Bovine mastitis is an inflammation of the udder, usually caused by bacterial infection. The disease is complex, difficult to cure and costs the worldwide dairy industry an estimated $35 billion (US) annually in production losses. Good herd management and animal husbandry can reduce the incidence of mastitis, however treatment with antibiotics is generally required to facilitate cure. Therapeutic treatment of these infections is with intramammary infusion of antibiotics however cure rates are often low. Additionally treatment has been associated with the development of antibiotic resistance. Dairy industries in many countries are looking to reduce the use of antibiotics therefore effective alternative or complementary chemotherapies need to be investigated for routine treatment of bovine mastitis.

 Many plant essential oils are known to be antimicrobial. We are currently studying a selection of oils for their antibacterial activities, including interactions between oils and interactions between oils and commonly used antibiotics. We have tested a range of oils against the mastitis causing bacteria Escherichia coli, Staphylococcus aureus, Streptococcus agalactiae, Streptococcus dysgalactiae and Streptococcus uberis using both disc diffusion and broth assays in standard and milk containing media.

 Several oils have been identified with good bactericidal activity. These include basil, cinnamon leaf, oregano and thyme oils. While these oils have broad spectrum activity, there are differences in response of the organisms to individual oils. Due to the hydrophobic nature of essential oils it was reasoned that the lipid content of milk may facilitate the suspension of oils in milk therefore improving their efficacy. It was found, however, that bactericidal effects were reduced in milk compared to aqueous media.