Pre-established anthelmintic protocols in horses: low efficacy and unnecessary treatments highlight the need for strategic deworming
Rafaella Back Neves A , Denise Pereira Leme
A * , Fernando Jahn Bessa B , Giuliano P. de Barros B and Patrizia Ana Bricarello A
+ Author Affiliations
- Author Affiliations
A Departamento de Zootecnia e Desenvolvimento Rural, Universidade Federal de Santa Catarina, Florianópolis, 88040-900, SC, Brazil.
B Programa de Pós-Graduação em Agroecossitemas, Universidade Federal de Santa Catarina, Florianópolis, 88040-900, SC, Brazil.
Animal Production Science 63(12) 1226-1235 https://doi.org/10.1071/AN22223
Submitted: 12 June 2022 Accepted: 27 April 2023 Published: 26 May 2023
© 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing
Abstract
Context: Deworming all horses with commercial anthelmintics on a rotational basis every 90 days is still popular worldwide.
Aims: To investigate anthelmintic resistance and therapeutic requirements of adult horses on the basis of faecal examinations after a rotation between commercial anthelmintics commonly used in Brazil.
Methods: We followed up faecal egg counts and coprocultures of 29 horses for 7 months, after pre-established anthelmintic treatments, every 3 months (August and November 2019 and February 2020). The following commercial anthelmintics were used respectively: moxidectin (1), ivermectin + praziquantel (2) and trichlorfon + mebendazole (3). Faecal egg count (FEC), FEC reduction tests (FECRT) and coproculture were performed before (Day 0) and after 14 days for each of the three treatments. Wilcoxon test (95% confidence level, P < 0.05) was used to test the efficacy of the treatment on the FECRT and the occurrence of resistance to the treatments used.
Results: The FEC results and percentage of individual FECRT indicated parasite resistance, and 82 of 87 (94%) deworming treatments were unnecessary. The efficacy rate was 78%, 34% and 53% for Treatments 1, 2 and 3 respectively. In the coprocultures before deworming, 98.5% were small strongyles, 1.1% Strongylus equinus and 0.4% Gyalocephalus capitatus. After deworming, 98.7% of parasites were small strongyles and 1.3% Dictyocaulus arnfieldi. FEC values at Day 0 and 14 days after anthelminthics were different (lower) only for the moxidectin treatment (U = 271.5; P-value <0.01). For both ivermectin + praziquantel (U = 373; P-value >0.05) and mebendazole + trichlorfon (U = 391; P-value >0.05) treatments, there was no difference in FEC between Day 0 and Day 14 at 95% confidence level.
Conclusions: The anthelmintics used in the deworming protocol of this study had reduced efficacy against the parasites identified in the coprocultures and the pre-established treatments were probably unnecessary in 93% of the horses with a low level of infection.
Implications: This study has highlighted not only the issue of the indiscriminate use of anthelmintics regarding parasitic resistance, but also the exposure of horses to unnecessary treatments. Such widespread use is a costly waste of resources and further reinforces the discontinuation of schedule rather than strategic deworming protocols.
Keywords: anthelmintic resistance, cyathostomins, deworming, equine, faecal egg counts, helminthic control, parasites, strongyles.
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