The Faecal Egg Count Reduction Test (FECRT) has been the mainstay for diagnosing anthelmintic resistance (efficacy lower than 95%) in the past 40 years and recent refinements have made it cheaper and more convenient. The World Association for the Advancement of Veterinary Parasitology has re-defined the test to allow before and after testing (instead of an untreated control group) and ’90 eggs observed’ in the control count the new standard. Using more sensitive methods such as Mini-FLOTAC or FECPAKG2, or even repeated counts using a McMaster worm egg chamber, the starting worm count can confidently be lowered to 1-200 epg, as long as sufficient numbers of sheep are included in the test.
The efficacy of all single active products against Haemonchus and Teladorsagia is low enough to warrant always recommending using active ingredients in combination. This can be achieved by concurrent administration or by using formulated combination products, but not by mixing products unless specifically allowed on the label. Long-acting single-active treatments such as moxidectin injectable need to be ‘primed’ with an effective drench.
Trichostrongylus continues to show susceptibility to the macrocyclic lactones, but BZs and levamisole have low efficacy. Nematodirus spp. eggs have shown up in groups of sheep treated with BZs , an indication of emerging resistance to this active ingredient.