# Molecular Identification and Benzimidazole Resistance Analysis of Cyathostomins in Chinese Grazing Horses

## TL;DR

This study analyzed cyathostomin parasites in Chinese grazing horses, finding high infection rates but no resistance to albendazole, a key deworming drug.

## Contribution

The study provides the first detailed baseline data on cyathostomin species and anthelmintic resistance in Chinese horses.

## Key findings

- 88.9% of horses were moderate-to-high egg shedders, indicating high parasite pressure.
- Cylicocyclus nassatus and Cylicostephanus spp. were the dominant species identified.
- No benzimidazole resistance or β-tubulin isotype-1 mutations were detected in the studied population.

## Abstract

Cyathostomins are the most prevalent intestinal parasites of horses, commonly associated with ill-thrift and reduced performance. This study assessed parasite burdens and species composition in 90 adult grazing horses in China. Fecal egg counts revealed that 88.9% of horses were moderate-to-high egg shedders, indicating substantial environmental parasite pressure. Species identification showed dominance of Cylicocyclus nassatus and Cylicostephanus spp., consistent with global patterns. All identified cyathostomins remained susceptible to albendazole, and the β-tubulin isotype-1 mutation associated with benzimidazole resistance was not detected. These findings provide important baseline information on cyathostomin infections and anthelmintic resistance in horses from China where such data have been limited, and they may help guide future parasite control strategies.

This study investigated the cyathostomin species composition, anthelmintic efficacy, and potential resistance-associated mutations in Chinese grazing horses. Fecal samples were collected from 90 adult horses. Fecal egg counts (FECs) were determined using a modified McMaster method. Third stage larvae (L3) cultured from the eggs were identified to species level by PCR amplification and sequencing of the internal transcribed spacer-2 (ITS-2). The main species included Cylicocyclus nassatus and Cylicostephanus spp. However, differences in the relative abundance of less common species, including Cyathostomum pateratum and Cylicocyclus ashworthi, suggests regional variation. Anthelmintic efficacy was assessed by a fecal egg count reduction test (FECRT) following albendazole administration. Mutations at six codons of the β-tubulin iso-type-1 (tbb-iso-1) gene were screened by gene sequencing. The results showed that, despite harboring an abundant and diverse cyathostomin community, this herd remained susceptible to albendazole. Overall, this study provides baseline data on cyathostomin species composition and anthelmintic susceptibility in horses from China, contributing to global surveillance of equine cyathostomin resistance.