Abstract
<title>Abstract</title> <p> Effective control of <italic>Haemonchus contortus</italic> showing anthelmintic resistance remains a major challenge in sheep production systems. Plant-based treatments may represent a sustainable alternative for parasite control. This study evaluated the <italic>in vitro</italic> and <italic>in vivo</italic> anthelmintic effects of the leaves of <italic>Caryocar brasiliense</italic> , an important tree species from the Cerrado biome. High-performance liquid chromatography analyses detected tannins and flavonoids in the aqueous (AE) and ethanolic (EE) extracts. In the egg hatching inhibition test, the LC <sub>90</sub> values of AE and EE were 15.88 and 9.48 mg/mL, respectively. However, both extract showed increased efficacy after tannin extraction. The maximum tolerated dose in both male and female mice was 100 mg/kg body weight. No clinical signs of toxicity, mucosal tissue alterations, changes in animal behavior, or mortality were observed during the four days of extract administration. In the larval development inhibition assay, the LC <sub>90</sub> values for the dried powder and AE were 64.80 and 38.55 mg/g of fecal culture, respectively. The inclusion of <italic>C. brasiliense</italic> leaves in the diet showed high <italic>in vivo</italic> efficacy in reducing fecal egg counts in lambs infected with the nematode, while blood parameters remained within the physiological reference ranges for sheep. These results highlight the potential of <italic>C. brasiliense</italic> , a Cerrado plant species, as an alternative strategy for the control of <italic>H contortus</italic> in sheep. </p>