Characterising gastrointestinal nematode populations and anthelmintic resistance in Scottish dairy calves

Campbell, Paul Budge (2025) Characterising gastrointestinal nematode populations and anthelmintic resistance in Scottish dairy calves. PhD thesis, University of Glasgow.

Abstract

Gastrointestinal nematode (GIN) infections are ubiquitous in pasture-based grazing systems in the UK and worldwide, and are detrimental to animal health, welfare, and the productivity of livestock systems. These infections comprise coinfections with multiple species within a single host(s). Helminth species vary in epidemiology, pathogenicity, and anthelmintic sensitivity; however, the interactions among these parasites and the influence of management practices remain poorly understood. The most economically and clinically important GIN species infecting cattle in Europe are the abomasal parasite Ostertagia ostertagi and the smallintestinal-dwelling Cooperia oncophora, with the former being the more pathogenic.

To date, the control of GIN infections has primarily been achieved using three anthelmintic classes: benzimidazoles, imidazothiazoles, and macrocyclic lactones (ML), but over-reliance on treatment has inevitably resulted in the development of resistance. Although resistance in GIN of cattle appears to be developing more slowly than in nematodes infecting small ruminants, reports of resistance in the literature are increasing, suggesting an escalating problem.

For this reason, there is a pressing need to conserve anthelmintic efficacy and develop sustainable control measures. However, recommendations for sustainable parasite control in cattle are often extrapolated from sheep-based research, as cattle-specific research is inherently more challenging. The lack of sensitive tests for anthelmintic resistance limits research and surveillance. The purpose of this thesis was to advance understanding of the GIN communities infecting cattle on Scottish dairy farms, with a particular focus on characterising species composition and assessing anthelmintic resistance status. In vivo, in vitro, and molecular diagnostic approaches were used to characterise the GIN populations, and a genome-wide association study was used to identify genomic regions under ML selection within Os. ostertagi field populations. A longitudinal study examining the influence of management practices and anthelmintic treatment demonstrated that many of the established patterns of the most clinically important GIN species of cattle remain consistent when assessed using modern molecular techniques, despite the passage of fifty to sixty years and substantial changes in dairy farming practices since the original empirical studies.

The faecal egg count reduction test and egg hatch test highlighted the complexities involved in interpreting resistance tests, particularly with mixed species communities. These tests underscored the need for clearly defined criteria and thresholds if these methods are to be applied reliably in the field. Finally, the forward genetic approach identified a novel QTL associated with ML resistance on chromosome 5. The detection of this QTL in a major cattle parasite is the first major step toward understanding the genetic basis of ML resistance and will be used to advance our understanding of resistance in the field.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Supported by funding from the James Herriot Scholarship.
• Subjects: S Agriculture > SF Animal culture > SF600 Veterinary Medicine
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
• Funder's Name: James Herriot Scholarship
• Supervisor's Name: Ellis, Dr. Kathryn and Laing, Dr. Rosalind
• Date of Award: 2025
• Depositing User: Theses Team
• Unique ID: glathesis:2025-85646
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 11 Dec 2025 10:47
• Last Modified: 11 Dec 2025 10:50
• Thesis DOI: 10.5525/gla.thesis.85646
• URI: https://theses.gla.ac.uk/id/eprint/85646

Related URLs

• Article DOI
• Pre-print
• Article DOI