Evaluation of risk factors affecting strongylid egg shedding on Hungarian horse farms

In Hungary, equine parasite control is mostly based on traditional approaches involving rotational anthelmintic treatment at regular intervals. Almost no farms utilize fecal egg counts (FECs) on a regular basis to guide deworming treatments. This approach is certainly not sustainable and is the major factor responsible for the current high levels of anthelmintic resistance. The aims of this study were to statistically analyze risk factors associated with strongylid egg count magnitude and prevalence. Fecal samples and horse data (age, pasture history, stocking density, anthelmintic history) were collected from 216 horses on 13 farms in Pest county, Hungary, during the spring of 2020. FECs were determined by Mini-FLOTAC. Logistic regression models were used to evaluate the association of factors with pre-deworming strongylid egg counts. The data were highly overdispersed with approximately 22% (95% Confidence Interval: 17-28%) of the equids shedding 80% of the total strongylid egg output. Strongylid FECs were significantly associated with the age of equids and anthelmintic class used prior to the study. Equids younger than 5 years of age had significantly higher FECs compared to equids in the 5-17-year age range (p = 0.003) and compared to equids aged >17 years (p < 0.001). Equids treated regularly with benzimidazoles had significantly higher FECs than equids with no history of benzimidazole use (p = 0.02). We found that FECs of horses kept at extremely high stocking density (>30 horses/ha) were significantly higher than those kept at low (1-2 horses/ha; p < 0.001) or medium (3-10 horses/ha, p < 0.001) stocking densities. The results demonstrate the value of FEC monitoring and indicate that the efficacy of benzimidazoles should be investigated in Hungary. Moreover our findings demonstrate that reducing stocking density should be considered in cases of high strongylid FECs.