Overberg Research Projects: III. A preventive worm control programme for sheep in the Rûens, in the winter rainfall region of South Africa.

The mass gains and internal parasite burdens of a flock of untreated ewes and lambs were compared with those of a similar flock of treated ewes and lambs. These data, combined with climatic data, were used to compile a nematode parasite control programme for sheep in the Rûens, a sub-region of the winter rainfall area of South Africa. Teladorsagia were the most numerous parasites in the ewes and later in the season, also in the lambs. From July onwards, the development of Teladorsagia was inhibited regardless of previous exposure to worms, the number of worms present or the age of the host. Initially, Nematodirus dominated in the lambs and its development was not inhibited. Low numbers of Nematodirus, mainly inhibited, were found in the ewes. Both parasites were rife in winter but disappeared from the pasture during spring, while Trichostronglus rugatus, the dominant species of Trichostronglus, infested the lambs in spring and persisted in them throughout summer. Anthelmintic treatments had no significant effect on the live mass gains of ewes and suckling lambs while they were on lush, but heavily infested lucerne pastures for 5.5 months, but after a further 6 months on safe wheat stubble pastures, the overall mean live mass gain of the treated lambs was a significant 4.7 kg more than that of the untreated lambs. The integrated, preventive worm control programme recommended consists of pre-winter, pre-spring and pre-summer treatments with broad spectrum anthelmintics, but transfer to safe pastures after each treatment is essential.