Anthelmintic Resistance In Sheep Research Articles

Investigation on parasite infection and anthelmintic resistance of gastrointestinal nematodes in sheep in Hinggan league (City), China

BackgroundDifferent areas of sheep infected with different types of parasites, all will cause serious harm to the local sheep, and the widespread use and repeated use of anthelmintics have produced different degrees of anthelmintic resistance (AR) in various regions. We re-investigated the infection of common parasites and AR of Gastrointestinal Nematodes (GINs) in sheep in Horqin Right Wing Front Banner, and first investigated the common parasite types and AR of GINs in sheep at other four areas in Hinggan league (city), China.ResultsA total of 1770 fecal samples were collected from 1 prefecture-level city and 4 counties in Hinggan league, in which the infection rate of Coccidia ranged from 83.3% to 96.06%, that of Ascaris ovis ranged from 10.17% to 15.19%, that of Moniezia benedeni ranged from 0.6% to 1%, that of Moniezia expansa ranged from 0.33% to 8.15%. The infection rate of GINs was 100%, and Haemonchus contortus was still the dominant species. The AR results showed that only the closantel in Horqin Right Wing Middle Banner was low resiatant, and the other three regions had been resistant. Levamisole also occurred AR in the other four regions, the widely used ivermectin and albendazole had produced serious AR in five areas. The research shows that GINs are becoming more and more resistant to various anthelmintics, which has made the problem worse.ConclusionsUnderstanding the dynamic changes of parasite infections and the development trend of AR in sheep in the region in this paper, the development trend seems to be more serious than imagined. Therefore only by deeply understanding the parasitic infections of sheep in this land can more reasonable medication guidance be carried out. It is expected to provide new ideas formore innovative, scientific and sustainable methods of preventing and controlling parasites.

An Overview of Anthelmintic Resistance in Domestic Ruminants in Brazil

Gastrointestinal nematodes (GIN) significantly, negatively impact livestock worldwide, and their control depends on the use of chemotherapy drugs. However, this approach is unsustainable as anthelmintic resistance (AR) is growing widespread. This article provides a comprehensive overview of the historical and current data published on AR in domestic ruminants in Brazil. Alternative measures of GIN control have been discussed to provide helpful information to prevent the development of AR in the country. This review consisted of a search of technical and scientific publications between January 1960 to January 2023, using online sources such as PubMed, Scielo and Google Scholar. Eighty-three articles published over the last six decades reporting AR in sheep (n = 43), goats (n = 20) and cattle (n = 20) were included. A total of 37.3%, 25.4% and 37.3% evaluated one, two and three or more molecule classes, respectively. Among all studies, 82.1% used fecal egg count reduction test as a method of AR diagnosis. In conclusion, AR is an urgent and emerging issue for ruminant production in Brazil. It is necessary to evaluate on a large scale the distribution and management of anthelmintic drugs and discuss strategies that delay this phenomenon’s development.

O-047 Anthelmintic resistance in sheep and goat: Results of faecal egg count reduction tests and associated risk factors

O-047 Anthelmintic resistance in sheep and goat: Results of faecal egg count reduction tests and associated risk factors

Anthelmintic resistance in sheep in the semiarid region of Minas Gerais, Brazil.

Anthelmintic efficacy was evaluated among sheep that had become naturally infected with gastrointestinal nematodes in 17 flocks located in the semiarid region of Minas Gerais, Brazil. Feces were collected individually from 1021 hairy sheep to determine the number of eggs per gram of feces (EPG) and for coprocultures to identify nematode genera the nematodes. Only the animals that presented EPG counts greater than or equal to 200 were included in the study (totaling 381 sheep). The animals were divided into three treatment groups: albendazole, ivermectin and levamisole. Fourteen days after the administration of anthelmintics, fecal samples were taken from all animals. In each flock, the pre-treatment and post-treatment arithmetic mean EPG were used to calculate the efficacy (FECR) for each of the treatment groups and the lower 95% confidence limit. Data were analyzed with the "eggCounts 2.3" package in RStudio, using a Bayesian model for paired design. The anthelmintics were classified as being efficacious (when the FECR was both equal to or above 95% and the lower 95% confidence limit was equal to or above 90%) or as encountering anthelmintic resistance (when the FECR was below 95% and the lower 95% confidence limit was below 90%) or inconclusive (when none of the other criteria were fulfilled). Albendazole and ivermectin were not effective in any of the flocks. Levamisole was effective against gastrointestinal nematodes in 25% of the flocks studied. Haemonchus, Trichostrongylus and Oesophagostomum genera were identified in this study in a semiarid region of Minas Gerais, Brazil. The genus Haemonchus was the most prevalent, followed by Trichostrongylus and Oesophagostomum. After anthelmintic treatment, the most prevalent genus was Haemonchus, followed by Trichostrongylus; the genus Oesophagostomum was not detected. The highest percentage of Haemonchus larvae was observed after treatment with ivermectin, followed by albendazole and levamisole. This study revealed the existence of gastrointestinal nematodes in sheep that present multiple resistance to all three main classes of anthelmintic drugs.

Detection of Anthelmintic Resistance in Sheep in and around Hassan District, Karnataka by Faecal Egg Count Reduction Test

Detection of Anthelmintic Resistance in Sheep in and around Hassan District, Karnataka by Faecal Egg Count Reduction Test

Risk factors associated with occurrence of anthelmintic resistance in sheep of resource-poor farmers in Limpopo province, South Africa.

Anthelmintic treatment is the most common way of controlling nematode infections in ruminants even though several countries have reported anthelmintic resistance (AR), resulting in limitation for sustainable small ruminant production. The aim of the present study was to evaluate the knowledge of resource-poor sheep farmers in Limpopo province of South Africa on the use of anthelmintics. A questionnaire regarding helminthosis control practices was administered to small ruminant farmers in five districts of Limpopo province namely Capricorn, Sekhukhune, Waterberg, Vhembe, and Mopani. A total of 77 resource-poor farmers were interviewed between June and August of 2017 using a structured questionnaire with a combination of qualitative and quantitative open-ended questions. The interviewed farmers were divided into three groups based on their farming experience (< 5; 6-10, and ˃10years of farming experience). Limited farming experience was shown as one of the risks, as farmers that owned sheep for less than 10years could not identify the symptoms of gastrointestinal parasites infection and did not know how nematodes are transmitted to animals. However, no significant difference (p < 0.05) was found to exist between the three groups of farmers in terms of clinical signs identification and correct application of anthelmintics. About 43% of the respondents were unaware of gastrointestinal nematodes (GI) that infect sheep, could not identify the clinical symptoms of gastrointestinal nematodes infection, and only 34% knew how animals become infected. Although 67.5% of farmers mentioned that they never dose their sheep, 32.5% use anthelmintics at varying times in a year. None of the farmers weighed their sheep before dosing them instead visual appraisal of individual weight was the most common means of estimating the anthelmintic dose. The above information is an indication of risks associated with possible occurrence of anthelmintic resistance in the study areas. There is therefore, a need to give training to resource-poor farmers of small stock on proper application of anthelmintic treatment and to educate them on how to prevent development of AR. Future studies on AR should also be conducted in the province in flocks with high-treatment frequencies to establish the occurrence of AR using both in vivo and in vitro methods. The most common risk factor associated with the occurrence of AR in all the five districts of Limpopo province was found to be the use of anthelmintics without weighing the animals to determine the correct dosage.

Detection of anthelmintic resistance in sheep and goat against fenbendazole by faecal egg count reduction test.

Anthelmintic resistance against commonly used anthelmintic fenbendazole was evaluated by employing faecal egg count reduction test (FECRT) in naturally occurring gastrointestinal (GI) nematodes in the semi organized sheep and goat farms of Ludhiana and Amritsar districts. A total of 80 animals (20 each for sheep and goat in both districts) were randomly selected and their faecal samples were examined by qualitative and quantitative parasitological techniques. Results indicate presence of high level of resistance against fenbendazole in both sheep and goat population of Ludhiana and Amritsar districts. More resistance was observed in the GI nematodes from animals reared in Amritsar district as compared to Ludhiana district. The level of anthelmintic resistance observed was apparently more in sheep than goats.

Survey of gastrointestinal menatodes and anthelmintic resistance in sheep and goats in communal grazing pastoral area, Yabello District, southern Ethiopia

A cross-sectional study was carried out from November 2013 to April 2014 in pastoral area, Yabello districts, to estimate the prevalence and to identify risk factors associated with gastrointestinal strongyle infection in sheep and goats. Moreover, to assess the anthelmintic resistance in goats gastrointestinal nematodes a total of 1040 faecal samples were collected (sheep, n=; 400 goats, n=640) of which 656 animals (63.1 %) were positive for strongyle eggs. Three-hundred three (75.8%) of sheep and 353 (55.2%) goats were positive for strongyle eggs .. Animal species and body condition influenced the prevalence of gastrointestinal parasite in sheep and goats in the study area. The mean EPG was significantly higher in female animals (x2 =4.02, P &lt; 0.05) and in local breed (x2 =3.89, P &lt; 0.05). The proportion of light level infection was higher followed by medium and heavy level of infection for species, sex, age, body condition and breeds of the study animals. The FEC reduction percentage for lvermectin, Albendazole and Tetramisole were 91.8%, 95.9% and 96.8%, respectively. Since the 95% confidence level lower limit for Albendazole and lvermectin were less than 90%, the gastrointestinal nematodes circulating in the area could be suspected to develop resistance for Albendazole and lvermectin. Hence, after further epidemiological study, strategic deworming and also animal health extension to create awareness of the sheep and goats owners regarding the impact of gastrointestinal parasites will play key role to reduce the higher prevalence of gastrointestinal parasites of sheep and goats in the study area.Keywords: EPG, Gastrointestinal, Sheep, Goat, Yabello, Ethiopia

A systematic review and meta-analysis of factors associated with anthelmintic resistance in sheep

BackgroundAnthelmintic drugs have been widely used in sheep as a cost-effective means for gastro-intestinal nematode (GIN) control. However, growing anthelmintic resistance (AHR) has created a compelling need to identify evidence-based management recommendations that reduce the risk of further development and impact of AHR. ObjectiveTo identify, critically assess, and synthesize available data from primary research on factors associated with AHR in sheep. MethodsPublications reporting original observational or experimental research on selected factors associated with AHR in sheep GINs and published after 1974, were identified through two processes. Three electronic databases (PubMed, Agricola, CAB) and Web of Science (a collection of databases) were searched for potentially relevant publications. Additional publications were identified through consultation with experts, manual search of references of included publications and conference proceedings, and information solicited from small ruminant practitioner list-serves. Two independent investigators screened abstracts for relevance. Relevant publications were assessed for risk of systematic bias. Where sufficient data were available, random-effects Meta-Analyses (MAs) were performed to estimate the pooled Odds Ratio (OR) and 95% Confidence Intervals (CIs) of AHR for factors reported in ≥2 publications. ResultsOf the 1712 abstracts screened for eligibility, 131 were deemed relevant for full publication review. Thirty publications describing 25 individual studies (15 observational studies, 7 challenge trials, and 3 controlled trials) were included in the qualitative synthesis and assessed for systematic bias. Unclear (i.e. not reported, or unable to assess) or high risk of selection bias and confounding bias was found in 93% (14/15) and 60% (9/15) of the observational studies, respectively, while unclear risk of selection bias was identified in all of the trials. Ten independent studies were included in the quantitative synthesis, and MAs were performed for five factors. Only high frequency of treatment was a significant risk factor (OR=4.39; 95% CI=1.59, 12.14), while the remaining 4 variables were marginally significant: mixed-species grazing (OR=1.63; 95% CI=0.66, 4.07); flock size (OR=1.02; 95% CI=0.97, 1.07); use of long-acting drug formulations (OR=2.85; 95% CI=0.79, 10.24); and drench-and-shift pasture management (OR=4.08; 95% CI=0.75, 22.16). ConclusionsWhile there is abundant literature on the topic of AHR in sheep GINs, few studies have explicitly investigated the association between putative risk or protective factors and AHR. Consequently, several of the current recommendations on parasite management are not evidence-based. Moreover, many of the studies included in this review had a high or unclear risk of systematic bias, highlighting the need to improve study design and/or reporting of future research carried out in this field.

Comparison of calculation methods used for the determination of anthelmintic resistance in sheep in a temperate continental climate.

This study compared results obtained with five different fecal egg count reduction (FECR) calculation methods for defining resistance to ivermectin, fenbendazole, and levamisole in gastrointestinal nematodes of sheep in a temperate continental climate: FECR1 and FECR2 used pre- and posttreatment fecal egg count (FEC) means from both treated and control animals, but FECR1 used arithmetic means, whereas FECR2 used geometric means; FECR3 used arithmetic means for pre- and posttreatment FECs from treated animals only; FECR4 was calculated using only arithmetic means for posttreatment FECs from treated and control animals; and FECR5 was calculated using mean FEC estimates from a general linear mixed model. The classification of farm anthelmintic resistance (AR) status varied, depending on which FECR calculation method was used and whether a bias correction term (BCT, i.e., half the minimum detection limit) was added to the zeroes or not. Overall, agreement between all methods was higher when a BCT was used, particularly when levels of resistance were low. FECR4 showed the highest agreement with all the other FECR methods. We therefore recommend that small ruminant clinicians use the FECR4 formula with a BCT for AR determination, as this would reduce the cost of the FECRT, while still minimizing bias and allowing for comparisons between different farms. For researchers, we recommend the use of FECR1 or FECR2, as the inclusion of both pre- and posttreatment FECs and use of randomly allocated animals in treatment and control groups makes these methods mathematically more likely to estimate the true anthelmintic efficacy.

Field investigation of anthelmintic efficacy and risk factors for anthelmintic drug resistance in sheep at Bedelle District of Oromia Region, Ethiopia

The study was conducted to investigate the status of anthelmintic (AH) efficacy and associated risk factors for AH resistance in sheep. Questionnaire surveys were undertaken to establish the AH utilization practices of sheep owners at the study area and identify risk factors. Four hundred fourteen sheep were sampled of which 180 sheep were selected based on their higher egg count for the fecal egg count reduction test (FECRT) to assess the efficacy of albendazole, tetramisole and ivermectin against gastrointestinal nematode parasites prevailing in sheep. Fecal culture and postmortem examination techniques were used to identify the species of nematode parasites prevalent before and after treatment. The results show that: 1) albendazole and tetramisole were the most frequently used AH in the area, 2) farmers get the drugs with or without prescription from various sources (10% open markets, 18% private drug stores and 72% government animal health clinics and 3) the prevalence of gastro-intestinal nematode infection in the study areas was 72%. 4) The FECRT revealed all the three tested AH were effective with egg count reduction levels of 96%, 99% and 97% respectively for albendazole, tetramisole and ivermectin. However, post-treatment fecal cultures and postmortem adult worm recovery showed that some Haemonchus contortus worms have escaped the treatments. In conclusion, no anthelmintic resistance was detected from clinical cure point of view but the population of H. contortus that has escaped the treatments deserves further scrutiny as this parasite is the most prolific and highly pathogenic in sheep.Key words: Anthelmintic efficacy, FECRT, Gastrointestinal Nematodes, Risk Factors, Sheep.

Anthelmintic resistance in sheep farms: Update of the situation in the American continent

The present paper reviews the frequency of anthelmintic resistance in sheep farms in different countries of the American continent and describes some aspects that might influence the trend in sheep farms. The situation of anthelmintic resistance in sheep farms has been explored mainly in south of the continent (Argentina, Brazil and Uruguay) where sheep farming is an important industry. In those three countries, as well as in Paraguay, the first comprehensive surveys of anthelmintic resistance were performed among countries in the continent, which showed evidence of high frequency of sheep farms with anthelmintic resistance. Today, it is common to find sheep flocks with multiple-resistant worms. In North and Central America, a similar situation has been reported in sheep farms in the south of the United States of America, parts of Mexico and Costa Rica. On the other hand, other areas of the continent show low frequency of farms with anthelmintic resistance. From many areas no results have been published regarding situation on anthelmintic resistance or, alternatively, published results have received limited dissemination. Although the diagnosis of anthelmintic resistance is important for decision making of helminth management/control at the farm level, this is still an aspiration rather than a reality. For decades, researchers working on anthelmintic resistance in the American continent have expressed the need to change farmers’ attitudes towards anthelmintic drugs. A common advice has been to check the anthelmintic drug efficacy regularly and reduce the dependence on these with alternative control measures. In spite of such advice, the challenge to stop/delay the advancement of anthelmintic resistance against the available anthelmintic drugs is still present. The evidence suggests that anthelmintic resistance is a growing phenomenon in the American continent. The situation described might be the tip of the iceberg, as anthelmintic resistance is still largely under-diagnosed. Hence, a different approach to tackle the advancement of anthelmintic resistance in sheep farms must be found. Awareness of farmers on the importance of diagnosis of anthelmintic resistance is not enough. Technical support schemes that provide the diagnostic service cheaply and timely must be implemented together with the research aiming at the adoption of control methods to reduce the dependence on conventional anthelmintic drugs. Unless these elements are readily available for producers, the negative consequences of anthelmintic resistance on sheep farming in America will continue to worsen with time.

Anthelmintic resistance in sheep in Europe: A selected review

Intensive use of anthelmintics to control gastrointestinal nematodes selects for anthelmintic resistance, which has become an important issue in many European countries. Presence of nematode strains resistant to benzimidazoles, imidazothiazoles and/or macrocyclic lactones has been repeatedly reported, particularly for the three most important genera, Haemonchus, Teladorsagia and Trichostrongylus. Additionally, multiple drug-resistant populations of these parasites have also been detected. Examples are given for the situation in European countries with differing climatic conditions and management systems of small ruminants. The widespread emergence of multi-resistant nematodes proves that the past intensive suppressive chemical control strategies may not be a successful approach any longer. Experience from the up to now development of anthelmintic resistance suggests that modern control schemes should not rely on sole use of anthelmintics, but employ other, more complex and sustainable recipes, combing chemical, environmental and immunological control.

SCOPS and COWS—‘Worming it out of UK farmers’

Infections with gastrointestinal roundworms are an important cause of production losses in sheep and cattle. Worm control is a vital part of health and production management in sheep flocks and cattle herds in the UK, and good control is highly dependent on effective anthelmintics. Unfortunately, a direct and unavoidable consequence of using anthelmintics to control worm populations is selection for individuals that are resistant to the chemicals used.If left unchecked, anthelmintic resistance (AR) could prove to be one of the biggest challenges to sheep and cattle production and animal welfare within the UK. As a consequence of increasing reports of AR in sheep, a working group, “SCOPS” (sustainable control of parasites in sheep) was formed in 2003 with representatives from the UK sheep industry to promote practical guidelines for sheep farmers and their advisors. This led to the production of guidelines for ‘sustainable worm control strategies for sheep’ intended for veterinarians and sheep advisors, plus ongoing promotional literature aimed at farmers.Whilst there is some evidence of emerging resistance in roundworms of cattle, it appears to still be at a very low level in the UK. However the potential presence of such AR in cattle worms has been seen as a timely warning, which if ignored, could lead to a not dissimilar AR situation to that seen in sheep, and in other cattle areas around the world. Reports of AR in UK cattle nematodes have generally been limited to a small number of anecdotal reports of treatment failure with some macrocyclic lactone (ML) products, especially those formulated as pour-on preparations, and invariably involving the dose-limiting species, Cooperia oncophora. As a consequence of these observations, guidelines have been produced similar to those for sheep, for sustainable worm control strategies for cattle “COWS” (control of worms sustainably), and were launched in May 2010. Uptake and effectiveness of SCOPS recommendations are currently being monitored in collaboration with the UK animal health industry, and similar proposals are being considered for uptake of COWS guidelines following the launch this year.

In this issue – June 2011

Computer model predictions and field observations of anthelmintic resistance in sheep · Dangers of off‐label use of barium selenate · Elbow luxation in dogs and cats · Prognosis of joint infections in adult horses · Omentalisation for mediastinal abscess in a dog · Adenoviruses in lizards

The production costs of anthelmintic resistance in sheep managed within a monthly preventive drench program

To determine the impact of anthelmintic resistance on the productivity of sheep grazed on pasture in a temperate climatic zone, 14 groups each of 20 lambs were grazed on pasture on which benzimidazole-resistant parasites had been detected previously, then treated every 28 days - seven groups with a benzimidazole anthelmintic (albendazole) and seven with monepantel, a member of a new anthelmintic action family which was assumed in advance to be completely effective in removing all established worms. Faecal egg counts and larval differentiation demonstrated the presence of albendazole resistance, predominantly in Teladorsagia circumcincta but also in Trichostrongylus spp. By days 84 and 112, egg counts were significantly higher in the albendazole-treated animals than in those treated with monepantel. The presence of anthelmintic resistance resulted in a reduction in live-weight of 2.8 kg, a significant increase in breech-soiling and a significant reduction in body condition score. Fourteen animals from each treatment were necropsied at a commercial abattoir and carcase weights and standard quality parameters recorded; there was a reduction in carcase weight of 2.8 kg in the albendazole-treated animals, and a difference in the carcase grades within each group. These measurements were used to calculate that the presence of anthelmintic resistance resulted in a 14% reduction in carcase value.

Resistência anti-helmíntica de nematóides gastrintestinais em ovinos, Mato Grosso do Sul

Entre os métodos de controle da verminose gastrintestinal em ovinos, a utilização de produtos químicos é o mais empregado. Porém, o uso indiscriminado e continuado desses produtos tem selecionado populações de helmintos resistentes aos anti-helmínticos, fenômeno relatado no mundo todo. Este trabalho teve como objetivo identificar as espécies de parasitos gastrintestinais e diagnosticar a situação da resistência anti-helmíntica em ovinos no Estado de Mato Grosso do Sul. Foram realizados testes de redução na contagem de ovos por grama de fezes (OPG) em rebanhos de dezesseis propriedades rurais; as sete formulações utilizadas continham as seguintes bases farmacológicas: Albendazol, Ivermectina, Levamisole, Triclorfon, Moxidectina, Closantel e uma contendo as três primeiras associadas. As espécies identificadas nas necropsias, em ovinos adultos, foram: Haemonchus contortus, Trichostrongylus colubriformis, Cooperia curticei, C. punctata, C. pectinata e Oesophagostomum columbianum; em ordem de prevalência. As formulações contendo Albendazol e Ivermectina não apresentaram eficácia na redução de OPG nos rebanhos testados, com médias de redução de 0,7 e -19,6%, respectivamente. Closantel apresentou eficácia média de 6,7%; Levamisole, Moxidectina e Triclorfon de 28,7, 26,8 e 65%, respectivamente; a associação das três bases (Albendazol, Ivermectina e Levamisole), uma média de eficácia de 55,8%. As percentagens médias de larvas infectantes recuperadas nas coproculturas, tanto no pré como no pós-tratamento, foram semelhantes; indicando que a resistência às bases testadas está presente em todas as espécies citadas, em maior ou menor intensidade. Os dois gêneros predominantemente resistentes são Haemonchus sp., com 86,9%; seguido por Trichostrongylus sp., com média de 47,5%; Strongyloides sp. 33,6%; Oesophagostomum, sp. 21,4% e Cooperia sp. 19,7%.

Anthelmintic resistance in sheep and goat farms on Peninsular Malaysia

The faecal egg count reduction test (FECRT) was conducted on 39 sheep farms and 9 goat farms located in Peninsular Malaysia. The anthelmintic groups used in these tests were the benzimidazoles, levamisole, the benzimidazole/levamisole combination, macrocyclic lactones and closantel. Results indicated that the prevalence of resistance to the benzimidazole group was high, with approximately 50% of the sheep farms and 75% of the goat farms having resistant nematode parasite populations present. Resistance to levamisole, closantel and ivermectin was also detected. Differentiation of the infective larvae derived from faecal cultures indicated that by far the most predominant parasite species was Haemonchus contortus.

Further studies on anthelmintic resistance in sheep at an organised farm in arid region of Rajasthan

Faecal egg count reduction test (FECRT) and in vitro egg hatch assay (EHA) was performed on Indian Karakul (3/4 crosses of Karakul with Malpura, Marwari and Sonadi) transported from arid region campus, Bikaner, where resistance was reported in 1996. FECRT revealed that fenbendazole and levamisole were 100% effective in reducing the egg counts. LC 50 value on EHA was 0.074 ± 0.015 μg thiabendazole ml −1. The faecal culture examination revealed the presence of Haemonchus contortus only. It was concluded that H. contortus was fully susceptible to both benzimidazole and levamisole.

Further potential limitations of the undifferentiated faecal egg count reduction test for the detection of anthelmintic resistance in sheep

Fifteen (36%) of 42 mixed gastro-intestinal nematode infections in sheep, identified as drench-susceptible by the undifferentiated faecal egg count reduction test, were found to harbour anthelmintic-resistant worms when analysed on the basis of changes in the egg counts of individual nematode genera. Most of these cases involved resistance in a single nematode genus, with Ostertagia and Trichostrongylus being implicated most frequently. The possible contributory role of larval culture results in helping to reduce the chances of the faecal egg count reduction test producing these and similar types of errors is discussed.