Effects of Intranasal Prebiotics, Probiotics and Synbiotics on the Nasopharyngeal Microbiota of Feedlot Cattle

Abstract The emergence of antibiotic-resistant pathogens associated with bovine respiratory disease (BRD) presents a significant challenge to the beef industry, as antibiotic administration is commonly used to prevent and control BRD in feedlot cattle. Alternatives to antibiotics are therefore needed as part of new management strategies to reduce antibiotic use and BRD. We recently developed probiotics comprised of six Lactobacillus strains that inhibited the BRD pathogen Mannheimia haemolytica, and conferred longitudinal modulation of the nasopharyngeal microbiota in calves when a single dose was administered intranasally. In the present study, we evaluated the effects of a prebiotic (lactulose) alone and in combination with probiotic bacteria on the nasopharyngeal microbiota of feedlot calves. The probiotic bacteria consisted of 6 strains of Lactobacillus originated from the nasopharyngeal microbiota of healthy feedlot cattle. The calves were assigned to one of five treatments (n = 8 calves per treatment) and house individually: 1) Syringe-Probiotic group received intra-nasal probiotic cocktail via syringe that was attached to a 25-cm long catheter; 2) MAD-Probiotic group received an intra-nasal probiotic cocktail with a mucosal atomization device; 3) MAD-Synbiotic group received an intra-nasal probiotic cocktail containing prebiotic lactulose (0.5%, suspended in PBS) with a mucosal atomization device; 4) MAD-Prebiotic group received intra-nasal prebiotic lactulose (0.5%, suspended in PBS) with a mucosal atomization device; and 5) MAD-PBS (Control) group received only PBS with a mucosal atomization device. Utilization of a syringe versus mucosal atomization device was tested to determine if mode of probiotic bacteria delivery had an impact on the respiratory microbiota. Deep nasopharyngeal swab samples were collected on day 0 (24 h prior to treatment administration), 2 (24h post intranasal treatment), 3, 6, 9 and 14 days. Genomic DNA was extracted from the swabs and processed for nasopharyngeal microbiota characterization by sequencing 16S rRNA gene amplicon sequencing. When administered to calves intranasally, lactulose had no effect on the diversity or community structure of bacteria (PERMANOVA, P > 0.05) and had limited prolonged effect on specific genera. In addition, when administered as a synbiotic with a multi-strain cocktail of Lactobacillus probiotic bacteria, colonization was not enhanced. However, probiotic bacteria did affect the bacterial structure of NP bacteria (P < 0.05) and increased microbial network interactions. The strongest effect was observed when probiotic bacteria were administered alone, using an atomization device. Overall, this study showed that the bovine respiratory microbiota can be altered by administration of probiotics and may therefore provide new opportunities to enhance microbiome-mediated respiratory resistance against BRD pathogens. While colonization and growth of probiotic bacteria in the respiratory tract are unlikely to be modified by prebiotics delivered in PBS solution, the delivery method and time of application are important factors that need to be evaluated to have optimal efficacy of biologicals.