Prevalence and control of benzimidazole-resistant small strongyles on German thoroughbred studs.

This study investigates how common benzimidazole-resistant small strongyles are on German thoroughbred studs, and compares the effectiveness of different treatments in reducing these parasites’ egg counts both immediately and six weeks post-treatment.

Research Background and Methodology

• Small strongyles, also known as cyathostomes, are a type of gastrointestinal parasites often found in horses, which can develop resistance against commonly used de-worming drugs like benzimidazoles.
• The study was based in Germany and involved 14 thoroughbred studs, where small strongyles prevalence was tested.
• The researchers compared faecal egg counts of groups of horses before and after they were treated with two kinds of benzimidazoles – cambendazole (20mg per kg body weight) and febantel (6mg per kg body weight).

Findings: Benzimidazole Resistance

• The research found that on every stud farm examined, the small strongyles were resistant to benzimidazole, the commonly used drug for their treatment, demonstrating an alarming rate of resistance across the board.

Investigation of Other Treatments

• Given the resistance to benzimidazoles, the researchers then tested three other drugs: pyrantel pamoate (19mg per kg body weight), oxibendazole (10mg per kg body weight) and ivermectin (0.2mg per kg body weight).
• Two weeks post-treatment, all three drugs had reduced the strongyle egg counts on these studs by between 97% to 100%, showing that they were effective in the short term.

Six Weeks Post-Treatment Findings

• However, the situation was different 6 weeks after treatment. Pyrantel pamoate and oxibendazole had reduced strongyle egg output to an average of only 67.8% and 51.2% respectively, suggesting that the effectiveness of these drugs decrease over time.
• In contrast, ivermectin continued to suppress egg counts by an average of 98.2%, remaining highly effective even six weeks after treatment.

Significance of the Findings

• The research shows a high prevalence of benzimidazole-resistant small strongyles on German thoroughbred studs, hinting at the need for alternate forms of treatment.
• The study suggests that while pyrantel pamoate and oxibendazole can be effective in the short term, their effectiveness seems to diminish over time.
• On the other hand, ivermectin remained highly effective even six weeks post-treatment, making it a potentially more reliable choice for treating benzimidazole-resistant small strongyles.