Gastrointestinal Parasites: a Frequently Underestimated Constraint on Production of Grazing Animals

A knowledge of parasitism in grazing animals is needed to properly understand and manage grazed ecosystems. This paper focuses on effects of gastrointestinal (GI) parasites in beef cattle. These parasites have both clinical and subclinical effects on animals. Cattle between the age of 5 and 15 months are affected most, and deworming typically increases weight gain in these animals by 0.1 to 0.2 kg/ day. Results from deworming studies with cows and calves have been inconsistent. Parasite control in commercial livestock operations is dependent mainly on use of chemotherapy, although biological control could be effective. Grazing management variables such as stocking rate, method of grazing (rotational vs. continuous) and supplementation appear to have little effect on the need to deworm cattle. Future research should include work on improving the understanding of parasite life cycles and ecology, the inconsistency of results from deworming cows and calves, and improving experimental procedures.