Probiotics in milk replacer affect the microbiome of the lung in neonatal dairy calves

Authors: McDaneld, Tara; Eicher, Susan; Dickey, Aaron; KRITCHEVSKY, JANICE - Purdue University; BRYAN, KEITH - Chr Hansen Inc; Chitko-Mckown, Carol

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2023
Publication Date: 1/5/2024
Citation: McDaneld, T.G., Eicher, S.D., Dickey, A.M., Kritchevsky, J.E., Bryan, K.A., Chitko-McKown, C.G. 2024. Probiotics in milk replacer affect the microbiome of the lung in neonatal dairy calves. Frontiers in Microbiology. 14. Article 1298570. https://doi.org/10.3389/fmicb.2023.1298570.
DOI: https://doi.org/10.3389/fmicb.2023.1298570

Interpretive Summary: Probiotics have been investigated for many health benefits, however little research has been done to determine the effects of oral probiotics on the bacterial populations of the bovine respiratory tract. Our hypothesis for this study was that probiotic treatment would result in changes in the lung bacterial populations as measured in lung lavage fluid. A group of 20 dairy calves were split into two treatment groups: Control (CNT; N=10, milk replacer), and oral probiotic treatment (TRT; N=10, probiotic). On day 0 birth weight was obtained and the calves were provided colostrum. On day 2, probiotics were added to the milk replacer of the treated group then included in their dry ration. Lung lavages were performed on day 52 on five calves from each treatment group. Overall, evaluation of these samples revealed that the bacterial populations identified in the lungs of probiotic-fed calves as compared to the control calves are significantly different (P<0.05). Additionally, when comparing diversity of the bacterial populations in the lung lavage samples to nasal and tonsil samples, bacterial population diversity of lung samples was significantly lower (P<0.05). In conclusion, analysis of the respiratory pathogens in the lung after probiotic treatment will provide insight into the distribution of bacterial populations in response to oral probiotics.

Technical Abstract: Introduction: Probiotics have been investigated for their many health benefits and impact on the microbiota of the gut. Recent data have also supported a lung-gut axis regarding the bacterial populations (microbiomes) of the two locations; however little research has been done to determine the effects of oral probiotics on the microbiome of the bovine respiratory tract. We hypothesized for this study was that probiotic treatment would result in changes in the lung microbiome as measured in lung lavage fluid. Our overall goal was to characterize bacterial populations in the lungs of calves fed probiotics in the milk replacer and dry rations from birth to weaning. Methods: A group of 20 dairy calves was split into two treatment groups: Probiotic (TRT; N = 10, milk replacer + 5 g/d probiotics; Bovamine Dairy, Chr. Hansen, Inc., Milwaukee, WI) and Control (CON; N = 10, milk replacer only). On d 0 birth weight was obtained and the calves were provided colostrum as per the dairy SOP. On d 2, probiotics were added to the milk replacer of the treated group and then included in their dry ration. Lung lavages were performed on d 52 on five random calves selected from each treatment group. DNA was extracted from lavage fluid and 16S ribosomal RNA (rRNA) gene hypervariable regions 1 through 3 were amplified by PCR and sequenced using next-generation sequencing (Illumina MiSeq) for identification of the bacterial taxa present. Taxa were classified into both operational taxonomic units (OTUs) and amplicon sequence variants (ASVs). Results: Overall, evaluation of these samples revealed that the bacterial genera identified in the lung lavage samples of probiotic-fed calves as compared to the control calves were significantly different based on the OTU dataset (P < 0.05) and approached significance for the ASV dataset (P < 0.06). Additionally, when comparing diversity of taxa in the lung lavage samples to nasal and tonsil samples, taxa diversity of lung samples was significantly lower (P < 0.05). Discussion: In conclusion, analysis of the respiratory microbiome in the lung lavage samples after probiotic treatment provide insight into the distribution of bacterial populations in response to oral probiotics and demonstrates that oral probiotics affect more than the gut microbiome.