SURVEY ON THE ANTHELMINTIC EFFICACY OF BENZIMIDAZOLES AGAINST GASTROINTESTINAL STRONGYLIDS OF SHEEP IN SOUTHEASTERN BULGARIA

The efficacy of benzimidazole anthelmintics was investigated in 15 randomly selected sheep farms located in southeastern part of Bulgaria. The in vitro egg hatch assay (EHA) was performed after anaerobical storage of mixed faecal samples from each farm for 2 – 5 days. Pure thiabendazole was used in solutions of 0.02; 0.04; 0.05; 0.08 and 0.1 µg.ml –1 . Effective dose (ED50) was calculated. On each farm, 30 sheep were allocated at random into two groups of 15 animals each: an untreated control group and a group that was orally administrated albendazole (Valbazen ® , Pfizer Animal Health) (3.8 mg.kg –1 ) or oxfendazole (Oxfenil ® , Virbac Animal Health) (5.0 mg.kg –1 ). Individual faecal egg counts were estimated before and 14 days after treatment and faecal egg count reduction (FECR) was calculated, for performing the in vivo egg faecal count reduction test (FECRT). Mixed farm faecal samples were cultivated for 7 days at 27 o C for developing and identification of strongylid larvae III. The predominant genus was Haemonchus. In all the examined sheep farms the ED50 of thiabendazole was below 0.1. All the flocks showed FECR values over 95%. No developed anthelmintic resistance was detected. From the results of the present trial can be concluded that benzimidasoles are high effective against sheep gastrointestinal strongylids in southeastern Bulgaria.