Effects of olfactory exposure to twelve Essential Oils (EOs) on behavior and health of cows with subclinical mastitis

International audience ; Essential oils (EO) are known for their anti-bacterial, anti-inflammatory and relaxing properties. They are used nowadays by a large number of farmers and considered as promising compounds against mastitis. We have recently found that applying Thymus capitatus EO on the mammary gland of dairy cows through massage didn’t have any effects on subclinical mastitis (SM). The aim of this study was to evaluate the effects of a scent of 12 EO belonging to different chemical families on cow’s EO preference and the follow up of SM in dairy cows. 29 Holstein cows were involved in this experiment among them 19 with signs of SM. After 2 days adaptation, animals had free access (2 days) to 12 EO distributed randomely in a fencedpilot. We combined both video recording and biological sampling to study 1) animal behaviour and preferences towards each of the 12 EO and 2) follow the evolution of SM. Blood cortisol concentrations were also evaluated to estimate the stress level after EO’s exposure. Nasal microbiota was studied from the nasal mucosa samples.For each of the healthy and SM cows, we did not observe any significant preference towards a particular EO during the whole experimentation. However, SM cows were signifiantly more attracted to monoterpene (MN) and monoterpenol (ML) EO’s families compared to healthy ones (p<0.05). Interestingly, EO with predominant ketones family were exclusively scented by the healthy cows (P<0.05). For health evaluation, no statistical differences on SCC and bacteriological status in milk were highlighted at day 21 days after EO's exposure, but we did observe a significant increase in the cortisol rate in blood compared to healthy ones.Our findings suggest that SM cows attraction to MN and ML families did not alleviate the signs of SM at day 21. Additional evaluation of the specific effects of MN and ML families on SM is needed to test different doses and other experimental conditions before any wide recommendation to farmers.