Cattle helminth infections in England and Wales: an investigation into prevalence, risk factors, attitudes and impacts

Abstract

Worldwide, there is an increasing demand for food, especially meat and milk. Alongside concerns around sustainability and other issues such as animal welfare, high expectations are put on livestock systems for an increased production and efficiency in order to meet such a demand. Helminth infections are ubiquitous on cattle farms and represent a growing concern for the industry around the world. In the UK, Ostertagia ostertagi and Fasciola hepatica are recognised as parasites of major importance in terms of their economic impact on cattle production and animal welfare. Rumen fluke is another strong candidate in the list of helminths which represent challenges for the sector in the UK. However, because helminth infections are mainly subclinical, their control is often very difficult. In this context, farmers generally adopt blanket treatment in young-stock to prevent or regain production losses due to these infections. This results in increasing problems of helminth resistance to available drugs, making such a practice unsustainable. Motivated by these concerns, several guidelines for best-practice on cattle helminth control have been published in the past few years. Nonetheless, farmers’ have been reluctant to adopt the recommendations put forward by these documents. Cattle helminths infections are influenced by the interplay of a wide range of factors. These include not only interactions between different species of parasites, but also climate conditions, management practices, availability of resources, and farmers’ attitudes, for which the role of comprehensive and reliable epidemiological information is key. An alternative to the use of cattle anthelmintic drugs is to avoid contamination of pasture to prevent the exposure of most susceptible cattle. The choice of diagnostic tools and the design of the studies are determinant for capturing the complexity of factors influencing helminth infections and control. However, basic epidemiological information on helminth infections in cattle in England and Wales is currently lacking, especially for O. ostertagi, F. hepatica and rumen fluke. Second, the relationship between economic losses and helminth infections remains to be clarified, particularly in the case of poly-infections and first lactation heifers. Third, previous studies informing potential alternatives (e.g. grazing management), suffer from limitations in terms of their scope and the adequacy of their recommendations. Finally, although being as relevant as epidemiological information, understanding what are the factors driving farmers’ decisions on cattle helminth control is a topic still poorly addressed in the literature. To address the issues above, this project was based on a mix-methods research (quantitative and qualitative methods) and a multidisciplinary framework that incorporates both veterinary epidemiology and sociology. The research analyses the cases of dairy and beef cattle in England and Wales by using longitudinal and cross-sectional studies, respectively. For dairy cattle, 43 farms (1,500 heifers) were studied. Data was collected and analysed in relation to the prevalence of O. ostertagi and F. hepatica; current practices in helminth control; demographics and management risk factors of young-stock helminth infections; impacts on milk production, reproduction and health performances in heifers; and farmers’ attitudes. As for beef cattle, data was collected for both single and poly-infections in 974 cattle (at slaughter), to support the analysis of the prevalence of O. ostertagi, F. hepatica and rumen fluke; demographic risk factors; and impacts on prime beef carcase performance. The main findings of this thesis are summarised below: Prevalence: the ubiquity of O. ostertagi and the significant presence of F. hepatica infections are confirmed; rumen fluke infections, most probably by C. daubneyi, can be considered as well-established in the UK; poly-infections by the three parasites are very common within the sample analysed; Risk factors: different types of grazing management practices can help with reducing dairy heifer exposure to O. ostertagi on pasture at specific times during their first years of grazing; Impact: the three parasites were significantly associated with low carcase performance in prime beef cattle; heifer exposure to O. ostertagi was significantly associated with lower milk production, reproduction and health performances; Farmers’ practices and attitudes: dairy farmers tend to overuse anthelmintic drugs on young-stock; they actively search and access information on cattle helminth infections and critically assess it in terms of management and business sustainability; farmers’ epistemology and contextual challenges should be taken into account while developing guidelines for helminth control. This thesis makes several contributions to veterinary and sociological studies of cattle helminth control. The different studies conducted shed light on a series of overlooked epidemiological and behavioural aspects that are critical for helminth control in the UK. Importantly, the thesis contributes to a better understanding of the complexity that is inherent to cattle helminth control. By considering both the epidemiology of the infections and broader societal and cultural factors, it offers a comprehensive analysis and a pioneer representation of how the system of cattle helminth control might operate in the UK. The results of this research are extremely valuable to veterinarians, farmers, experts, and policy-makers who all wish to develop and implement sustainable control of helminth infections in cattle