We addressed whether gut microbiome development affected the developing immune response in neonatal calves. Twenty-eight Holstein cows and their female calves were included in this study. The calves received 3 to 6.5 L of fresh colostrum within 18 h of birth. Next, all calves were fed 6 L of milk replacer per day and calf starter ad libitum. Calf health was assessed immediately after birth and at 3, 7, 14, 21 and 28 d of age. Gut health was evaluated by fecal score and samples were harvested for laboratory analysis. The total DNA of all fecal samples were extracted using PowerSoil DNA Isolation kit. The V3-V4 region of 16S rDNA was amplified and sequenced by the Illumina MiSeq high-throughput sequencing platform. Sequences were analyzed using Qiime. The fraction of calves with diarrhea increased between 1 and 10 of age (peaking at 40%). Indicators of innate immunity demonstrated a decrease in the number of neutrophil and basophil on d 7 with a decrease in production of reactive oxygen species. It may be that granulocytes migrated to the gut at this time. Evidence of adaptative immunity indicated an initial decrease in ex vivo lymphocyte proliferation on d 7 then a gradual increase as the calves aged. The cytokines produced by ex vivo lymphocyte stimulation with bacteria or mitogen were minimal at d 3 but gradually increased for IL-17 and IFN-gamma as the calves aged. The early resident bacteria were predominantly Staphylococcus, Escherichia coli, and Clostridia spp. during the first 7 d. Subsequently, an increase in the number of Fecalibacterium and Bacteroides were observed over the rest of the study. Feces from healthy calves (fecal score 0) had an abundance of Bifidobacterium and Lactobacillus. In contrast, fecal samples from calves with diarrhea showed an abundance of Fusobacteria phylum. In conclusion, calves showed stronger innate responses early in life concurrent with initial bacterial colonization. As they aged, the adaptative immune elements showed signs of enhanced activity that may be associated with the establishment the bacterial community in the gut.
Key Words: innate immune response, adaptative immune response, diarrhea, Faecalibacterium, Bacteroides.
Presented at the 9th Symposium on Gut Health in Production of Food Animals, St. Louis, USA, 2021. For information on the next edition, click here.