Diseases of Dairy Animals | Parasites, Internal: Gastrointestinal Nematodes

Abstract

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. Milk yield responses to anthelmintic treatment in recent studies on pastured dairy herds were around 1 kg per cow per day. The negative effects of GI nematodes on production are ascribed to a reduction in voluntary feed intake and the energy requirements of the immune response raised against these infections. GI nematode infections can be monitored based on O. ostertagi -specific antibody measurement, which provides information on the level of larval exposure and an indication of the associated production losses. Other diagnostic parameters are considered to be of limited use in adult cattle. Control relies on anthelmintic treatment and grazing management, which can 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.