Use of oxibendazole for control of cambendazole-resistant small strongyles in a band of ponies: a six-year study.

The researchers sought to explore the effectiveness of oxibendazole (OBZ) to control strongylosis in a band of ponies over a six-year period. They discovered that while the drug was initially effective, the potential for resistance grew over time, with the mean annual increase in survivorship of the strongyle infections being 10.3% over the six years.

Study Objectives and Methodology

• The research work sought to understand the efficiency of oxibendazole (OBZ) in the control of cambendazole-resistant small strongyles in a group of ponies over six years (from 1978 to 1984).
• The OBZ was administered to different numbers of Shetland-type ponies (ranging between 29 to 50) every 8 weeks.
• The effect of OBZ administration was tracked using pretreatment and posttreatment counts of the number of strongyle eggs per gram of feces (epg) and the number of strongyle larvae per gram of feces (lpg).

Initial Findings and Observations

• In the first year, the OBZ treatment showed substantial effectiveness, reducing the count of strongyle eggs by a mean rate of 96%.
• In the second and third years, the mean reduction rates were 80% and 81% respectively.

Pattern of Decreasing Effectiveness

• From the fourth to the sixth year, the effectiveness of OBZ in reducing the epg counts started diminishing significantly, with mean reduction rates standing at 69%, 43%, and 37% respectively.
• Using statistical analyses of the epg data, the study reveals a significant increase in residual (surviving) strongyle infections after the periodic OBZ treatments. This suggests a growth in resistance to the OBZ treatments over time.

Concluding Observations

• While changes in lpg were not consistent, an overall loss of effectiveness of OBZ treatments was evident.
• Only small strongyle larvae were identified in the cultures while larvae of two large strongyle species were conspicuously absent.