COMPARATIVE CURATIVE AND PREVENTIVE EFFICACIES OF IVERMECTIN AND CLOSANTEL ON ESTRUS-OVIS (LINNE-1758) IN NATURALLY INFECTED SHEEP

A field trial was undertaken to assess the efficacy of each of two for mulations of ivermectin and of closantel in prevention and treatment o f Oestrus ovis in a naturally infected flock grazing on the foothills of the Pyrenees mountains, in south-western France. Within the flock, 875 sheep were randomly divided into four groups, and treated twice du ring the fly season, with an interval of 60 days between treatments. G roup 1 sheep were treated with albendazole (ABZ) at a dose rate of 3.8 mg/kg to maintain control of trichostrongylid parasites without affec ting O. ovis; Group 2 received closantel at a dose rate of 10 mg/kg be cause of its known persistent activity against O. Ovis; Groups 3 and 4 received ivermectin at a dose rate of 200 mcg/kg bodyweight by subcut aneous injection (Isc) and orally (Io), respectively. All sheep were m anaged as a single group throughout the study. In order to assess the prophylactic effect of each product, immediately prior to the schedule d second treatment on Day 60 (D60), five sheep from each group were ch osen at random and necropsied. Similarly, to assess the therapeutic ef fect another five sheep from each group were selected on D70 and necro psied for parasite counts. During the 120 days of the trial, a signifi cant number of animals from each group were regularly individually exa mined to assess their clinical status with regard to O. Ovis infection . Clinical signs of infection had significantly declined in Groups 2, 3 and 4 by 10 days after treatment reaching their lowest level at D30. In the control group during this period, clinical signs increased. Te n days after the second treatment, (D70), there was also evidence of a significant response to treatment, Finally the between-treatment diff erences in clinical scores of the closantel and ivermectin groups were small, although scores in Group 1 sheep was suggestive of a higher ch allenge in the second half of the study. On the basis of the postmorte m counts and arithmetic means, prophylactic efficacies for the treatme nts relative to ABZ treated group, were 97.7, 62.5 and 0%, for the clo santel, isc and Io groups respectively. Therapeutic efficacies for the closantel, Ise and Io were 100, 100 and 98% respectively. (C) 1997 El sevier Science B.V.