Does the upper respiratory tract microbiome change in dairy calves fed milk replacer containing probiotics?

Abstract

Our overall hypothesis is that feeding probiotics to dairy calves will alter overall immunity and may additionally change the microbiome in the respiratory tract as well as the gut. A group of 20 dairy calves were split into two treatment groups: Control (N=10, milk replacer), and Probiotic (N=10, milk replacer + 0.5 g/day Bovamine Dairy). On day 0 birth weight was obtained and the calves were provided colostrum as per the dairy SOP. On day 2, probiotics were added to the milk replacer of the treated group. Blood was collected along with nasal and tonsil swabs on days 0, 7, 14, 21, 28, 42, and 48. Calves were monitored daily for fecal, nasal, and ocular discharge scores. Our preliminary data showed no significant differences (P<0.5) between the Control and Probiotic groups in immune cell populations in peripheral blood. DNA was extracted from nasal and tonsil swabs to evaluate the bacterial populations in the upper respiratory microbiome. Hypervariable regions 1 through 3 along the 16S ribosomal RNA gene were amplified by PCR and sequenced by Illumina MiSeq to determine the bacterial taxa present. Evaluation of these samples revealed a greater percentage of operational taxonomy units (OTU) were classified at the genus level in the tonsil compared to the nasal samples. The microbiome of the tonsils was more stable over time points compared to the nasal samples. Evaluation of each timepoint for nasal and tonsil samples identified bacterial taxa that changed in relative abundance with the addition of the probiotic compared to the control diet. Addition of probiotic changed the relative abundance of OTU (P<0.01) in the nasal and tonsil sampling sites and at multiple timepoints. Analyses are ongoing. Project supported by fund from the USDA Agricultural Research Service.