A combined trial of chemotherapy and biological control measures against parasites in grazing horses

Abstract

Horses under grazing regime are at a high risk for infection by several parasites affecting the digestive tube, especially the strongyles. Infection occurs by the ingestion of free-living third stage larvae (also called L3) when grazing in pastures. While deworming reduces the presence of adult parasites in the horses, some action against the L3 in the pasture is needed for reducing the risk of infection. Eight adult horses exceeding a cut-off value of 300 eggs per gram of feces (EPG) were utilized in the current study. Control of parasitic strongyles consisted of the combination of two measures. Firstly, the horses were given moxidectin (Equest® oral gel, Pfizer, Madrid, Spain; 0.4 mg/kg bw dosage), and in addition, a dose of 2×10 6 Duddingtonia flagrans chlamydospores kg/bw was bi-weekly given to each horse. The effect of this combined procedure was assessed by estimating the reduction in the faecal egg counts. After the horses received the chemotherapy and the D. flagrans chlamydospores a significant reduction in the EPG was observed (Z=-11.391, P= 0.001). No strongyle egg-output was observed for 2 months, whereas the need for applying a new dosage of chemotherapy was established at the 6 th month after the initial deworming of the equines. Our results point the efficacy of a combined strategy by giving chemotherapy and chlamydospores for reducing the frequency of antiparasitic drug administration to grazing horses. Besides the presence of free-infective larval stages can be significantly lowered and thus the risk of infection in the horses, this procedure seems a very valuable and helpful contribution to the sustainability of the environment by minimizing the effect of chemical residues dangerous for some organisms as dung beetles, essential for the natural fertilization of the soil.