A Field Evaluation of Pro-Benzimidazole, Benzimidazole, and Non-Benzimidazole Anthelmintics in Horses

Abstract

SUMMARY The effectiveness of 1 pro-benzimidazole (pro- bzd ) drug, 3 benzimidazole ( bzd ) drugs, and 3 non-benzimidazole (non- bzd ) drugs in keeping fecal egg counts below 50 eggs per gram 2 and 4 weeks after treatment at 6-week intervals was compared in groups of brood mares and yearlings at 2 Standardbred farms. In a preliminary study (December 1978 to April 1979) as well as a major study (April to November 1979), horses were kept in the same groups in the same areas. In the major study, treatments were arranged in a Latin square design. On farm 1, which had a history of repeated use of bzd drugs since 1964, the non- bzd drugs, dichlorvos and pyrantel pamoate, rated 83%-100% in their ability to suppress egg counts below 50 eggs per gram. They were significantly better ( P <0.05) than pro- bzd (febantel) or bzd (cambendazole, fenbendazole, mebendazole) drugs, which rated 13%-58%. Phenothiazine-piperazine-carbon disulfide rated 60%-77% on farm 1 and also was significantly better ( P <0.05) than pro- bzd or bzd drugs. On farm 2, which had a history of limited use of bzd drugs, there was no significant difference between the 3 classes of anthelmintics, which all rated between 67% and 100%. Results of larval culture showed small strongyles to be the major source of high egg counts. In all groups of horses, irrespective of the treatment, there was a marked increase in fecal egg counts by 6 weeks after treatment.