A field study on the efficacy of doramectin against strongyles and its egg reappearance period in horses.

The research paper investigates the efficiency of doramectin in treating horses infected with strongyles, as well as exploring the timeframe within which the eggs of the parasite reappear after treatment.

Study Design and Execution

• The study lasted 34 weeks and involved a group of 10 yearlings which were naturally infected with the strongyles parasites.
• They were treated with doramectin (administered via intramuscular injection) at a dose rate of 0.2 mg per kg of the horse’s bodyweight at the start of the grazing season.
• Another group of yearlings was also used for comparability, and they were treated with ivermectin (administered orally) at a similar dose rate.
• The researchers then examined individual faecal samples at two-week intervals to determine the number of strongyle eggs per gram of faeces.
• The horses received a second treatment with their respective anthelmintic 12 weeks later, followed by a third treatment whenever the mean egg count reached 200 or more.

Treatment Efficacy and Egg Reappearance Period

• The efficacy of doramectin and ivermectin was determined based on the decrease in mean egg counts two weeks post treatment. Here, the efficacy of doramectin was found to equal to or more than 96%, while that of ivermectin was 100%.
• The highest and lowest extents of efficacy for doramectin were recorded at 90% and 41%, occurring two weeks and ten weeks post-treatment respectively. In contrast, ivermectin’s effectiveness decreased from 100% (two weeks post-treatment) to 24.3% (eight weeks post treatment).
• The Egg Reappearance Period (ERP), which is the interval between treatment and the time eggs can be detected in faecal samples, was found to be 10 weeks for doramectin and 8 weeks for ivermectin. This indicates that the larvae from the hatched eggs became adults and started producing eggs after this period.

Conclusion

• The study concludes that both doramectin and ivermectin are effective in combating strongyles infections in horses, with ivermectin showing total efficacy two weeks post treatment. However, over time, the efficacy of both dewormers decreased.