TDK conference 2020

The most prevalent parasitosis of adult horses today is strongylidosis, which is caused by small and rarely by large strongyles. Horses demonstrate huge differences in their levels of strongyle egg shedding, however, many times when horses are treated with anthelmintics, this is not taken into account, which contributes to develop resistance against drugs. The aim of this study was, on one hand, to find correlation between certain risk factors (eg. age, stocking density, history of deworming) and the number of eggs found in feces. On the other hand, we investigated whether ivermectin resistance developed.

Fecal samples and the most important data (eg. age, management, deworming) were collected from 216 horses, at 13 farms in Pest county, Hungary during spring of 2020. Fecal egg counts were performed with the use of Mini-FLOTAC technique, to determine the number of eggs per gram of feces (EPG). This was followed by peroral treatments with products containing ivermectin, in the prescribed dose on all farms. Finally, from fecal samples, collected 14 days post treatment, the EPG values were determined. Our calculations were carried out with the stats module of the scipy (1.4.1) library. EPG values amongst the various groups of horses were compared with Mann-Whitney U test.

In the present study, 132 out of 216 horses, (63,4%; 95% CI:54,5-67,4) were strongyle egg count positive. In 36,5% (95% CI: 30,4-43,2) of the samples the EPG value was higher than 200. 80% of all strongyle eggs were found in 22% (48/216) of the samples. Mean EPG values of fecal samples of horses aged 5 years or younger (907.5 EPG ±1060.53; n=35), were 3 times higher than those of horses aged above 5 years (278.85 EPG ±513.3; n=181). EPG values of horses with extreme high stocking density (>30 horses/ha; n=79) were significantly higher than those with low (1-2 horses/ha; n=16; p=0.14*10-5) or medium (3-10 horses/ha; n=73; p=0,00003) stocking density. Ivermectin treatments were 100% efficacious on all the examined farms.

To prevent resistance against anthelmintics, the number of treatments needs to be determined based on individual egg shedding, which is among others, affected by age and the number of horses kept in a certain area. Even one treatment per year can be sufficient for adult horses shedding low numbers of eggs (≤200 EPG). Although the efficacy of products containing ivermectin was proven, in case of frequent use, measuring its efficacy is important in the future too.