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The extensive use of antibiotics has contributed to the current antibiotic resistance crisis. Livestock infections of <i>Salmonella</i> spp, <i>Clostridium</i> spp. and <i>E. coli</i> antimicrobial-resistant bacteria represent a public threat to human and animal health. To reduce the incidence of these zoonoses, essential oils (EOs) could be effective antibiotic alternatives. This study aims at identifying EOs safe for use, effective both in complementary therapy and in the environmental sanitization of intensive farming. Natural products were chemo-characterized by gas chromatography. Three <i>S.</i> Typhimurium, three <i>C. perfringens</i> and four <i>E. coli</i> strains isolated from poultry and swine farms were used to assess the antimicrobial properties of nine EOs and a modified GR-OLI (mGR-OLI). The toxicity of the most effective ones (<i>Cinnamomum zeylanicum</i>, Cz; <i>Origanum vulgare</i>, Ov) was also evaluated on porcine spermatozoa and <i>Galleria mellonella</i> larvae. Cz, Ov and mGR-OLI showed the strongest antimicrobial activity; their volatile components were also able to significantly inhibit the growth of tested strains. <i>In vitro</i>, Ov toxicity was slightly lower than Cz, while it showed no toxicity on <i>G. mellonella</i> larvae. In conclusion, the study confirms the importance of evaluating natural products to consolidate the idea of safe EO applications in reducing and preventing intensive livestock infections.