Epidemiological approach to the control of horse strongyles.

The research investigates the seasonal patterns of strongyle infections in horses and assesses different treatment strategies for controlling these infections. The study shows that both strategic prophylactic treatments were more effective than conventional ones at managing infection.

Research Overview

The study was conducted on two commercial horse farms in the northern USA in 1981 and 1982. It involved an analysis of strongyle egg output during different seasons, and the observation of associated patterns of infective larvae concentration on pasture. The research also included different treatment programs to find the most successful approach for controlling strongyle infection.

Observations

• The researchers found a distinct pattern of two spring and summer rises in faecal egg counts, peaking in May and August/September.
• The concentration of infective strongyle larvae on pasture increased two to four weeks following these peaks, posing a significant risk to horses grazing from June onwards.
• Pasture larval counts remained high until the next year’s June on one of the farms.
• The number of eggs didn’t appear related to the date of foaling, suggesting the increases were driven by weather and environmental elements or the life cycle of the worms rather than the life-cycle of the horses themselves.

Treatment Strategies

• Prophylactic treatments in spring, aimed at prevention, successfully eliminated the spring rise in egg output but were insufficient to control the summer rise or the autumn increase in pasture infectivity.
• This spring prophylactic approach outperformed the conventional treatment program that used pyrantel pamoate at eight-week intervals.
• However, a modified prophylactic schedule of pyrantel pamoate at four-week intervals or ivermectin at eight-week intervals during spring and summer was found to be much more effective. These treatment schedules resulted in lower egg counts.
• As few as two treatments with ivermectin (in May and July) resulted in a sixfold decrease in pasture larval count in November and January for the treated group.

Conclusion

The study concludes that strategic treatment strategies work better than conventional treatments for strongyle control in horses, with a modified prophylactic approach showing the most promise. This research could inform treatment protocols for strongyle management in horse farms, resulting in healthier horses and better farm productivity.