Viljoen, J.H.Weiss, K.E.2016-07-062016-07-0620161969Viljoen, JH 1969, 'Further studies on the epizootiology of nematode parasites of sheep in the Karoo’, The Onderstepoort Journal of Veterinary Research, vol. 36, no. 2, pp. 233-263.0330-2465http://hdl.handle.net/2263/53863The articles have been scanned in colour with a HP Scanjet 5590; 300dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.The dominant parasites in the Karoo are Nematodirus spathiger (Railliet, 1896) and Trichostrongylus falculatus Ransom , 1911 . In the moister eastern regions Haemonchus contortus (Rudolphi, 1803) and Oesophagostomum columbianum (Curtice, 1890) occur but they decrease markedly as the region becomes more arid. Ostertagia circumcincta (Stadelmann , 1894) is of little or no significance. The free-living stages of N. spathiger are highly resistant to heat and desiccation, but T. falculatus cannot survive if the mean monthly mean temperatures exceed 20°C and even if the monthly rainfall exceeds 50 mm, there is but a slight increase in worm burdens. Both species reach peak worm burdens in winter. The presence of H. contortus or possibly 0. columbianum has a deleterious effect on N. spathiger. Strategic drenching is recommended in March and July and tactical drenching when climatic conditions are favourable.en© 1969 ARC - Onderstepoort and Faculty of Veterinary Science. University of Pretoria (original). © 2016 University of Pretoria. Department of Library Services (Digital).Veterinary medicineVeterinary medicine -- South AfricaArticle