Comparative analysis of destruction of the infective forms of Trichuris trichiura and Haemonchus contortus by nematophagous fungi Pochonia chlamydosporia; Duddingtonia flagrans and Monacrosporium thaumasium by scanning electron microscopy

The present study aimed to demonstrate by scanning electron microscopy (SEM) the in vitro predatory activity of nematophagous fungi Pochonia chlamydosporia (VC1 and VC4 isolates) Duddingtonia flagrans (AC001 isolate) and Monacrosporium thaumasium (NF34a isolate) on eggs of Trichuris trichiura and infective larvae (L3) of Haemonchus contortus. The work was divided into two experimental tests (A and B). In tests A and B, the predatory activity of nematophagous fungi P. chlamydosporia, D. flagrans and M. thaumasium on eggs of T. trichiura and H. contortus L3 was observed. After 6 h, in test A, isolates P. chlamydosporia (VC1 and VC4) had a role in destroying eggs of T. trichiura. For fungi D. flagrans and M. thaumasium the ovicidal activity on T. trichiura eggs was not observed. Test B showed that D. flagrans (AC001) and M. thaumasium (NF34a) were capable of predating H. contortus L3, but no predation by the fungus P. chlamydosporia was seen. These fungi can offer potential for the biological control of nematodes.     

Assessing the efficacy of Duddingtonia flagrans chlamydospores per gram of faeces to control Haemonchus contortus larvae

The aims were (a) to quantify the number of Duddingtonia flagrans chlamydospores per gram of faeces (CPG) recovered from sheep administered with different oral doses and, (b) to describe the relationship between CPG and eggs per gram of faeces (EPG) on the efficacy to reduce Haemonchus contortus infective larvae. Three doses of chlamydospores per kg BW were orally administered during seven days: (T1) non treated control group, (T2) 1 × 10⁶, (T3) 2.5 × 10⁶ and (T4) 5 × 10⁶. Three lambs, infected with H. contortus, were used per group. Faeces were obtained from the rectum of each lamb during the fungal administration period (days 0–6) and for six days after that period. Four coproculture replicates were made from each animal in days 2, 4, 6, 8 and 10. A higher chlamydospore dose produced higher CPG in faeces (p < 0.05), but a clear dose dependent effect was not found either in the larvae reduction or in the CPG:EPG ratio. When ratios were re-analyzed, independently of the treatment groups of origin, a better efficacy was obtained with a ratio from 5 to 10 CPG:EPG and a higher ratio (>10 per egg) showed a lower reduction efficacy (p < 0.05). The binomial analysis showed that for each unit of increment in CPG:EPG ratio there was a reduction of larvae number until a point (between 5 and 10 CPG:EPG) where no further reduction was detected. The surface response test indicated that the number of larvae was reduced by CPG until possible saturation. The highest CPG:EPG ratios did not necessarily improve efficacy of D. flagrans.     

Biological control of horse cyathostomin (Nematoda: Cyathostominae) using the nematophagous fungus Duddingtonia flagrans in tropical southeastern Brazil

The viability of a fungal formulation using the nematode-trapping fungus Duddingtonia flagrans was assessed for the biological control of horse cyathostomin. Two groups (fungus-treated and control without fungus treatment), consisting of eight crossbred mares (3–18 years of age) were fed on Cynodon sp. pasture naturally infected with equine cyathostome larvae. Each animal of the treated group received oral doses of sodium alginate mycelial pellets (1 g/(10 kg live weight week)), during 6 months. Significant reduction (p < 0.01) in the number of eggs per gram of feces and coprocultures was found for animals of the fungus-treated group compared with the control group. There was difference (p < 0.01) of 78.5% reduction in herbage samples collected up to (0–20 cm) between the fungus-treated group and the control group, during the experimental period (May–October). Difference of 82.5% (p < 0.01) was found between the fungus-treated group and the control group in the sampling distance (20–40 cm) from fecal pats. During the last 3 months of the experimental period (August, September and October), fungus-treated mares had significant weight gain (p < 0.01) compared with the control group, an increment of 38 kg. The treatment with sodium alginate pellets containing the nematode-trapping fungus D. flagrans reduced cyathostomin in tropical southeastern Brazil and could be an effective tool for biological control of this parasitic nematode in horses.     

Predatory capability of the nematophagous fungus Arthrobotrys robusta preserved in silica gel on infecting larvae of Haemonchus contortus

Biological control of gastrointestinal nematodiasis in ruminants is an alternative to reduce the number of infective larvae. The fungal isolates predatory activity preservation is a basic requirement for the success of this control type. The aim of this work is to evaluate the predatory capacity of the fungus Arthrobotrys robusta (isolate I-31), preserved on silica gel on infective larvae of Haemonchus contortus under laboratory conditions on 2 % water agar (2 % WA). In this essay, A. robusta storage on silica gel showed successful predatory activity on H. contortus L₃ larvae (p?<?0.01) compared to the control group. Nematophagous fungi were not observed in the control group during the experiment. There was a significant reduction (p?<?0.01) of 73.84 % in the means of H. contortus (L₃) recovered from treatment with isolate I-31 compared to the control without fungi. Results indicate that A. robusta (I-31) could survive stored on silica gel for at least 7 years and keep its predatory activity on H. contortus (L₃).     

Biological control of cyathostomin (Nematoda: Cyathostominae) with nematophagous fungus Monacrosporium thaumasium in tropical southeastern Brazil

Horses are hosts to a wide variety of helminthes; the most important are the cyathostomin, or small strongyles. The viability of a fungal formulation (pellets) using the nematode-trapping fungus Monacrosporium thaumasium was assessed in biological control of horse cyathostomin. Two groups (fungus-treated and control) consisted of six mares in each group, crossbred (ages of 2.5 and 3.5 years), were placed in pastures of Cynodon sp. naturally infected with horse cyathostomin larvae. In the treated group, each animal received 1g/10 kg body weight (0.2g/10 kg live weight of fungus) of pellets of sodium alginate matrix containing the fungus M. thaumasium orally, twice a week for 6 months. In the control group, animals received (1g/10 kg body weight) of pellets without fungus. The egg count per gram of feces showed difference (p<0.01) in the animals treated with the fungus in relation to the control animals during all months of the experiment. The EPG percentage decrease were 87.5%, 89.7%, 68.3%, 58.7%, 52.5% and 35.2% during June, July, August, September, October and November, respectively. In faecal cultures, there was difference (p<0.05) among animals treated with fungus was found in relation to the control animals during all the experiment month, with percentage reduction of 67.5%, 61.4% and 31.8% in September, October and November, respectively. Difference (p<0.01) was observed in the recovery of infective larvae from pastures that were collected up to 20 cm from the dung pats in pastures in the group treated with the fungus in relation to the control group with a reduction of 60.9% and between 0-20 and 0-40 cm from the faecal pat reduction (p<0.01) was about 56% in the group treated with the fungus M. thaumasium in relation to the control group pasture. There was no difference (p>0.05) between the average weight gains in both animal groups. The treatment of horses with pellets containing the nematophagous fungus M. thaumasium can be effective in controlling cyathostomin in the tropical region of southeastern Brazil.     

On the Natural Seeding of Marshland Pastures with Bovine Gastrointestinal Parasites

By placing parasite-free calves in paddocks grazed by infected animals for 18 day periods at various times during the previous season it was shown that eggs of Ostertagia ostertagi, Cooperia oncophora and Nematodirus helvetianus deposited on pastures from early July to October of one year were able to survive in the Maritime area of Canada over winter either as eggs and/or larvae and contribute to residual infections on these pastures the following spring. The greatest deposition and/or survival of those eggs that were shed on pasture occurred in August and September for Cooperia and in September and October for Ostertagia. Greatest deposition of Nematodirus occurred in July and August and relatively few Nematodirus eggs shed in late September or early October were infective early in the next season.

The number of generations of worms per year was low, ranging from one to two or perhaps three per year depending on the species. There was a delay in the maturation of many worm eggs.

Residual overwintering infections play a significant role in the establishment of initial infections each summer in susceptible stock. These animals recontaminate the pastures leading to the subsequent development of large numbers of infective larvae by late summer and autumn.

     

Strategic anthelmintic treatment of young cattle during summer in a Mediterranean-type climatic environment

A worm-control program utilising treatment of young grazing cattle with fenbendazole on two occasions during summer was tested in the Mediterranean-type climatic environment of south-west Western Australia. The grazing system aimed to produce steers by introducing three-month-old weaned calves to pasture in mid-winter until they were sold in early summer. Comparisons were made of the numbers of worm eggs passed on to plots by treated and untreated animals during autumn, the performances of treated and untreated cattle and the performances of calves introduced to the plots in mid-winter. The “tracer” calf technique was used to determine the availability of infective larvae on one untreated and one treated plot for each of the two years of the experiment.Treated animals deposited less Ostertagia spp. eggs on to pasture during autumn than did untreated animals in one of the two years. In both years they deposited less eggs of worm species other than Ostertagia spp. Less intestinal worms were acquired by “tracer” calves grazing treatment plots than those grazing no-treatment plots in both years, but there were no differences in the number of abomasal worms acquired.The reduction in availability of infective larvae of intestinal worms was insufficient to prevent the occurrence of parasitic gastroenteritis in calves introduced to the plots in mid-winter. The fenbendazole treatments did not confer any immediate body-weight advantage on treated animals.On both treatment and no-treatment plots, there were few infective larvae available to grazing cattle during early autumn, there was a rapid attainment of peak availability in winter and then a decline to low availability by mid-spring. In one year, infective larvae of intestinal worms (almost exclusively Cooperia spp.) increased in availability again in late spring and early summer. A high proportion of retarded worms was never a feature of the worm counts of “tracer” calves.It was concluded that the treatments may have been more effective had they been given during autumn.     

Predatory activity of the nematophagous fungus <Emphasis Type="Italic">Duddingtonia flagrans</Emphasis> on horse cyathostomin infective larvae

This work was performed to determine the predatory capacity in vitro of the nematophagous fungus Duddingtonia flagrans (isolate AC001) on cyathostomin infective larvae of horse (L₃). The experimental assay was carried out on plates with 2% water-agar (2% WA). In the treated group, each plate contained 1.000 L₃ and 1.000 conidia of the fungus. The control group without fungus only contained 1.000 L₃ in the plates. Ten random fields (4 mm diameter) were examined per plate of treated and control groups, every 24 h for seven days under an optical microscope (10× and 40× objective lens) for non-predated L₃ counts. After 7 days, the non-predated L₃ were recovered from the Petri dishes using the Baermann method. The interaction there was a significant reduction (p < 0.01) of 93.64% in the cyathostomin L₃ recovered. The results showed that the D. flagrans is a potential candidate to the biological control of horse cyathostomin L₃.     

Milk production and fatty acid profile of dairy cows grazing four grass species pastures during the rainy season in small-scale dairy systems in the highlands of Mexico

The study evaluated small-scale dairy systems with continuous grazing of pastures based on three temperate grasses festulolium (FL), tall fescue (TF), and perennial ryegrass (RG), compared with subtropical kikuyu grass (KG). All pastures were associated with white clover (Trifolium repens L.). Twelve multiparous Holstein cows were assigned to a 4?×?4 Latin square replicated three times with 14-day experimental periods. Sampling and analyses of pastures, concentrates, and animal variables followed standard procedures. FL showed a significantly (p?<?0.05) higher mean sward height, but there were no differences (p?>?0.05) in net herbage accumulation. There were significant differences (p?<?0.05) among pastures for CP, NDF, ADF, in vitro digestibility of OM (IVOMD), and estimated metabolizable energy (eME). There were no differences (p?>?0.05) between treatments for milk yield and composition, live weight, or body condition score. There were significant differences (p?<?0.05) in fatty acid values for pastures in C14:0, C16:1, and C18:3n3. There were significant differences between treatments (p?<?0.05) in milk contents for C18:0, C18:1t11, and C18:2c9t11. Grazing FL, TF, RG, or KY pastures showed no differences in milk yields. Higher values for C18:0, C18:1t11, and C18:2c9t11 were detected in KY, RG, and TF. RG had significantly higher MUFA than FL and higher PUFA than TF. A value under 65% of SFA, a ratio of n-6/n-3 lower than 4, and an atherogenic index of 1.7 are indicators of milk with beneficial effects for human health.     

Torque teno sus virus infection in suckling piglets from Brazilian pig herds

Torque teno sus virus (TTSuV) is responsible for the infection of pig herds around the world. The aim of this study was to analyse the presence of natural infection by both species of TTSuV in suckling piglets from major pig-producing regions of Brazil. Faecal samples (n?=?135) from 1 to 3-week-old suckling piglets from the Southern, Southeast and Midwest regions of Brazil were analysed by PCR assay to detect TTSuV1 and 2. TTSuV1 and 2 DNA was identified in 65 (48.1?%) and 23 (17?%) of piglet faecal samples, respectively. Co-infection by both species of TTSuV was detected in 17 (12.6?%) samples. Detection of TTSuV1 was significantly higher than that of TTSuV2 in the three Brazilian regions together (p?<?0.05). Based on age of animals, TTSuV1 infection was statistically higher than TTSuV2 in each age group (p?<?0.05). For all of the age groups together, no statistical difference was detected in the number of TTSuV1 and 2 positive results (p?>?0.05). These findings revealed that TTSuV infection has disseminated in pig herds from different geographic Brazilian regions, and the presence of TTSuV in suckling piglet faecal samples suggested the early infection by the virus and the potential of these animals in spreading the virus.     

In vitro predatory activity of nematophagous fungi <Emphasis Type="Italic">Duddingtonia flagrans</Emphasis> on infective larvae of <Emphasis Type="Italic">Oesophagostomum</Emphasis> spp. after passing through gastrointestinal tract of pigs

One isolate of predator fungi Duddingtonia flagrans (AC001) was assessed in vitro regarding the capacity of supporting the passage through pigs' gastrointestinal tract without loss of the ability of preying infective larvae Oesophagostomum spp. Fungal isolates survived the passage and were efficient in preying L₃ since the first 8 h of collection (p < 0.01) in relation to the control group (without fungus). Compared with control, there was a significant decrease (p < 0.01) of 59.6% (8 h), 71.7% (12 h), 76.8% (24 h), 81.0% (36 h), 78.0% (48 h), 76.1% (72 h), and 82.7% (96 h) in means of infective larvae Oesophagostomum spp. recovered from treatments with isolate AC001. Linear regression coefficients of L₃ of recovered Oesophagostomum spp. regarding the collections due to time were −0.621 for control, −1.40 for AC001, and −2.64 for NF34. Fungi D. flagrans (AC001) had demonstrated to be promising for use in the biological control of pig parasite Oesophagostomum spp.     

A Preliminary Study of the Biological Control of Strongyles Affecting Equids in a Zoological Park

The main goal in this research was to determine the beneficial effect of incorporating biological procedures in parasite control programs for equids in zoological parks. Two trials were developed for Equus quagga, E asinus , and E africanus asinus. The first trial (September 2010 to August 2011) consisted of chemotherapy only (ivermectin plus praziquantel), and the second trial (September 2011 to September 2012) consisted of administration of chemotherapy and chlamydospores of the nematophagous fungus Arthrobotrys (Duddingtonia) flagrans. The effect of these measures was evaluated by the estimation of the reduction in the fecal egg counts (FECR). In the first trial, 100% FECR values were achieved 15 days after treatment in all the animals. The egg reappearance period (ERP) was 2-3 months for the equids, and all of them were passing strongyle eggs in the feces at 2-4 months after their deworming. In the second experiment, the FECR values were 100% in the three species. ERPs of 3 months in the European donkeys, 4 months in the Africans, and 6 months in the zebras were recorded. All the equids had positive results for the coprological flotation test 4-8 months after anthelmintic administration. This preliminary study demonstrates the incorporation of chlamydospores of nematophagous fungus, as A flagrans appears highly promising for reduction of the infective stages of the strongyles affecting captive animals, but the experimental design precludes true determination of whether the treatment is fully efficacious.     

Effect of a single dry season anthelmintic treatment of N'Dama cattle on communal pastures in The Gambia

The effect of a single anthelmintic treatment of cattle during the early dry season was studied. One hundred and sixty-six N'Dama cattle, 1–3 years old, were selected from five herds. There were 65 males and 101 females divided into two groups of 83 animals each. One group was treated with fenbendazole at 7.5 mg/kg body weight by mouth in November 1992; the other group remained as the untreated control. At monthly intervals from November 1992 to April 1993, each animal was weighed and the number of eggs/g of faeces (epg) was determined. The infective larvae (L3) were examined following culture of pooled samples from each group of animals. In April 1993, 6 animals (3 treated and 3 controls) from the herds under study were necropsied. The difference in the weight gains (4.6 kg) of the two groups was highly significant (p<0.0001). The difference in the weight gains and the epg between the treated and control groups was influenced by the age of the animals. Of the treated animals, one contained no nematodes, one contained only 25Oesophagostomum radiatum, and the third contained 25Cooperia L4. The three untreated animals were all infected. It was concluded that the treatment in early dry season, with an anthelmintic effective against both adults and larvae, led to a significant reduction in egg counts, to elimination of adults and hypobiotic larvae and, consequently, to an increase in the body weight gain by the treated animals.     

Pilot project to investigate over-wintering of free-living gastrointestinal nematode larvae of sheep in Ontario,Canada

This study investigated the overwintering survival and infectivity of free-living gastrointestinal nematode (GIN) stages on pasture. The presence of GIN larvae was assessed on 3 sheep farms in Ontario with a reported history of clinical haemonchosis, by collecting monthly pasture samples over the winter months of 2009/2010. The infectivity of GIN larvae on spring pastures was evaluated using 16 tracer lambs. Air and soil temperature and moisture were recorded hourly. Free-living stages of Trichostrongylus spp. and Nematodirus spp. were isolated from herbage samples. Gastrointestinal nematodes were recovered from all tracer lambs on all farms; Teladorsagia sp. was the predominant species. Very low levels of Haemonchus contortus were recovered from 1 animal on 1 farm. The results suggest that Haemonchus larvae do not survive well on pasture, while Teladorsagia sp., Trichostrongylus spp. and Nematodirus spp. are able to overwinter on pasture in Ontario and are still infective for sheep in the spring.     

Grazing study in Ireland using the morantel sustained release bolus for controlling nematodiasis in calves

The morantel sustained release bolus was administered at turnout to first-season grazing calves in order to assess its efficacy in the seasonal control of infection by nematode parasites in Ireland. The pastures grazed by control calves showed a marked increase in gastrointestinal trichostrongylid infective larvae by September, while numbers of infective larvae on pasture grazed by bolus-treated calves remained at a low level throughout the grazing season. In consequence, the controls showed significantly higher worm egg counts in late season and significantly higher worm burdens (mainly Ostertagia spp) at necropsy carried out in November on representative number of principal animals selected from each group. These reduced worm burdens were attributed to the suppression of egg output during the early part of the season as a result of treatment with the morantel sustained release bolus at turnout in the spring. Pasture contamination with Dictyocaulus viviparus larvae was present on all treatment pastures. The bolus-treated calves however were subjected to an increase in D. viviparus infection which occurred on their pasture in late season after the active life of the bolus had expired. It was concluded that bolus treatment delayed (rather than prevented) the buildup of D. viviparus infection on the pasture by 60-90 days.     

Feasibility of herbage sampling in large extensive pastures and availability of cattle nematode infective larvae in mountain pastures

Herbage sampling has been used to ascertain the contamination and epidemiology of cattle nematode infective in large extensive pastures situated in the centre of France, where heifers graze for four months on a total area of one ha/heifer in mountains at 1200 or 1400 m above sea level. The sampling was done for each paddock in four virtual “hectares”, tufts of grass being picked both close to faecal pats or “refusals”, and far from these pats.Ostertagia was the predominant parasite and the occurrence of Dictyocaulus resulted from silent-carrier heifers. Just after the thawing of the snow, when the heifers arrived in the mountains, the contamination was very high: 8000–9000 L3 and 45.00 to 63.00 L3 kg^?1 dry herbage, respectively, far from and close to faecal pats, but this contamination decreases regularly during the season.The sampling of four areas (four “hectares”) in each paddock was found to be a very valuable method. The variation of the mean was low and found mainly when the number of larvae was high (6–19% only for the spring sampling).This technique could have some merit in parallel or concurrently with tracer calves which are always difficult and expensive to use.     

The development of the free-living stages of Strongyloides papillosus: I. Effect of temperature on the development of the heterogonic and homogenic nematodes in faecal culture

Temperature had a significant effect on the proportion of free-living females and infective larvae of Strongyloides papillosus developing from faecal culture. The number of free-living males recovered from cultures incubated at 20°C was fairly constant. However, females were most numerous at 30°C and infective larvae at 20°C, with the sum of the two approximately the same at both temperatures. This indicates that infective larvae and females are developing from genetically identical eggs. The critical period by which the course of development has been fixed occurs between 4 and 5 h at 30°C, but between 4 and 24 h at 20°C.     

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.     

Inhibited development of Obeliscoides cuniculi in rabbits: the effects of active and passive immunization and resumption of larval development

Rabbits were either actively or passively immunized against Obeliscoides cuniculi and challenged with 5 000 infective larvae (IL). Worm development was inhibited in actively immunized animals and worm egg production was impaired by administration of immune serum. Inhibited fourth stage larvae (L₄) from high-level infections (200 000 IL) and normal L₄ from low-level infections (4 000 IL) were transferred to actively immunized and normal rabbits. In both instances, large numbers of L₄ developed to maturity; however, a significant number of inhibited L₄ failed to resume development. Inhibition of larvae resulted in the development of fewer adult male than female worms, and the change in sex ratio was further accentuated in actively immunized recipients. Worm egg production was also reduced in actively immunized rabbits. These data indicate that host immune responses contribute to inhibition of O. cuniculi in rabbits and that worm egg production is also responsive to immunologic control.     

Response of young cattle to anthelmintic treatment during autumn in a Mediterranean-type climatic environment

A worm control programme in which heifers were treated with anthelmintic on three occasions during autumn, was tested in the Mediterranean-type climatic environment of south-west Western Australia. The experiment aimed to determine if the treatments would prevent the heifers contaminating their pastures with worm eggs during autumn, thereby improving their growth performances the following winter. An attempt was made to measure the availability of infective larvae of abomasal worms on the heifers' pastures during early winter by counting the worms in steers, previously of low worm status, that grazed with the heifers from late autumn until the start of mating in mid-winter.

The anthelmintic treatments reduced the contamination of pasture for most of autumn. The treated heifers that grazed these pastures grew faster, and by the start of mating two months after the last treatment were about 22 kg heavier, than untreated heifers grazing contaminated pasture. At the end of mating six weeks later the difference was 45 kg in favour of the treated heifers. At this time half the heifers grazing contaminated pasture were treated with anthelmintic. The following month these heifers grew faster than those left untreated, but by late November they had not attained the wieght of the heifers grazing uncontaminated pasture.

The heifers that grazed uncontaminated pasture produced more calves the following autumn than did those grazing contaminated pasture. The abomasal worm counts of the steers, with a mean of about 46 000 worms, failed to reveal any difference between treatments in the availability of larvae of abomasal worms on pasture. However, it was concluded that the treatments probably exerted their effect on growth rates by reducing the number of infective larvae ingested by heifers grazing the uncontaminated pasture during winter.