Assessing the impact of Salmonella infection on the gastrointestinal microbiota of dairy calves.
A total of 10 Holstein x Angus cross calves from a single farm were enrolled at birth into this study between September 2022 and April 2023. Calves were housed in individual pens in an isolated room with no nose-to-nose contact and screened for Salmonella presence through three weeks of age. During the fourth week of age all calves were orally infected with 1mL of Salmonella enterica serotype Typhimurium (strain ST4/74) inoculum at a dose of 2 x 107 - 8 x 107 CFU/mL. Calf health was monitored for three days following infection and euthanized on day 3 to assess progression across the gastrointestinal tract. Fecal samples were collected daily starting the day before infection through euthanasia. Intestinal contents from the ileum, cecum, spiral colon, and descending colon were collected at sacrifice. From each of these samples, the V4 region of the 16S rRNA gene was sequenced on an Illumina MiSeq using a 2 x 250, 500-cycle, v2 sequencing kit. These sequences were used to investigate how the fecal microbiota are impacted during a virulent Salmonella infection and if there is variability in microbiota composition across the gastrointestinal tract.