The effect of an intranasally delivered Lactobacillus spp. cocktail on the upper and lower respiratory microbiome of dairy calves challenged with Mannheimia haemolytica

Twenty-four Holstein bull calves (1-to-3-week old) received either an intranasal BT cocktail containing six Lactobacillus strains (3 × 109 CFU per strain) 24 h or saline (control) prior to intranasal Mannheimia haemolytica challenge (3 × 108 CFU). The effect on the upper and lower respiratory microbiome was assessed using 16S rRNA gene sequencing of nasopharyngeal swabs and tracheal wash samples.