Livestock farming faces problems related to diseases caused by gastrointestinal nematodes such as performance decline, the risk of anthelmintic resistance or the risk of the presence of chemical substances in animal products. In our study, we evaluated the effect of the enrichment of standard compound feed with individual medicinal plants or their mixtures and the trace element selenium on the course of infection in lambs infected with Haemonchus contortus. Production indicators represented by weight gain, and the intensity of infection represented by egg production and the total number of parasites in the abomasum were monitored. The evaluation of the effect of plant extracts on different developmental stages of H. contortus in vitro was also monitored. Ovicidal activity was observed in wormwood and mallow extracts, but the addition of dried plants, despite the confirmed presence of secondary metabolites, did not significantly affect weights, egg production or the number of parasites in the abomasum in lambs. Treatment with a mixture of medicinal plants (Herbmix) and organic selenium (Selplex) did not affect body weight and weight gain. In egg production, a significant reduction was observed from day (D) 91, which at the end of the experiment on D119 represented a 53 % reduction in egg production in both treated groups. The positive effect of Herbmix and Selplex was also recorded in the number of parasites in the abomasum, where Herbmix reduced the average number of adult parasites by 36 % and Selplex by 51 % compared to the control. The antiparasitic effect of Herbmix was also confirmed by its extracts, which at a concentration of 25 mg/ml inhibited egg hatching by 83 %. No significant damage to surface structures was observed by scanning electron microscopy after exposure to Herbmix and Selplex. Supplementation with sainfoin pellets rich in tannins, flavonoids and terpenoids significantly affected weight gain in lambs. Differences in egg production at the end of the experiment showed statistical significance with a reduction of 37 %. A similar significant decrease was also recorded in the average number of adult parasites in abomasum with a reduction of 31 %. Sainfoin extracts did not damage the cuticle of adult parasites, but showed a statistically significant ovicidal effect. While the exposure time of lambs required 91 days to record the effect in Herbmix experiment, in sainfoin its effect was already observable after 14 days. In our experiments, we confirmed the antiparasitic effect of Herbmix, Selplex and sainfoin, which were able to slow down the dynamics of the infection and improve the overall health of the animals.