Time required by different anthelmintics to reach expected efficacy levels in horses infected by strongyles.
The aim of this study was to determine the time required by different anthelmintic agents to reduce strongyle egg shedding in horses. Fifty horses were divided into five homogenous groups based on faecal egg counts (FECs). Treatment groups received either ivermectin; moxidectin; fenbendazole; piperazine; or no treatment (control group). Faecal examinations were performed 4, 8, 12, 18, 24, 36 and 48h after the anthelmintic treatment. After this period, faecal samples were taken every 24h over the next 12days and finally on alternate days (48-h intervals) for another 14days until the end of the experiment (28days post-treatment). The faecal egg count reduction (FECR) was calculated based on the post-treatment mean FECs in the controls and treated animals. Eggs were absent from the faecal examinations beginning at 72h and 4days, respectively, following treatment with moxidectin or ivermectin. Piperazine showed an FECR greater than 95% from 48h up to 9days post-treatment, with the highest FECR value recorded at 7days post-treatment (98.1%). However, the FECR was lower than 90% in the last two samplings (26 and 28days post-treatment). The febendazole group presented the lowest efficacy with FECR below 90% in all samplings. The faecal cultures showed that at the beginning of the trial, all of the groups presented with mixed infections and were predominantly composed of cyathostomins (92.8%), followed by Strongylus vulgaris (5.6%) and Triodontophorus serratus (1.6%). Only cyathostomin larvae were identified following treatment with fenbendazole or piperazine. In conclusion, horses in the present study had a segment of the cyathostomin population with resistance to fenbendazole and piperazine. The strongyle population was susceptible to macrocyclic lactones, with cessation in egg shedding three and four days after treatment with moxidectin and ivermectin, respectively.
UNESP - São Paulo State University, Dracena, SP, CEP 17900-000, Brazil. Electronic address: isa.l.s@hotmail.com.
Isabela de Lima
IL
Saes
FCAA - Andradina School of Agrarian Sciences, Andradina, SP, Brazil.
João H S
JHS
Vera
UNESP - São Paulo State University, Dracena, SP, CEP 17900-000, Brazil.
Daniele F
DF
Fachiolli
UNESP - São Paulo State University, Dracena, SP, CEP 17900-000, Brazil.
Paulo H
PH
Yamada
UNESP - São Paulo State University, Dracena, SP, CEP 17900-000, Brazil.
João V T
JVT
Dellaqua
UNESP - São Paulo State University, Dracena, SP, CEP 17900-000, Brazil.
Rafaela de Lima
RL
Saes
UNESP - São Paulo State University, Institute of Biosciences, Botucatu, SP, CEP 18618-689, Brazil.
Alessandro F T
AFT
Amarante
UNESP - São Paulo State University, Dracena, SP, CEP 17900-000, Brazil.
Ricardo V G
RVG
Soutello
D000818:Animals; D000871:Anthelmintics / Q000493:pharmacokinetics* / Q000627:therapeutic use; D005243:Feces / Q000469:parasitology; D005260:Female; D006736:Horses; D008297:Male; D010270:Parasite Egg Count / Q000662:veterinary; D013319:Strongyle Infections, Equine / Q000188:drug therapy*
D000871:Anthelmintics
Egg shedding; Equine; Fenbendazole; Ivermectin; Moxidectin; Reduction in EPG