infected perennial ryegrass (Lolium perenne L.) pastures between October 2008 and June 2009. Animals were regularly assessed for ryegrass staggers using the Keogh scale (0 = no signs, 5 = severe tremors). When a score of > 3.5 was observed animals were removed from the treatment pastures for 1 month. Fat biopsy samples were taken from each animal at approximately monthly intervals and analysed for endophyte metabolites using high performance liquid chromatography (HPLC) methods developed during this study. Regular herbage samples were also taken and concentrations of endophyte metabolites measured.

RESULTS: Efficient and reproducible methods to analyse both lolitrem B and epoxy-janthitrems in fat were developed. Concentrations of lolitrem B and epoxy-janthitrems in herbage and in sheep fat increased from late November to peak in mid-February. Ryegrass staggers was observed in both groups of sheep at this time. Following 1 month of grazing non-infected pasture mean concentrations in fat of lolitrem B decreased by 43% from 61.8 to 35.3 ppb, and of epoxy-janthitrems by 38% from 1032.0 to 639.5 ppb. Maximum concentrations in herbage of epoxy-janthitrems (35.7 ppm) were higher than of lolitrem B (3.4 ppm), but signs of staggers were less severe in sheep grazing pasture containing the former compared with the latter (median Keogh scores in late February were 2 and 3, respectively), consistent with epoxy-janthitrems being low potency toxins.

CONCLUSION: This study demonstrated that concentrations of epoxy-janthitrems and lolitrem B in sheep fat increased quickly during the initial phase of the study when concentrations in pasture increased, and decreased when animals were removed from pastures containing these compounds. These data will be used in the risk assessment of the endophyte metabolites.     

Effects of grazing undrenched weaner deer on chicory or perennial ryegrass/white clover pasture on the viability of gastrointestinal nematodes and lungworms

This study determined the in vitro effects on the viability of internal parasites of grazing undrenched weaner deer on either chicory (Cichorium intybus) or perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) pasture. One experiment investigated the hatching and development of gastrointestinal nematode eggs and larvae, and the development and motility of L1 lungworm (Dictyocaulus eckerti) larvae, and a second experiment used larval migration inhibition assays to test the viability of L1 lungworm larvae extracted from the faeces of weaner deer grazed on either chicory or pasture when they were incubated with rumen and abomasal fluids from fistulated deer also grazing on chicory or pasture. The incubations were undertaken with and without added condensed tannins purified from chicory and with or without polyethylene glycol (PEG) to bind the tannins. Chicory had no effect on the hatching and development of gastrointestinal nematode eggs and larvae. Grazing chicory reduced the number of lungworm larvae developing to the L3 stage, and L1 lungworm larvae from the faeces of chicory-grazed deer were less viable in rumen and abomasal fluid than larvae from pasture-grazed animals. Abomasal fluid was significantly (P < 0.001) less inhibitory to the migration of L1 lungworms than rumen fluid. When the larvae were incubated in rumen and abomasal fluids from chicory-grazed deer, their passage through sieves was significantly (P < 0.001) reduced in comparison with when they were incubated in the fluids from pasture-grazed deer Adding condensed tannins to rumen fluid increased the inhibition of the migration of L1 lungworm larvae but PEG removed this inhibition; this effect was not observed with abomasal fluid.     

Trichostrongyle infestation in autumn on pastures grazed exclusively by cows or by calves

Larval counts were made on herbage samples collected from 14 calf pastures and 14 cow pastures at each of three different localities in Lower Saxony, Western Germany, in September 1974. Significantly higher numbers of larvae of the genera Ostertagia, Cooperia and Nematodirus were demonstrated on calf pastures than on cow pastures in all three areas. The results suggest that, in the absence of available “clean” pasture, improved control of trichostrongyle infection during late summer and autumn might be achieved by the transfer of calves to cow pastures at that time.     

The effect of diet fed to lambs on subsequent development of Trichostrongylus colubriformis larvae in vitro and on pasture

Contrasting herbage diets were fed to lambs to evaluate their effect on subsequent development of Trichostrongylus colubriformis larvae in faeces and on pasture. The diets had either no condensed tannin (CT), lucerne (Medicago sativa cv. Otaio), white clover (Trifolium repens cv. Tahora), or had moderate to high concentrations of CT, sulla (Hedysarum coronarium cv. Grassland Aokau), Lotus corniculatus (cv. Grasslands Goldie), L. pedunculatus (cv. Grassland Maku), Dorycnium pentophyllum, and Dorycnium rectum. Trials were carried out in summer (warm) and in autumn (cool and moist). In summer, egg viability was evaluated in vitro with egg hatch and larval development assays. In both seasons faeces were placed on pasture to compare recovery of eggs and larvae from faeces and larvae from herbage on the high and low fertility farmlets on the AgResearch Ballantrae Hill Country Research Station. D. rectum and D. pentophyllum diets decreased (P<0.01) egg hatching and larval development in laboratory assays relative to other diets. In summer, the number of larvae recovered from faeces placed on pasture was far greater (P<0.001) if the lambs had been fed lucerne than any other diet, whereas recovery was always lowest from faeces of sheep fed D. rectum and D. pentophyllum. Although dietary differences were lower in autumn than in summer, larval recoveries were lower (P<0.05) from faeces of lambs fed D. rectum and L. corniculatus than from white clover, lucerne and sulla diets. This study indicates that the diet of the host can have a significant impact on egg hatching and the subsequent development of T. colubriformis larvae in the laboratory and in the field. In particular, D. rectum consistently reduced T. colubriformis development. Effects measured in vitro generally under-estimated effects measured under field conditions.     

The effect of elemental Zn boluses on concentrations of Zn in serum and faeces of South American camelids

ABSTRACT

Aims: To monitor the effect of using long-acting Zn boluses on the Zn status of a group of South American camelids, using measurements of concentrations of Zn in faeces and serum.

Methods: As part of a facial eczema (FE) prevention programme, 15 camelids were treated with long-acting Zn boluses designed for preventing FE in sheep. Based on bodyweight, 13 alpacas (Vicugna pacos) received two boluses (26.4?g Zn/bolus) and two llamas (Lama glama) received three boluses. In order to monitor Zn status, measurements were made of concentrations of Zn in serum and faeces immediately prior to bolus treatment (Week 0) and 4, 6, 8 and 10 weeks later. Gamma glutamyl transferase (GGT) activity in serum was measured at Weeks 0 and 8.

Results: Two alpacas regurgitated the boluses; in one case the animal was quickly re-treated but this was not possible in the second animal. Mean concentrations of Zn in faeces were higher at all time points compared to Week 0 (p?<?0.001). Peak concentrations were measured at Week 8, and concentrations >120?mg/kg fresh weight (FW), suggested as being protective in calves, were only measured in all (13/13) treated camelids at Week 6. Mean concentrations of Zn in serum differed between weeks of sampling but changes were not consistent, and concentrations did not exceed 18?μmol/L following treatment. There was no evidence of a natural sporidesmin challenge during the study period and activity of GGT in serum of all animals was <45?IU/L.

Conclusions: Treatment with Zn boluses significantly increased concentrations of Zn in faeces but not in serum, but peak concentrations in faeces were only detected 8 weeks after treatment.

Clinical Relevance: The delay in achieving concentrations of Zn in faeces which were associated with protection against FE in calves, combined with the difficulties of administering boluses to camelids, means that we do not believe that Zn boluses should be used as the primary method for preventing FE in camelids. We recommend that FE prevention in camelids should focus on minimising spore production in pasture through the use of fungicides, grazing management and alternative forages, with boluses only used when it is thought that these methods are unlikely to provide sufficient protection against FE. Such use should always be under the guidance of a veterinarian and monitoring of serum GGT activity should be used to ensure that FE control is being achieved.     

Migration of gastrointestinal nematode larvae from cattle faecal pats onto grazable herbage

This study investigated the effect of successive harvests of grazable herbage around cattle faecal pats on the population dynamics of infective gastrointestinal nematode larvae (L(3)). Faecal material, collected from naturally infected calves, was deposited as pats during summer, autumn and winter on three different topographical aspects within a moist, temperate region of New Zealand. Herbage was harvested four times (22-248 days) from around the faecal pats to a height of 2cm in three radial zones (0-20cm, 20-35cm and 35-45cm from the centre of the faecal pat) and L(3) extracted. Harvest date was determined by herbage mass to simulate grazing events. L(3) extracted from herbage were predominantly Cooperia spp. More L(3) were recovered from faeces deposited in summer and autumn, than those deposited during winter. L(3) concentration on herbage was highest (P<0.001) in the zone nearest the pat for all except the fourth harvest. Mean concentrations of L(3) on herbage were 11,447, 3154, 337 and 102 L(3)/kg dry matter herbage, for the four successive harvests, respectively. Microclimate differences as affected by aspect had a marked effect on herbage growth, but did not significantly affect L(3) concentration on herbage. In this study, L(3) remained aggregated close to the faecal pats they emerged from even after two successive harvests and significant rainfall. Successive harvests simulated the effect of repeated grazing events by a non-infective stock class. Two such grazings and the associated time, reduced L(3) presence on grazable herbage to <3% of the original population. Grazing strategies to generate clean pasture for vulnerable cattle are discussed in relation to these results.     

Relative contributions of late dry-season and early rains pasture contaminations with trichostrongyle eggs to the wet-season herbage infestation in eastern Nigeria

Two worm-free grass paddocks, P1 and P2, were artificially contaminated in March and April-May, respectively, with bovine faeces containing known numbers of trichostrongyle (mainly Cooperia, Haemonchus and Trichostrongylus spp.) eggs in order to determine the relative contributions of late dry-season and early rains pasture contaminations to the wet-season herbage larval infestation in Nsukka, eastern Nigeria. The resulting herbage infestation was assessed by means of larval counts and tracer studies. A sudden rise in herbage infestation occurred simultaneously in both paddocks in late April, this apparently being determined by the onset of the first substantial rainfall of the wet season. Peak infestations in both paddocks also occurred simultaneously in May. The infestation in P1 was much larger, and the larval population persisted longer, than that in P2 and later gave rise to a second smaller peak in June. No L3 were recovered in herbage samples from either of the paddocks after the third week of July. Both paddocks were infective to goats in May-June, while P2 was also infective in July-August. The results suggest that in the Nigerian derived savanna the initial wet-season herbage infestation in pastures grazed by infected cattle during the dry and wet seasons will consist of L3 from late dry-season and early rains pasture contaminations, the former being the major contributor to the infestation. Consequently, pastures contaminated during the late dry season may not be safe for susceptible animals to graze at the start of the succeeding rainy season.     

THE EPIDEMIOLOGY OF EQUINE STRONGYLOSIS IN SOUTHERN QUEENSLAND 1. The Bionomics of the Free-Living Stages in Faeces and on Pasture

SUMMARY Development of the free-living stages of strongylid nematodes of the horse to the infective stage occurred in faeces in all months of the year in southern Queensland, at a rate which depended on the season. Most rapid development to the infective stage occurred in the warmer months, with the hatching of strongyle eggs being completed in 2 days in summer. During the winter, egg hatching continued for over 2 weeks. Larval moults proceeded at a faster rate in summer—all larvae were infective in 7 days during the hottest months, but it was as long as 5 weeks before all were infective in winter. However, even though development was rapid in summer, survival rates varied from 1 to 10%, in contrast to the spring and autumn, when over 80% reached the infective stage. One percent of larvae in faeces survived for up to 20 weeks in autumn and winter, but for only 4 weeks in summer. These results highlight the inadequacy of short-term pasture spelling for all but the hottest months. Infective larvae were found on herbage in all months of the year, but greatest numbers were recovered in spring and early summer, and in autumn and early winter. The relationship of pasture infestation to migration of larvae from Paecal reservoirs in response to rain was clearly shown. Most infective larvae were found within 30 cm of faecal masses, and in fact 89% of all larvae isolated from herbage in this study were found within 15 cm of faeces. Migration of larvae from faeces to herbage occurred with falls of rain as small as 25 mm. Horse faecal masses dried out completely in 6–8 days in summer and in 14–16 days in winter. Strongyle larvae developed to the infective stage in faeces in the absence of rain, although many remained in the pre-infective stage and completed their development when rain fell. This study shows that massive contamination of pastures with the eggs of strongylid nematodes must be prevented in spring and autumn if susceptible young horses are not to be at serious risk.     

The Effect of Anthelmintic Capsules on the Egg Output and Larval Viability of Drug-resistant Parasites

Challenge with an equal mix of drug-resistant and drug-susceptible larvae of Teladorsagia circumcincta resulted in infections in groups of lambs (n = 6) either untreated or given controlled-release capsules, containing either albendazole or ivermectin. Lambs treated with albendazole capsules contained similar numbers of adult worms at necropsy to the other groups but had no detectable faecal egg count. Animals treated with ivermectin capsules had similar worm burdens and faecal egg counts to the control group but the worms had significantly higher numbers of eggs in utero. These results provide evidence for suppression of egg production by both anthelmintic treatments. The observation that albendazole caused a significant reduction in the developmental success of parasite eggs also has implications for the use of faecal egg count as an indicator for pasture contamination with resistant parasites. In two further groups of lambs, either untreated or given albendazole capsules, treatment caused a significant reduction in egg count and adult worm burden of Trichostrongylus colubriformis. No significant effects were observed on in utero egg counts or egg viability and the apparent effect on the number of eggs produced in faeces per adult female was not significant (p = 0.077). There was, therefore, no evidence that albendazole controlled-release capsules caused suppression of egg output in this species.