WP 2 - Innovative strategies for the control of nematode infections in cattle: Targeted Selective Treatments (TST)

Introduction

A prerequisite to identify herds affected by parasites and then to treat only those animals that suffer from clinically significant parasitism (according to TST) is access to diagnostic tools that can be included in surveillance programs. By performing faecal egg counts (FEC) it currently only is possible to determine which individuals contribute most to the contamination of the pastures. Although FEC is a rather simple diagnostic method, it is both laborious and costly to perform. However, a more important disadvantage of FEC is the absence of a threshold FEC value between ‘sub-clinical’ infections with reduced weight gains and ‘subclinical’ infections without production losses. The first problem therefore is to identify good diagnostic biomarkers for parasitic infections that cause production losses and that can easily be applied on the farm. Using these markers, the efficacy of TST regimes for cattle will be monitored.

Objectives

To evaluate techniques for herd/individual health monitoring and TST aimed at reducing the use of anthelmintics in cattle.

Justification

The rationale for monitoring nematode infections is either: 1) prospectively to determine which control programme to use, or 2) retrospectively to determine the level of infection to which animals have been exposed and to evaluate the effectiveness of the applied control programme. For optimal control, First Season Grazing (FSG) calves exposed to excessive levels of gastrointestinal (GI) nematode challenge in their first grazing season (overexposed) may need more appropriate control measures in the second. However, often FSG calves are treated excessively, which may result in an insufficient development of immunity (underexposed). This leads to an increased susceptibility during the second grazing season. The level of serum pepsinogen, which is a direct indicator of the clinical damage caused by the abomasal worm Ostertagia ostertagi (the most pathogenic nematode of cattle in temperate regions), will be used to estimate the level of exposure to infection.

Recently, there has been an increase in the use of anthelmintics in dairy cattle due to the evidence that gastrointestinal nematodes can have a negative impact on milk yield and the development of anthelmintic drugs with a zero-withdrawal time for milk. Control of GI nematodes in dairy cattle can only be justified when milk production is affected. Recently, it was demonstrated that an O. ostertagi ELISA on bulk-tank milk is a promising diagnostic tool that can be used on a regional scale to identify dairy herds where the infection level with GI nematodes is likely to reduce productivity. Thus, it is likely that this ELISA can be used to identify risk factors associated with high infection levels and to determine when infection levels may justify control due to interference with productivity. In many EU countries, milk samples are tested for other infectious diseases like brucellosis, leucosis, bovine viral diarrhoea and bovine herpes virus. Consequently, an advantage of having a test based on milk samples is that it can then be incorporated in general herd health surveillance programmes.

For beef cattle, until now no practical methods have been developed to measure changes (= decline in production) due to nematode infections. Non-invasive techniques such as live-weight gains and body condition scoring will be evaluated to determine their value in identifying the most heavily infected individuals in flocks of FSG cattle.

Expected results

WP 2 will critically examine various key factors that will assist in the decision-making, i.e. whether a herd or animal requires treatment or not and/or which grazing management strategy needs to be put into operation. To determine the success of these TST orientated control measures, production parameters will be utilized. This will be compared to the recommended and widely applied strategies of worm control, which currently are based on strategic prophylactic mass treatment in the total group of FSG calves. One key issue for the implementation of TST by the end user is to demonstrate that TST does not negatively affect livestock productivity.

Organization

The partners involved in WP 2 are Ghent University (WP leader), University of Bristol, University of Veterinary Medicine Hannover, Swedish University of Agricultural Sciences, Svanova Biotech AB as well as Fraenz & Jaeger GmbH.