Parasite surveillance and novel use of anthelmintics in cattle

Background Cattle are economically the most important livestock for farmers in Sweden. However, both dairy and beef production has been subjected to considerable structural change over recent decades. Currently, there are approximately 1.5 million cattle, including ≈370 000 dairy cows producing milk worth 1 m€ [1]. The trend is that the numbers of dairy cows are decreasing slowly, while beef cows are somewhat increasing. At the same time as the productivity has been intensified since the 1950’s in the cattle sector, herd size has increased and the number of production units, especially the number of dairy farms, have been dramatically reduced. In contrast, the numbers of organic farms are steadily increasing. The goal of the Swedish government is to increase the Swedish organic production of agricultural commodities to 20% within a three-year period. According to the Swedish animal welfare regulations, both conventional and organic cattle must have access to pasture for a period of 2–3 months per year [2]. The grazing season normally occurs between early May and October. As pasture-borne parasites are ubiquitous wherever animals are grazing, they remain one of the most important productivity constraints in Swedish cattle production. These parasites have in common that they often exhibit simple direct life cycles with infective stages transmitted on pasture by the faecal–oral route. The most important pasture-borne parasites of grazing cattle in Sweden are the gastrointestinal (GI) nematodes Ostertagia ostertagi and Cooperia oncophora. To a lesser degree, the lungworm Dictyocaulus viviparus, and also the coccidian Eimeria alabamensis, are important pathogens. Furthermore, in wet areas the liver fluke Fasciola hepatica, with a complex life cycle, sometimes cause problems. The importance of GI-nematodes and lungworms on the productivity in first-season grazing (FSG) cattle has been demonstrated in a range of independent grazing trials conducted at SWEPAR over the last decade [3-8]. According to the results, the weight-gain penalties in unprotected set stocked FSG animals were on an average in the range of 20 to 65 kg, compared to simultaneously grazed calves but that were fully protected from parasites by the use of effective anthelmintics. Combined, these trials demonstrate the importance of nematode parasites on animal productivity under Swedish climatic and management conditions. They also show that good levels of nematode control can be achieved through the correct use of anthelmintics. However, at the same time there are concerns that over-dependence on ‘chemical’ control may lead to long-term difficulties. This occurs partly through development of anthelmintic resistance, but also because these substances are not widely accepted among consumers. Routine prophylactic use of anthelmintics is not accepted in organic livestock farming [9]. However, “blanket” treatment of the whole grazing group or herd is accepted, even on organic farms, in response to a worm problem after it has been diagnosed. Although the results from our grazing trials also have shown that good levels of parasite control can be achieved without anthelmintics, some of the alternative non-chemical parasite control approaches that we have tested are impractical. For example, when it comes to the use of natural pasturelands there are situations where high grazing pressure must be maintained in order to maintain a profile necessary for the generation of subsidies. Young and adult stock on Swedish dairy Department of Biomedical Sciences and Veterinary Public Health, Div. of Parasitology and Virology (SWEPAR), Swedish University of Agricultural Sciences (SLU), SE-751 80 Uppsala, Sweden Höglund Acta Veterinaria Scandinavica 2010, 52(Suppl 1):S25 http://www.actavetscand.com/content/52/S1/S25