51 Evaluation of the Effects of a Single Intranasal Dose of Essential oil Spray on the Nasopharyngeal Microbiota of Feedlot Cattle: A Pilot Study

Abstract

Abstract Five essential oils (EO) were previously characterized in vitro and identified as candidates for the development of an intranasal EO spray to inhibit the colonization and proliferation of bovine respiratory disease (BRD) pathogens, especially at feedlot entry when cattle are most susceptible to BRD. In the present pilot study, these EO were evaluated for their potential to reduce BRD pathogens and to modulate nasopharyngeal microbiota in feedlot cattle. Angus-crossbred calves [n = 40; 7to 8 months old; initial BW = 284 ± 5 kg (SE)] received either an intranasal EO spray consisting of ajowan, thyme, fennel, cinnamon leaf, and citronella (0.025%, vol/vol per EO) suspended in PBS (3 mL per nostril) or PBS (Control) on day (d) 0. Deep nasopharyngeal swabs were collected on d -1 (24 h before EO administration), 1, 2, 7, 14, 28, and 42, and processed for microbiota characterization using 16S rRNA gene. The calves that received EO had similar feed intake (P = 0.62) and average daily gain (P = 0.37) than control calves. Overall bacterial concentration estimated by qPCR was greater in control (P =0.049) than EO group, with EO group having reduced bacterial concentration on d 2 (P = 0.01) and d 7 (P=0.07). Sequencing results revealed that overall community structure of nasopharyngeal microbiota was different between EO and control calves (PERMANOVA: R2 = 0.01, P = 0.02), and was strongly affected by time (R2 = 0.1, P = 0.001). Within individual sampling day, the effect of EO on community structure was only detected on d 1 (R2 = 0.05, P = 0.03). Microbial richness (observed ASVs) and diversity (Shannon and Inverse Simpson) were not different between the two groups (P ≥ 0.17). The effect of EO on the most dominant phyla was observed (P ≤ 0.05) with Proteobacteria (d14), Firmicutes (d1, 14), Actinobacteriota (d14), and Bacteroidota (d2, 14). Among the predominant genera: Moraxella, Ralstonia, Mycoplasma, Mannheimia, Filobacterium, Pseudomonas, Pasteurella, and Corynebacterium, the abundance of Mannheimia (4.34% vs. 10.4%) and Filobacterium (2.53% vs. 11.9%) were reduced (P < 0.05) by EO on d 2. In control calves, Mannheimia was enriched by 3.9-fold (P < 0.05) from d -1 (2.66%) to d 2 (10.4%), whereas it remained constant in EO calves (P > 0.05) between these days (2.23% and 4.34%). Corynebacterium was also decreased (P < 0.05) in EO calves on d 1 (1.06% vs. 2.58%). The BRD-associated Histophilus genus was low (mean 0.02%), so EO effect was not assessed. Overall, a single dose of intranasal EO spray modulated nasopharyngeal microbiota and reduced the abundance of Mannheimia within 48 h post administration while having no effect on feed intake and daily gain. Our study highlights that nasally dosing EO may modulate respiratory microbiota and potentially mitigate bovine respiratory disease in finishing cattle.