This study was carried out to evaluate the anthelmintic activity of a herbal formulation (HF) based on aqueous extracts of leaves of Azadirachta indica and Nicotiana tabacum, flowers of Calotropis procera and seeds of Trachyspermum ammi. In vitro, eggs and adult Haemonchus contortus were exposed to different concentrations of HF following the standard procedures of egg hatch test (EHT; 50 to 0.024414 mg ml^-1) and adult motility assay (AMA; 200-0.1953125mg ml^-1), respectively. The reference drugs used in the study were oxfendazole (0.0056704 to 0.0000027 mg ml^-1) and levamisole (1.50 mg ml^-1) for EHT and AMA, respectively. In vivo, pre and post-treatment (4 mg, 2 mg and 500 µg kg^-1 body weight) fecal egg counts were determined following standard fecal egg count reduction test in sheep naturally parasitized with mixed species of gastrointestinal nematodes. In EHT, LC₅₀ values of HF and oxfendazole (reference drug) were 275.1 and 0.016 µg ml^-1, respectively. In AMA, 100% mortality of H. contortus was observed 6 hr post-exposure to 3.125-200 mg ml^-1 concentrations of HF and 2 hr post-exposure to levamisole. In vivo, maximum (96.2%) fecal egg count (EPG) reduction was recorded in sheep treated with HF @ 4 mg kg^-1 body weight; whereas, 89.3% reduction in EPG was recorded in sheep treated with levamisole @ 7.5 mg kg^-1 body weight. A graded dose response was noted in all the tests used in the present study to evaluate the anthelmintic activity of HF. Therefore, HF seems to be promising as an anthelmintic for animals. Large scale trials on efficacy and safety, however, are recommended before the HF is considered for commercialization in crude form.

Key words: Anthelmintic, Gastrointestinal nematodes Herbal extracts, Sheep