Gastrointestinal nematode infections in adult dairy cattle

Gastrointestinal (GI) nematode infections are present on all pasture-based cattle farms. The most important species in temperate climate areas are Ostertagia ostertagi and Cooperia oncophora. Infections with these species are an important cause of economic loss on farms throughout the world. The losses are mainly caused by clinical disease or reduced growth rates in young animals and milk yield losses in adult cows. The negative effect of GI nematodes on production are ascribed to a reduction in voluntary feed intake and the energy and amino acid requirements of the immune response raised against these infections. Milk yield responses to anthelmintic treatment in pastured dairy herds vary from no effect to responses to >2 kg/cow per day. Treatments can be targeted to animals with an expected production response based on evaluation of local (grazing) management practices and the measurement of O. ostertagi-specific antibodies in milk samples, which provides information on the level of larval exposure and an indication of the associated production losses. Control relies on anthelmintic treatment and grazing management, which should be used complementary to each other. The three critical factors that need to be considered when developing an anthelmintic control strategy in adult cows are the unpredictability of the treatment response, the timing of treatment and the risk for developing anthelmintic resistance