An introductory survey of helminth control practices in South Africa and anthelmintic resistance on Thoroughbred stud farms in the Western Cape Province

Fifty-one per cent of 110 questionnaires, designed for obtaining information on helminth control practices and management on Thoroughbred stud farms in South Africa, were completed by farmers during 2000. The number of horses per farm included in the questionnaire survey ranged from 15 to 410. Foals, yearlings and adult horses were treated with anthelmintics at a mean of 7.3+ / -3.0, 6.6+ / -2.7 and 5.3+ / -2.3 times per year, respectively. An average of 3.4 different drugs were used annually, with ivermectin being used by most farmers during 1997-2000. On 43% of farms the weights of horses were estimated by weigh band and 45% of farmers estimated visually, while both were used on 7% of farms and scales on the remaining 5%. Doses were based on average group weight on 50% of the farms and on individual weights on 46%. Forty-three per cent of farmers performed faecal egg count reduction tests (FECRT). Most farmers rotated horses between pastures and treated new horses at introduction. Faecal removal was practiced on 61% of farms and less than 50% of farmers used alternate grazing with ruminants. Faecal egg count reduction tests were done on 283 horses, using oxibendazole, ivermectin and moxidectin on 10, 9 and 5 farms, respectively, in the Western Cape Province during 2001. While the efficacy of oxibendazole was estimated by FECRT to range from 0-88% and moxidectin from 99-100%, ivermectin resulted in a 100% reduction in egg counts. Only cyathostome larvae were recovered from post-treatment faecal cultures.