Ivermectin still highly effective against strongyles in horses in Poland, study shows

No strongyle resistance to the common worming drug ivermectin was detected in a study of 173 horses bred in Poland.

Agnieszka Żak and her colleagues, writing in the journal BMC Veterinary Research, noted that there were no available studies describing the possible resistance of strongyles to ivermectin in horses in Poland.

The horses used in the study were from nine stud farms from south-western Poland. All were routinely dewormed twice a year by the stud-farm operators.

All horses underwent a fecal egg count at the start of the study to assess their worm burdens before being given a dose of ivermectin paste by mouth by a veterinarian. The dose was based on body weight, which was measured with a girth tape.

The effectiveness of the drug was studied on the 14th day after it was given using a fecal egg count reduction test. The testing revealed that the ivermectin had been highly effective in killing the strongyles.

In the second part of the study, the egg reappearance period was assessed in 42 of the horses from two stables, selected based on an eggs-per-gram value of more than 20.

Fecal samples from these horses were collected and tested weekly until their worm burden reached 10% of that recorded before the study began.

The egg reappearance period ranged from seven to 16 weeks from the time the ivermectin was given, indicating that it was not shortened.

They found no evidence of strongyle ivermectin-resistance in the horses, based on the tests conducted.

“The results,” they concluded, “indicate that strongyle resistance to ivermectin in Poland is not a serious problem.

“Despite these results, it is necessary to undertake measures that will limit future strongyle resistance, such as the use of correct deworming methods and selective deworming.

“Currently,” they noted, “great emphasis is placed on deworming procedures in Poland.

“Veterinary professionals and horse owners are encouraged to use selective deworming schemes in order to limit future ivermectin resistance.”

The researchers are variously affiliated with the Wroclaw University of Environmental and Life Sciences, and the University of Wroclaw.

Searching for ivermectin resistance in a Strongylidae population of horses stabled in Poland
A. Zak, N. Siwinska, M. Slowikowska, H. Borowicz, K. Kubiak, J. Hildebrand, M. Popiolek and A. Niedzwiedz
BMC Veterinary Research 2017 13:210 DOI: 10.1186/s12917-017-1133-1

The study, published under a Creative Commons License, can be read here

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