Ecology/Physiology Workgroup Nematode Parasites and Grazing Research

Parasitism, and gastrointestinal nematode parasitism in particular, is arguably the most serious constraint affecting ruminant production world-wide. Economic losses are caused by decreased production, cost of prophylaxis, cost of treatment, and the death of infected animals. It is difficult by any form of major survey or other estimation to establish precise figures on losses incurred in production from infection and disease. Even minimal accuracy of loss estimates is difficult because production diseases or disorders may result from interaction with nutritional and environmental stresses, management methods, concurrent diseases, genetic predispositions, or other factors. Periodic reports on such losses from governmental agencies and others, always range into millions of dollars per year and include all phases of production. Problems with nematode parasitism are often classified as production disease (i.e. chronic subclinical condition affecting productivity such as weight loss, reduced weight gain, reproductive inefficiency, etc.). The unique thing about nematode parasitism, compared to other infectious diseases, is that the host is almost always associated with some level of infection year round whereas other infectious diseases usually come and go. Therefore, nematode parasitism continually affects production, and other infectious diseases affect production sporadically. Because nematode parasites are associated with all grazing animals, it is important to understand the parasites involved, how infection might affect results and how to control parasites to minimize parasite effects on grazing research. For an overview of these parasites, appropriate sections in well recognized and used textbooks can be referenced (Dunn, 1980; Urquhart et al., 1996; Bowman and Georgi, 2002).