Efficacy of fenbendazole-medicated feed blocks against gastrointestinal nematode infections in calves.

An anthelmintic trial was conducted to determine the efficacy of fenbendazole (FBZ) incorporated into two types of feed blocks given daily for 3 or 10 days to calves naturally parasitized with gastrointestinal nematodes. Each treated calf consumed 5 mg of FBZ/kg of body weight. The FBZ was greater than 99% effective in removing adults of Haemonchus contortus, Ostertagia ostertagi, O lyrata, Cooperia punctata, C pectinata, C onchophora, Trichostrongylus axei, Bunostomum phlebotomum, and Oesophagostomum radiatum. Fenbendazole was also greater than 99% effective against immature nematodes recovered from the small intestine, which were thought to be mainly Cooperia spp. Efficacy was similar for FBZ in each of the two types of feed block carriers and for the 3- and 10-day regimens. Calves readily consumed feed blocks containing FBZ and did not have adverse reactions to FBZ.