Overberg research projects. XVI. First-stage larval reduction test versus the controlled anthelmintic test to assess the efficacy of anthelmintics against nematode parasites of sheep.

Results of a first-stage larval reduction test (L1RT) were compared with those of a controlled anthelmintic test (CAT) done on naturally infected sheep which grazed on spray-irrigated grass/legume pastures at Tygerhoek Experimental Farm near Riviersonderend in the southern Cape Province. The 3 anthelmintics used were morantel, ivermectin and levamisole. According to the L1RT, treatments reduced the geometric means of Strongyloides by 74.2 to 95.2% and those of the adults of all the other genera (Haemonchus, Nematodirus, Oesophagostomum, Teladorsagia, Trichostrongylus and Trichuris) by 99.4 to 99.75%. By contrast the results of the CAT were more variable, placing the reliability of the L1RT in doubt. In addition, the CAT could also evaluate the effect against fourth larval stage Teladorsagia.