Issues and tools for an evidence-based use of treatments against gastrointestinal nematodes in cattle and small ruminants

Abstract

In grazing ruminants, gastrointestinal nematode (GIN) infection can induce production losses, even clinical disease in non-immunized animals. Control measures essentially rely on anthelmintic (AH) treatments, applied frequently and without prior assessment of the effective parasitological risk. This review aims firstly at putting forward the main risks related to this non rational use of AH: emergence of drug-resistant parasitic populations, ecotoxicity on the microfauna involved in feces degradation on pastures, and delayed development of immunity against GIN (particularly in cattle). Targeted-selective treatment strategies should put such risks under control, while preventing clinical disease and securing productions. AH treatment would be rationalized by targeting herds/flocks, groups and periods with a parasitological risk, and by selecting the less resistant/resilient animals. Thus, this review aims secondly at describing the tools and indicators studied to implement such strategies: production-based indicators (daily weight gain, parity, level of production…), clinical indicators (FAMACHA©, diarrhea index…), parasitological indicators (coproscopy, anti-GIN antibody level…), or indicators based on grazing management, and software tools (simulation model of the pasture infectivity level). Their reliability and operationality are variable. The implementation of these innovative strategies is a paradigm shift with respect to current practices, and requires the lowering of acceptance barriers. Such a rational use of AH would ensure the sustainability of control measures against GIN infection in ruminants.