Investigating anthelmintic control failures

Results:

All the 19 farms in the study used macrocyclic lactone products either in injectable (31%) or pour-on (69%) form.

Samples submitted for FEC from 19 farms:

• 24 submissions had FEC <100epg
•  8 submissions had FECs between 100 – 480epg

Wormer Tests performed on only 5 farms:

• 3 farms with FEC>100 epg pre-treatment
• 2 farms with low pre-treatment FEC (<100 epg)
• 3 farms had an efficacy >95% (range 96-100%)
• 2 farms had an efficacy of <95%
•  91% reduction (110 to 10 epg) – ML Injection
•  17% reduction (118 to 98 epg) – ML Pour on
• Both 100% Cooperia spp. In larval cultures post-treatment
• Both weighed animals and calibrated dosing equipment

Whilst few treatment failures were reported during the study period, those investigated indicated that suspect failures were generally associated with possible under dosing with pour-on ML products because of failure to estimate bodyweights correctly or not maintain or calibrate equipment. On one farm, where treatment only reduced the FEC by 17%, all the surviving eggs were identified as Cooperia spp., suggesting some selection for AR.

Planned activity:

Abstract to be presented at veterinary conference in York, March 2010.

Information used to support KT emphasising need for best practice when using anthelmintics.

The Problem:

Previous studies have highlighted that some anthelmintics are not sufficiently effective in cattle to control endoparasites sufficiently well. The cause for these control failures are not known. Poor application practice may be to blame, but it is possible that cattle worms may be developing resistance to anthelmintics as is the case with sheep worms. Either way control failures are an important issue for the industry and warrant further independent investigation.

Project Aims:

1. To investigate suspect anthelmintics treatment failures in cattle and determine causes
2. To investigate potential or suspect anthelmintics resistance using current methods described under WAAVP guidelines
3. Develop guidelines and protocols for investigating anthelmintic treatment failures and for determining the presence of AR in cattle nematodes

Approach:

Working with pharmaceutical companies and private veterinary surgeons to investigate suspected treatment failures. Farm investigations will be undertaken to determine possible causes of treatment failure. Wormer Testing (WT) will be used to clarify status of those farms and Faecal Egg Count Reduction Tests (FECRTs) also carried out on selected farms where the WT and treatment history are suggestive of the presence of anthelmintic resistance. It is proposed to undertake WT on a minimum of 50 farms, taking both pre- and post-treatment FEC. The timing of the 2^nd FEC will either be at 7 days for levamisole-based products or 14 days for benzimadazole or macrocyclic lactone products.