A field evaluation of pro-benzimidazole, benzimidazole, and non-benzimidazole anthelmintics in horses.

The research examines the efficacy of three categories of anthelmintic drugs on two horse farms. The results showed variance based on prior usage history of these drugs and all horse groups showed a rise in fecal egg counts six weeks post-treatment.

Research Context

• This study was conducted to assess the effectiveness of various anthelmintic drugs which are used for the treatment of parasitic worm infestations in horses.
• These drugs included one pro-benzimidazole (pro-BZD), three benzimidazole (BZD), and three non-benzimidazole (non-BZD) drugs.
• The researchers measured success by the ability of these drugs to keep fecal egg counts below 50 eggs per gram two and four weeks after treatment. This was repeated at six-week intervals.

Research Methodology

• The study was carried out on groups of brood mares and yearlings at two Standardbred horse farms. In both a preliminary and major study, horses were kept in the exact same groups in their usual living areas.
• Treatments in the major study were assigned following a Latin square design, a method used in experiments to reduce the influence of confounding factors.

Results on different farms

• On Farm 1, which previously used BZD drugs since 1964, the non-BZD drugs (dichlorvos and pyrantel pamoate) were able to suppress egg counts below 50 eggs per gram with an effectiveness of 83%-100%. This made them significantly better than the pro-BZD (febantel) or BZD (cambendazole, fenbendazole, mebendazole) drugs, which had an effectiveness rating of just 13%-58%.
• Meanwhile, on Farm 2, which had only limited prior use of BZD drugs, there were no significant differences amongst the three classes of anthelmintics, all of which had an effectiveness rating between 67%-100%.

Other Key Findings

• Larval culture results indicated that small strongyles were the major source of high egg counts in the feces.
• Regardless of the treatment received, all groups of horses displayed a significant spike in fecal egg counts six weeks after the treatment was administered, suggesting a limitation to the long term effectiveness of the treatment strategies.