Effects of lavender essential oil nebulisation on welfare and nasal microbiota of growing-fattening pigs

Three experimental groups of 36 pigs each (average weight 79 kg) were kept for 127 days in the following experimental conditions: standard farming (C = control), lavender oil nebulisation for 10 min once a day (L1) or lavender oil nebulisation twice a day (L2). No significant differences were observed across groups in growth parameters and chronic stress levels (hair cortisol, dehydroepiandrosterone and their ratio). Behavioural analysis showed similar activity levels across groups, but significant differences for some behaviours: L1 explored the pen floor less than C (p < .05); stood inactive more than L2 (p < .05) and spent the largest proportion of time eating (p < .01). Pigs from group L2 were more frequently observed in a sitting inactive position than C (p < .05) and showed a lower interaction with pen-mates and a greater interaction with objects than L1 and C (p < .05 and p < .01, respectively). A positive effect due to a moderate reduction in aimless exploration of the barren floor could be identified in L1 compared with C (p < .05), but the difference did not reach statistical significance in L2. Regarding nasal microbiome, beta diversity was not affected by treatment, while L2 pigs showed tendentially increased alpha diversity compared to C (Chao1 and Shannon indexes, p = .05), likely due to changes in rare taxa. Overall, these results suggest that a single or double daily administration may be insufficient to exert a robust positive effect on growth parameters, behavioural traits, stress levels or antimicrobial effect on the pig nasal microbiota, therefore different protocols and/or routes of administration should be assessed.