No description available.

No description available.

No description available.

Grazing cattle can be infected with a variety of gastrointestinal nematode species. In temperate regions, the most common of these species are considered to be the abomasal parasite, Ostertagia ostertagi, and the small intestinal dwelling nematode, Cooperia oncophora. Control of these nematodes is largely reliant upon the use of three anthelmintic classes: the benzimidazoles, imidazothiazoles and the macrocyclic lactones (ML). Worldwide, reports of anthelmintic resistance in cattle nematodes have increased in recent years; however, little information is available regarding this issue in farmed cattle in the UK. Knowledge is also lacking regarding anthelmintic usage practices, and whether or not the current methods used to detect anthelmintic resistance in cattle nematodes are robust and accurate. In this thesis, a number of approaches were taken to investigate these issues. A questionnaire study was conducted to evaluate anthelmintic usage and nematode control practices on a cohort of UK cattle farms. Descriptive analysis of the responses revealed that first season grazing calves were administered with anthelmintics, on average, twice per year (ranging between once and four times per year). It was also found that farmers depended heavily on ML products, with 80% of respondents administering a ML product in the previous 12 months and only 55% of respondents employing a quarantine treatment for cattle brought onto their farm. Faecal egg count reduction tests (FECRT) were then performed on 20 of the respondents’ farms, using injectable ivermectin (IVM). Two types of faecal egg count (FEC) methodology (a double centrifugation salt flotation method sensitive to one egg per gram and a McMaster method sensitive to 50 eggs per gram) were compared to investigate their utility in determining anthelmintic sensitivity of the derived nematode populations. A number of different statistical analyses were also performed to determine the optimum method of analysis for determining anthelmintic efficacy taking into account the effect of using arithmetic or geometric means, sensitivity of the FEC method and the effect of parametric bootstrapping. Of the 20 farms tested, 13 showed indications of inefficacy of IVM. Genus identification analysis of larvae derived from faecal samples obtained from the FECRT cohort indicated a minimum of 95% Cooperia spp. larvae in the post-treatment samples. Logistic regression analysis was also used to determine associations between management strategy on beef and dairy cattle enterprises and risk factors for IVM resistance. Farmers with dairy cattle were significantly less likely to use FEC (P = 0.013) or isolate new animals at quarantine (P = 0.013) compared to beef cattle farmers. Farmers who routinely monitored FEC were significantly less likely to use anthelmintics than those who did not monitor FEC (P = 0.042) and farmers who sought advice from their veterinary surgeons were less likely to administer anthelmintics according to the average weight of the herd (P = 0.02). Nematodes from two of the farms on which IVM resistance was indicated by the field FECRT were then further passaged and both isolates subjected to a controlled efficacy test (CET). Results from the CET confirmed the presence of IVM resistant C. oncophora (using two different application methods: injectable and pour-on administration), as well as the presence of moxidectin-resistant C. oncophora, the first confirmation in the UK. Analysis of phenotypic parameters was conducted on 679 female C. oncophora recovered at necropsy from all treatment groups. For both isolates, nematodes recovered from calves administered with moxidectin (MOX) pour-on anthelmintic were found to be significantly shorter than nematodes surviving IVM administration and nematodes from untreated control calves. Oviposition was also examined; with no eggs in utero found in any of the nematodes surviving MOX administration. Differences in the numbers of eggs in utero surviving IVM application were observed between the two isolates and also between application methods. Subsequently, analysis of a small section of a glutamate-gated chloride channel (glc-6) gene was conducted to investigate the presence of a single nucleotide polymorphism (SNP) in the glc-6 gene that had been previously proposed to be associated with ML resistance. This was achieved by comparing sequences derived from male and female C. oncophora (from both isolates) obtained from untreated calves with sequences from nematodes that had survived IVM administration. The SNP was not identified in any of the parasites analysed. Due to time and labour costs for conducting FECRTs for detecting anthelmintic resistance, a migration inhibition test was examined for its utility in assessing IVM sensitivity of third stage larvae (L3) derived from populations that had been demonstrated to have varying IVM sensitivity in vivo. Following optimisation, dose response curves and effective concentration (EC50) estimates were generated for all populations, including single species laboratory isolates of O. ostertagi and C. oncophora and mixed species isolates derived from the field studies above. The data failed to correlate with the previously obtained in vivo anthelmintic sensitivity classification for each isolate. Overall, O. ostertagi appeared to be less sensitive to IVM in the LMIT compared to C. oncophora, regardless of the ML sensitivity status of the isolate under study. Thus, these experiments indicated that the LMIT may have limited utility for assessing ML sensitivity of mixed species nematode isolates generated from field samples. In summary, the work in this thesis has found that UK cattle farmers heavily rely upon ML anthelmintics and there are clear differences in parasite control practices between farmers in the dairy and beef sectors, which may influence the development of anthelmintic resistance. As it is unclear when new classes of anthelmintics will become available for cattle, it is imperative to prolong the effectiveness of the current effective classes and to detect anthelmintic resistance as it emerges. This thesis has explored some currently available tools for the detection of ML resistance, with a view to improving them with appropriate best practice advice to help protect the health and welfare of cattle.

The studies within this thesis have made a valuable contribution to our understanding of anthelmintic resistance in Scotland and in particular to the prevalence of benzimidazole (BZ) and ivermectin (IVM) resistance, the expression of multiple resistance and its management. Parasitic gastroenteritis (PGE) is a major welfare issue not only for Scottish, UK and European farmers but also for livestock producers throughout the world. Parasites such as Haemonchus, Trichostrongylus and Teladorsagia are estimated to cost the sheep industry hundreds of millions of dollars annually. To date control has largely been achieved using anthelmintics, but over reliance on anthelmintics has led to the development of multi class anthelmintic resistance (AR) and the realization that intensive chemoprophylaxis is not a sustainable approach for the control of nematodoses. The first two papers contributing to this thesis assessed the prevalence of benzimidazole (BZ) and ivermectin (IVM) resistance within ovine gastrointestinal nematode populations in Scotland. The prevalence of BZ resistance in selected Scottish lowland sheep farms was around 24% in 1991 but this had risen to over 80% by 2001. The first cases of ivermectin resistance in sheep were only detected in 2001 but a small scale survey in 2004 showed that 35% of the farms (6 from 17) surveyed had IVM resistance, with Teladorsagia and Trichostrongylus being identified as the resistant genera. The isolation of a triple class resistant T. circumcincta (MTci5) population has enabled research to focus on the important issue of the therapeutic and prophylactic management of this emerging problem. The third and fourth papers detail a series of controlled efficacy tests conducted on MTci5 that confirmed, in the short term at least, it should be possible to use a milbemycin (moxidectin; MOX) or combination treatments, with IVM and one other class of anthelmintic to control nematodoses (>90% efficacy) caused by adult and/or immature worms. However the study examining larval susceptibility highlighted the important role that immature stages can play in the selection and transmission of resistance. Currently there are no tests that can detect the presence of these resistant larval stages. The fifth paper outlines parasitological findings from the farm where MTci5 was isolated following the confirmation of multiple class resistance. Substantial efforts were made to find solutions to maintain sustainability and profitability of the enterprise though ultimately the use of MOX selected for a, predominately Teladorsagia, population against which the persistent activity of the compound was only negligible with the reappearance of eggs in faeces occurring between 21 and 28 days post treatment. Effective sustainable control of AR populations not only requires an understanding of the phenotypic and genotypic mechanisms that underpin resistance but also improved means of ensuring that our farmers are made aware of and utilize identified best practice approaches. The written and verbal responses of the farmers to questions relating to best practice advice (papers six and seven) would suggest that many of the recommendations for delaying the selection and transmission of AR (ACME, Moredun Foundation and sustainable control of parasites of sheep (SCOPS), DEFRA) are not being followed, recommendations such as the effective quarantine treatment of newly purchased animals and dosing animals at the manufacturers’ recommended dose rate were followed by only 20% and 56% of farmers respectively.

Os parasitas nematóides afetam homens e animais, causando graves prejuízos à saúde pública e consideráveis perdas econômicas. A disponibilidade de anti-helmínticos de amplo espectro de ação tem auxiliado na redução de um grande número de perdas em decorrência das infestações parasitárias. Foram objetivos deste trabalho avaliar os efeitos do tratamento com moxidectina, na forma de longa-ação (LA), em sua dose terapêutica em touros, sobre a consistência e perímetro testicular, as características físicas (motilidade e vigor) e morfológicas do sêmen e o comportamento sexual. Foram utilizados 12 touros com idade de 48 ± 10 meses. Os animais foram alocados em 6 blocos com dois tratamentos. Os animais foram divididos nos grupos: controle (n=6), no qual cada animal recebeu 5 mL de solução fisiológica, via subcutânea, na orelha esquerda e grupo tratado (n=6), no qual cada animal recebeu 5 mL de moxidectina a 10% via subcutânea, na orelha esquerda. Os animais foram submetidos a exames andrológicos semanais, por um período de até 60 dias após o tratamento, sendo avaliadas as características testiculares (consistência e perímetro) e características seminais (motilidade, vigor e morfologia). Foram realizados testes de libido a cada 15 dias, num total de cinco testes. Os resultados obtidos indicam que não houve diferença significativa (P>0,05) para a consistência testicular, perímetro testicular, motilidade progressiva, vigor espermático, morfologia espermática e libido entre os touros dos grupos controle e tratado. Esses resultados indicam que o tratamento com moxidectina a 10% não influencia negativamente as características reprodutivas de touros. / The helminths affect human beings and animals, causing serious damage to public health and considerable economic losses. The availability of anthelminthic of a broad-spectrum has helped reducing a large number of losses due to parasitic infestation. The objectives of this work were to evaluate the effect of the treatment with moxidectin, in Long Action (LA) formulation, in therapeutic doses in bulls, on the testicular consistency and perimeter, physical characteristics (motility and strength) and morphological of the semen and sexual behaviour. Twelve bulls, age 48 ± 10 months used. These animals were put in six, 06 blocks with two treatments. The animals were divided in groups: Control group (n=6) each animal received 5 ml of physiological solution subcutaneously in the left ear, and Treated group (n=6) each animal received 5 ml of moxidectin at 10% subcutaneously in the right ear. The animals were submitted to andrological examinations weekly, within a period of 60 days after the treatment. The testicular characteristics (consistency and perimeter) and seminal characteristic (motility, strength and morphology) were evaluated. Libido tests were done every fortnight, in five tests all together. The results indicated that there were not significant differences. (P>0.05) for the testicular consistency, perimeter, progressive motility, spermatic strength, morphology and libido among bulls of the control and treated groups. These results indicated that the treatment with moxidectin at 10% does not influence negatively on the reproductive characteristics of the bulls.

Os parasitas nematóides afetam homens e animais, causando graves prejuízos à saúde pública e consideráveis perdas econômicas. A disponibilidade de anti-helmínticos de amplo espectro de ação tem auxiliado na redução de um grande número de perdas em decorrência das infestações parasitárias. Foram objetivos deste trabalho avaliar os efeitos do tratamento com moxidectina, na forma de longa-ação (LA), em sua dose terapêutica em touros, sobre a consistência e perímetro testicular, as características físicas (motilidade e vigor) e morfológicas do sêmen e o comportamento sexual. Foram utilizados 12 touros com idade de 48 ± 10 meses. Os animais foram alocados em 6 blocos com dois tratamentos. Os animais foram divididos nos grupos: controle (n=6), no qual cada animal recebeu 5 mL de solução fisiológica, via subcutânea, na orelha esquerda e grupo tratado (n=6), no qual cada animal recebeu 5 mL de moxidectina a 10% via subcutânea, na orelha esquerda. Os animais foram submetidos a exames andrológicos semanais, por um período de até 60 dias após o tratamento, sendo avaliadas as características testiculares (consistência e perímetro) e características seminais (motilidade, vigor e morfologia). Foram realizados testes de libido a cada 15 dias, num total de cinco testes. Os resultados obtidos indicam que não houve diferença significativa (P>0,05) para a consistência testicular, perímetro testicular, motilidade progressiva, vigor espermático, morfologia espermática e libido entre os touros dos grupos controle e tratado. Esses resultados indicam que o tratamento com moxidectina a 10% não influencia negativamente as características reprodutivas de touros. / The helminths affect human beings and animals, causing serious damage to public health and considerable economic losses. The availability of anthelminthic of a broad-spectrum has helped reducing a large number of losses due to parasitic infestation. The objectives of this work were to evaluate the effect of the treatment with moxidectin, in Long Action (LA) formulation, in therapeutic doses in bulls, on the testicular consistency and perimeter, physical characteristics (motility and strength) and morphological of the semen and sexual behaviour. Twelve bulls, age 48 ± 10 months used. These animals were put in six, 06 blocks with two treatments. The animals were divided in groups: Control group (n=6) each animal received 5 ml of physiological solution subcutaneously in the left ear, and Treated group (n=6) each animal received 5 ml of moxidectin at 10% subcutaneously in the right ear. The animals were submitted to andrological examinations weekly, within a period of 60 days after the treatment. The testicular characteristics (consistency and perimeter) and seminal characteristic (motility, strength and morphology) were evaluated. Libido tests were done every fortnight, in five tests all together. The results indicated that there were not significant differences. (P>0.05) for the testicular consistency, perimeter, progressive motility, spermatic strength, morphology and libido among bulls of the control and treated groups. These results indicated that the treatment with moxidectin at 10% does not influence negatively on the reproductive characteristics of the bulls.

No description available.

Gastrointestinal parasitism in grazing lambs adversely affects animal performance and welfare, causing significant production losses for the sheep industry. Control of gastrointestinal parasitism using chemotherapeutic treatment is under threat due to the emergence of anthelmintic resistance, thus stimulating research into alternative control strategies. Whilst investigating control strategies experimentally can be costly and time consuming, using a mathematical modelling approach can reduce such constraints. A previously developed model which describes the impact of host nutrition, genotype and gastrointestinal parasitism in a growing lamb, provided an appropriate starting point to explore control strategies and their impact on host-parasite interactions. Two contrasting mechanisms have previously been proposed to account for the occurrence of anorexia during parasitism. These were reductions in either intrinsic growth rate or relative food intake. Thus, the existing individual lamb model was modified to evaluate these mechanisms by exploring the relationship between anorexia and food composition (Chapter 2). For foods that did not constrain food intake, published data was found to be consistent with the predictions that arose from anorexia being modelled as a reduction in relative food intake. Reported genetic parameter estimates for resistance and performance traits appear to vary under differing production environments. In order to explore the impact of epidemiological effects and anthelmintic input on genetic parameter estimates the model was extended to simulate a population of lambs in a grazing scenario (Chapter 3). Whilst estimates of heritabilities and genetic correlations for drenched lambs remained constant, for lambs given no anthelmintic treatment, the heritability of empty body weight (EBW) reduced and the genetic correlation between faecal egg count (FEC) and EBW became increasingly negative with increasing exposure to infective larvae. Thus differences in anthelmintic input and pasture larval contamination (PC) may provide plausible causes for the variation in genetic parameter estimates previously reported. To investigate the interactions between host resistance and epidemiology (Chapter 4) a population of 10,000 lambs were simulated and FEC predictions used to assign the 1,000 lambs with the highest and lowest predicted FEC to ‘susceptible’ (S) and ‘resistant’ (R) groups, respectively. R and S groups were then simulated to graze separate pastures over 3 grazing seasons. The average FEC and PC predictions of these groups diverged during the first 2 grazing seasons and stabilised during the third, such that the difference in FEC predictions between R and S groups were double those predicted when grazed with the population. This was found to be consistent with experimental data. Further, anthelmintic treatment and grazing strategies were predicted to have no impact on the EBW of resistant lambs, suggesting that control strategies should be targeted towards susceptible animals. Targeted selective anthelmintic treatment (TST) has been proposed to reduce risks of anthelmintic resistance with minimal impacts on performance. To describe the short- and long-term impacts of TST and drenching frequency on sheep production and the emergence of anthelmintic resistance, the model was extended to include a description of anthelmintic resistance genotypes within the nematode population (Chapter 5). Reducing the proportion of treated animals was predicted to increase the duration of anthelmintic efficacy, whilst reducing the drenching frequency increased the long-term benefits of anthelmintic on sheep production. Various determinant criteria for use in TST regimes were compared (Chapter 5) including performance traits such as live weight and growth rate, and parasitological traits such as FEC. Using FEC as the TST criterion was predicted to allow the greatest reduction in the number of anthelmintic treatments administered whilst maintaining the highest average EBW, whilst live weight and growth rate were predicted to give little to no improvement in comparison to selecting animals at random for TST. Using estimated breeding values (EBVs) for FEC as the determinant criterion for TST regimes was compared to using measured FEC (Chapter 6). The EBV for true FEC across the entire growth period, akin to perfect genomic selection, was predicted to be a better criterion than measured time-specific FEC (including a sampling error) for a TST regime. EBVs calculated using measured time-specific FEC showed little benefit compared to measured FEC. The information gained from these simulation studies increases our understanding of control strategies and their impact on host-parasite interactions under various scenarios that may not have been possible using experimental methods. It is important to remember that the aim of alternative or complimentary control strategies is to maintain the sustainability of sheep production systems, and as such the production gain of any control strategy needs to be weighed against the financial, labour and time costs involved in implementation.

There is a pressing need to develop strategies to reduce the emergence of macrocyclic lactone anthelmintic resistance in sheep flocks. Management practices aimed at maintaining anthelmintic susceptible nematodes in refugia while achieving a satisfactory level of production may prove to be useful. However, sensitive molecular tests are required to monitor the subtle effects of these practices on the frequency of resistance alleles within nematode populations. To-date, conventional studies of candidate genes coding for the known methods of action of macrocyclic lactone anthelmintics have produced a complex picture, highlighting the relevance of different approaches to the identification of resistance markers. This thesis describes the development of a single nematode parent genetic crossing method and discusses its application to identify molecular markers for anthelmintic resistance. Parasitological and molecular verification of successful inbreeding of the MHco3 strain of H. contortus derived from the progeny of a genetic cross between single nematode parents is described. The single parent genetic crossing method has enabled the production of diverse inbred lines of the MHco3 H. contortus and may prove useful for genome assembly, or for the development of a genetic map. The study has afforded insights to the biology of H. contortus and effects of host immunity on nematode parasites. New information is presented concerning the period during which adult female nematodes continue to shed fertilised eggs after removal of males, the development of unfertilised H. contortus eggs, and the population genetics of mixed infections of two different strains of H. contortus. Novel backcrossing experiments initially between a macrocyclic lactone resistant (MHco4 or MHco10) and a susceptible (MHco3) strain of H. contortus and then between ivermectin treated backcross generations and the parental susceptible strain are described. The resources provided by these experiments should enable comparative genomic analysis and conventional molecular biology to identify resistance genes derived from the parental resistant strains in fourth backcross generations that are the same as a parent ivermectin susceptible population, apart from the presence of alleles linked to anthelmintic resistance, derived from parent resistant strains.