Field evaluation of an albendazole intraruminal capsule against benzimidazole-resistant Haemonchus contortus
Fisher, M.A.; Jacobs, D.E.; Jones, P.A.
Veterinary Record 130(16): 351-352
1992
ISSN/ISBN: 0042-4900 PMID: 1595176 Document Number: 403586
The trial was conducted in 1990 on a farm with evidence of benzimidazole (BZ)-resistant H. contortus. The flock of 300 mixed breed ewes which had been turned out in early April after lambing was divided into 3 groups and treated single doses with of albendazole (Valbazen 2.5% Total Spectrum Wormer; 5 mg/kg) orally on days 0 (April 26) and 21 followed by ivermectin on days 34 and 62 to prevent pasture contamination (Group 1), with a controlled release intraruminal capsule (Proftril-Captec; CRIC) containing 3.85 g of albendazole (providing a dose rate of 0.55 mg/kg/day for a 70 kg ewe over a period of 100 days) on day 0 (Group 2) or with oral ivermectin (Oramec) on days 0, 21 and 62 (Group 3). 15 ewes from each group were monitored using faecal egg counts, larval culture and by egg hatch assay. Results indicated that BZ resistance was restricted to H. contortus on the farm and that the strain of H. contortus was susceptible to ivermectin. The faecal egg count of the CRIC-treated ewes showed a steady fall from 31% of the initial value on day 21, to 5% by day 62 and 1% by day 90. On day 90 mean egg counts in the CRIC-treated ewes were 94.8% lower than that for Group 1 and 97.7% lower than that for Group 3. Rise in egg output of groups 1 and 3 after treatment indicated that all ewes were exposed to reinfection; this challenge was shown to include BZ-susceptible Ostertagia circumcincta and BZ-resistant H. contortus. The CRIC-treated ewes showed lower egg counts throughout much of the study which indicated prophylactic activity against both of these genera. Low yields of larvae from faecal cultures of group 2 ewes suggested that the sustained release of albendazole exerted an ovicidal effect.