A 4 year observation of gastrointestinal nematode egg counts, nemabiomes and the benzimidazole resistance genotypes of Teladorsagia circumcincta on a Scottish sheep farm

Anthelmintic resistance threatens the sustainability of sheep production globally. Advice regarding strategies to reduce the development of anthelmintic resistance incorporates the outcomes of modelling exercises. Further understanding of gastrointestinal nematode species diversity, and population dynamics and genetics (which may vary between species) is required to refine these models; and field studies combining faecal egg outputs, species composition and resistance genetics are needed to calibrate them. In this study, faecal samples were taken from ewes and lambs on a commercial farm in south-eastern Scotland at approximately 3 t-4 week intervals between spring and autumn over a period of 4 years. Faecal egg counts were performed on these samples, and L3 were collected from pooled coprocultures. Deep amplicon sequencing was used to determine both the species composition of these L3 and the proportions of benzimidazole-resistant single nucleotide polymorphisms in the isotype-1 β-tubulin locus of the predominant species, Teladorsagia circumcincta L3. Despite consistent management throughout the study, the results show variation in gastrointestinal nematode species composition with time and between age groups, that was potentially associated with weather conditions. The F200Y benzimidazole resistance mutation is close to genetic fixation in the T. circumcincta population on this farm. There was no evidence of variation in isotype-1 β-tubulin single nucleotide polymorphisms frequency between age groups, and no genetic evidence of reversion to benzimidazole susceptibility, despite targeted benzimidazole usage. This study highlights the need to include speciation when investigating gastrointestinal nematode epidemiology and anthelmintic resistance, and serves as an example of how genetic data may be analysed alongside species diversity and faecal egg counts, when markers for other anthelmintic classes are identified

A model for the control of psoroptic mange in sheep

No abstract available

Preliminary observations on the value of using effective anthelmintic drugs to control nematode parasitism in lambs in the face of a high level of infective larval challenge

Gastrointestinal nematode parasites in small ruminants pose a major challenge to global agriculture. In most cases, their control depends on the availability of anthelmintics, which must be used in a manner that achieves a balance between ensuring adequate productivity and minimising the impact of inevitable selection for drug resistance. In this observational field study, the liveweight gains of lambs grazed on putative heavily infective larval contaminated pasture were compared after effective or ineffective anthelmintic drug treatments. Moxidectin, monepantel, and a derquantel–abamectin combination achieved 100% post treatment efficacies in faecal egg count reduction tests, while the efficacy of levamisole against Teladorsagia circumcincta was only 33%. During the 14 days after treatment, lambs treated with moxidectin, monepantel, and a derquantel–abamectin combination, gained about 0.3 kg, 0.5 kg, and 0.7 kg, respectively, more than those treated with levamisole, generally supporting the economic investment in use of effective drugs. These observations serve to highlight the manner in which effective anthelmintic drugs are used most efficiently with the primary objective of minimising subsequent exposure of naïve lambs to high levels of infective larval challenge, as opposed to the more common practice of simply treating animals grazing on heavily contaminated pastures

On farm evaluation of the coproantigen ELISA and coproantigen reduction test in Scottish sheep naturally infected with Fasciola hepatica

The liver fluke, Fasciola hepatica, is a cause of significant economic losses in sheep farming. Lack of convenient and sensitive diagnostic tests in the live animal hampers the ability to monitor infection status and treatment efficacy. Use of a coproantigen ELISA and coproantigen reduction test, based on this ELISA, may address these issues but has, to date, only been evaluated in experimental challenge studies. We evaluated the coproantigen ELISA under working farm conditions in Scotland to assess its usefulness as a diagnostic test for liver fluke infection and as a diagnostic test to help determine the efficacy of flukicide treatment in sheep. First, liver fluke infection status was monitored longitudinally in a group of lambs, using monthly blood samples for biochemical assays and serum antibody ELISA and using monthly faecal samples for faecal egg count (FEC) and coproantigen ELISA. The average serum antibody ELISA titre became positive in September, two months ahead of faecal indicators of fluke infection. In contrast to results from experimental challenge studies, FEC and coproantigen ELISA became positive at the same time point. Secondly, treatment efficacy was measured in 100 ewes, from two farms, after treatment with triclabendazole (TCBZ) or closantel. Group level estimates of treatment efficacy were similar between faecal egg count reduction testing and coproantigen reduction testing at 7, 14 and 21 days post treatment. For individual animals, some inconsistencies between tests were observed. TCBZ treatment failure was noted on both farms, despite accurate weighing of animals and dosing of treatment products. We conclude that (1) coproantigen ELISA is a more convenient test than faecal egg counts and holds promise as a diagnostic tool for natural fluke infections in sheep but further evaluation of interpretation criteria may be needed; (2) the coproantigen ELISA has performed differently in the field compared with experimental challenge studies in sheep and (3) TCBZ-resistant fluke were present on both farms

Hepatogenous photosensitisation in Scottish sheep casued by Dicrocoelium dendriticum

Dicrocoeliosis was identified as the probable predisposing cause of weight loss and hepatogenous photosensitisation affecting half of a group of 14 month-old ewe lambs on a farm on the Inner Hebridean island of Coll. Oral dosing of the ewe lambs with 15 mg/kg albendazole only achieved a 79.2% reduction in Dicrocoelium dendriticum egg count, 21 day post treatment. Thus, this report of dicrocoeliosis differs from the disease that occurs elsewhere, both in the severity and nature of its clinical signs, and in the response of the parasite to anthelmintic drug treatment. These differences could indicate the existence of a genetically divergent D. dendriticum population, which may have evolved within the unique and isolated biotope afforded by the machair on the island of Coll. Better understanding of these factors is a prerequisite for effective and sustainable disease control

Addressing sustainable sheep farming: application of a targeted selective treatment approach for anthelmintic use on a commercial farm

Sustainable control of nematode parasites in small ruminant production is a worldwide ambition. Development of anthelmintic resistance can severely impair small ruminant production. A practical approach to reduce selection pressure for anthelmintic resistance is to treat only a proportion of the flock (Targeted Selective Treatment), leaving a proportion of the nematode population untreated. The aim of this study was to compare the sustainability and efficacy of a performance-based marker, the Happy Factor™, a monitor of nutrient utilisation efficiency, with a routine whole flock anthelmintic treatment. In a commercial flock in the South West of Scotland, 183 Texel cross lambs were split into two matched but co-grazing groups: one group managed as routinely for the farm (RT group) and the other subjected to targeted selective treatment (TST group). All lambs from the RT group were drenched every 6 weeks during the grazing season, while anthelmintic administration in the TST group was restricted to animals that failed to reach pre-determined weight gain targets, based on an estimate of their efficiency of gross energy utilisation. Animal performance and parasitological data were recorded every two weeks. In the 20 week period of the study, anthelmintic treatments were reduced by approximately 50% in the TST group compared to a routine anthelmintic administration that would have been applied, whilst epg counts were always <500 throughout the study in both groups. Finally, there was no discernible difference in the mean bodyweight gain between the two groups

Production impact of a targeted selective treatment system based on liveweight gain in a commercial flock

The sustainability of sheep production is hindered by anthelmintic resistance. Options to slow down or prevent resistance have been widely studied but their application in the field is still limited. In this study, the practical application and effect of a targeted selective treatment (TST) approach for the treatment of parasitic gastroenteritis was investigated in lambs (n = 385) over a 2 year period. At 14-day intervals during the grazing season, liveweight, breech soiling and anthelmintic treatments were individually recorded. Selection of lambs for anthelmintic treatment in the TST group was based on pre-calculated individual growth rates, with a matched cohort routinely treated (RT) with anthelmintic drug every 6 weeks. The adoption of a TST approach had no negative effect on the liveweight gains of the lambs, time to finishing or breech soiling measures compared to RT lambs; however a 50% decrease in anthelmintic treatment was observed in the TST group. The time to implement this system averaged 2 min per lamb. It is concluded that the TST could be suitable for commercial sheep farms, in association with automated weighing systems, potentially reducing selection for anthelmintic resistance, while having no negative effect on production