Evaluation of generic injectable ivermectin for control of nematodiasis in feedlot heifers

Abstract

Nematode parasitism of feedlot cattle has received very little research attention. It is assumed that anthelmintics administered at feedlot entry are effective and that feedlot conditions preclude post-treatment infection by helminths. Given the paucity of information about feedlot nematodiasis, the current research project was conducted. During October of 2010, 104 animals were selected at random from approximately 1600 beef heifers received at one feedlot in California and penned as a group. Of those, 96 were administered a generic, injectable formulation of ivermectin at label dose, while the remaining eight animals were left as untreated controls. Controls and eight randomly selected treated animals were necropsied for parasite quantifications at eight weeks post-treatment. At the end of the feeding period (approximately 135 days post-treatment), parasite quantifications were performed on nine animals selected at random from the remaining 88 animals. Fecal samples were periodically collected from cattle in the feedlot during the study. As evidenced by reductions in both fecal egg count and parasite quantifications at necropsy, a lack of drug efficacy was apparent for Cooperia and Ostertagia, and suspect for Haemonchus infections.