Nematode control practices and anthelmintic resistance in dairy calves in the south west of England

Abstract

A postal survey of worming practices on West Country dairy farms was undertaken and farmers were requested to send faecal samples for nematode egg counts. The majority of the farmers who responded had a nematode control policy which was based on a mixture of anthelmintics and pasture rotation. Sixty-five per cent turned out calves on to the same paddock each year and 57 per cent treated their stock with anthelmintics during the second year. Ninety farms submitted samples for analysis but only 16 samples contained sufficient eggs to justify repeat egg counts and only eight of these produced enough eggs for in vitro tests. The small number of positive samples, even into the latter part of the year suggests a heavy use of anthelmintics with relatively clean pasture. One Somerset farm had larvae which developed in high concentrations of ivermectin, and eggs were still being passed after two treatments with ivermectin at the manufacturer's recommended dose seven days apart. Of 100 male nematodes isolated from two of the calves, 88 were Cooperia species and 12 were Nematodirus species. A controlled trial with this isolate in eight Friesian male calves showed a 44 per cent reduction in egg counts at day 7 but no significant reduction in worm burden postmortem. This is the first reported case of ivermectin-resistant Cooperia species in cattle in the United Kingdom.

Sheep and goat nematode resistance to anthelmintics: pro and cons among breeding management factors

“…Cases of anthelmintic resistance have been recorded more and more often, threatening small ruminant breeding [30,77] and cases are also emerging in cattle [26,29,73,90,97]. Although many studies have enlightened the molecular basis for resistance to diverse anthelmintic families, reviewed by Sangster [81], few literature data are available concerning the factors responsible for anthelmintic resistance.…”

The role of targeted selective treatments in the development of refugia-based approaches to the control of gastrointestinal nematodes of small ruminants

“…Although it appears to be less of a problem in cattle, there have been reports of resistance from England (Stafford and Coles, 1999), New Zealand (Pomroy, 2006) and South America (Soutello et al, 2007;Suarez and Cristel, 2007) in cattle herds, and thus it is likely to become Anthelmintic resistance is recognised as a major problem affecting small ruminant production worldwide and now threatens the sustainability of many of these systems. One method that has been proposed to prolong the efficacy of our current anthelmintics is the maintenance of a parasite population in refugia (unexposed to a drug) which will maintain the genes for susceptibility within the parasite population.…”

Cattle nematodes resistant to anthelmintics: why so few cases?

“…Williams et al [39] found lower than expected activity of albendazole, fenbendazole and oxfendazole against immature and adult O. ostertagi suggesting some resistance. There were no cases of anthelmintic resistance in bovine nematodes in the UK when a survey was begun in 1998, but that work found the first case of ML resistance reported in the northern hemisphere [33]. Interestingly in this case the poor condition of the cattle had been attributed to coccidiosis as the animals had been treated with anthelmintic.…”

“…In addition there is not much information on the way farmers are using anthelmintics in cattle under different management conditions. Such information as is available suggests that farmers will be tending to over treat and thus select for resistance [33,36].…”

“…Coles nematodes using PCR probes to confirm whether there are any resistant worms in 'fully susceptible' populations. The micro agar larval development test (MALDT) can be used in cattle [33] but the optimum conditions have not been determined and the delineating doses are not known. Temperatures may need to be below room temperature.…”