Worm control practices on sheep farms in Nyandarua District of Kenya.

A questionnaire investigation was used to examine anthelmintic usage and practical worm control for sheep on 50 farms selected randomly in Nyandarua District of Central Kenya. Control of helminths was based primarily on the use of anthelmintics on all 50 farms. On the majority (54%) of these properties, lambs were drenched two times per year. Ewes and rams were drenched three or four times per year on 74% of the farms. Most treatments were given at intervals of approximately 3 months with no specific drenching programmes. Anthelmintic doses for the sheep were based on weights estimated using visual appraisal on 98 and 96% of the properties for lambs and adult sheep, respectively. Only on a small proportion of the farms (22%) was the recommended weight of the heaviest animal used when drenching groups of either lambs or adult sheep. In 1994, the majority (68%) of farmers used levamisole (LEV) in combination with oxyclosanide (OXY) a fasciolicide, 10% used benzimidazoles (BZs), 10% LEV alone and 12% LEV and BZs together. This pattern of anthelmintics use was maintained from 1988 to 1994. Eighty one percent of the farmers had been using only LEV or BZs for three or more consecutive years from 1990 to 1994. The implications of these findings for the development of anthelmintic resistance are discussed.