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The development of resistance to commercial anthelmintics, particularly in different species of gastrointestinal nematodes (GINs), requires the search for alternatives. Within that context, the aim of this study was to evaluate the in vitro ovicidal activity of five different essential oils (EOs): Origanum vulgare, Satureja hortensis, Thymus vulgaris, Mentha x piperita and Helichrysum arenarium against sheep GINs. For this purpose, the nematode eggs were collected from naturally infected sheep by GINs in two farms located in southern Italy. The egg hatch test (EHT) was performed at six different concentrations (50, 12.5, 3.125, 0.781, 0.195 and 0.049 mg/mL) for each EO. Gas chromatography-mass spectrometry chemical analyses of tested EOs, as well as coproculture examination of tested faecal samples, were also conducted. The results of EHT showed the greatest ovicidal activity of O. vulgare EO with a maximum effect on egg hatching (100%) for all tested concentrations. A similar effect was also shown by S. hortensis and T. vulgaris EOs with an activity of 99.3-100% and 98.5-100%, respectively. M. piperita EO showed medium, dose-dependent ovicidal activity with an inhibitory effect of 72.5-99.8% on the egg hatchability, while the least effective was H. arenarium EO with an activity of 59.8-69.3%. For the anthelmintic activities of the tested EOs are responsible their ingredients, above all carvacrol, thymol, p-cymene and γ-terpinene. The present study demonstrated the significant anthelmintic potential of the tested EOs and emphasizes the possible importance of medicinal plant products for the control of gastrointestinal parasites in sheep.

Herbal products such as essential oils may play a promising role in the treatment of infections caused by gastrointestinal nematodes (GINs). The aim of this study was to evaluate the in vitro potential of 11 essential oils (EOs) and one binary combination of isolated EO compounds, as well as the in vivo anthelmintic efficacy of two EO formulations. Four GIN genera were identified in the coproculture examination: Haemonchus, Trichostrongylus, Teladorsagia and Chabertia. The in vitro egg hatch test (EHT) was performed at six different concentrations (50, 12.5, 3.125, 0.781, 0.195 and 0.049 mg/mL) for each EO, whereas in the in vivo faecal egg count reduction test (FECRT), each EO sample was diluted in sunflower oil and orally administrated at a dose of 100 mg/kg to the different group of animals. In the EHT, the EOs of Origanum vulgare, Foeniculum vulgare, Satureja montana, Satureja hortensis and two types of Thymus vulgaris were the most effective. The dominant compounds of these EOs were carvacrol, thymol, anethol, p-cymene and γ-terpinene, indicating their importance for the anthelmintic activity. In the FECRT, both T. vulgaris EO type 1 and linalool:estragole combination show an anthelmintic potential with a mean effect on FECR of approximately 25%. The results suggest the possible role of tested EOs as anthelmintic agents in sheep farms, although further in vivo tests are needed. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.