Background: The growing emergence of anthelmintic-resistant parasitic isolates is leading us to reconsider the management of digestive strongylosis in horses. In addition, European regulations are moving towards a reduction in the use of chemical treatments, in line with societal demand for environmentally-friendly management and the use of ”natural” alternatives. Objectives: In this context, we investigated the effect of plant-based feed additives commercialized to support the natural defenses against intestinal parasites and the immune defenses of the equines. Study design: Randomized blinded in vivo experiments Methods: Has higher concentrations than the manufacturer recommendation, three treatments based either on mugwort ( Artemisia vulgaris), echinacea ( Echinacea purpurea) or curcumin ( Curcuma longa), were administrated to 18 (six per treatment) Welsh female ponies naturally infected with cyathostomins. Six more no treated ponies were used as control group. Fecal egg count (FEC), eggs development into infective larvae, red blood cells and immune system parameters (lymphocytes, monocytes, neutrophils, eosinophils and basophils) were measured the first and the last day of each treatment, and compared with those characterizing the control group. Results: None of the three treatments showed a significant effect, on the studied parameters. However, Cohen’s size effect indicates a strong effect for all three treatments on FEC, only mugwort on larval development and on different blood cells (0.9 ≥ d ≥ 1.09). Nevertheless, the efficacy of treatments, measured from the FEC reduction (FECR) compared to the control group was weak (≤ 38.6). Main limitations: The size of the animal groups used in the study, similar to the number of horses owned by the owners, was too small to observe a significant effect. Conclusions: Under our conditions, these results provide an initial view of the antiparasitic and immunostimulant activity of three plant-based food additives. However, the measured efficacy was insufficient to justify the practical use of these additives.