##### Westion Section American Society of Animal Science Annual Meeting: Boise, Idaho

## Metagenomic analysis of rumen populations in week-old calves as altered by maternal late gestational nutrition and mode of delivery

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Thomas A. Christensen II
Kathy J. Austin
Kristi M. Cammack
Hannah C. Cunningham-Hollinger

#### June 12, 2019

Early colonization of the rumen microbiome is critical to host health and long term performance. Factors that influence early colonization include maternal factors such as gestational nutrition and mode of delivery. Therefore, we hypothesized that late gestational nutrition and mode of delivery would influence the calf rumen microbiome. Our objectives were to determine if nutrient restriction during late gestation alters the calf rumen microbiome and determine if ruminal microbiome composition differs in calves born vaginally versus caesarean. Late gestating Angus cows were randomly allocated to one of three treatment groups: control (CON; n = 6), caesarean section (CS; n = 4), and nutrient restricted (NR; n = 5), where CON were fed DDGS and hay to meet NRC requirements and calved naturally; CS were fed similarly to CON and calves were born via caesarean section; and NR were fed at a level to reduce BCS by 1.5-2.0 points over the last trimester compared to CON and calved naturally. Rumen fluid was collected via oral lavage prior to partition from cows and at d 7 from calves. Microbial DNA was isolated from the rumen fluid and metagenomic shotgun sequencing was performed using the Illumina HiSeq 2500 platform. Sequence data were analyzed using Metaxa2 for taxonomic assignment followed by QIIME1 and QIIME2 to determine differential abundance and alpha- and beta-diversity differences. There were no significant differences in alpha-diversity as measured by shannon index across treatment groups for cows (P = 0.239), but there were significant differences for calves (P = 0.015). Similarly, there were no significant differences in beta-diversity as measured by the bray-curtis dissimilarity matrix for cows (P = 0.059), but there were significant differences for calves (P = 0.007). Alpha-diversity differed (P < 0.001) between cows and calves, with cows having increased species richness compared to calves. Beta-diversity also differed (P = 0.001) between cows and calves. At total of 410 taxa were differentially abundant (P < 0.01) between cows and calves. These results suggest that the mature rumen microbiome of cows is able to withstand changes in feed intake, however the calf microbiome is susceptible to alteration by maternal factors. These data also suggest that there may be opportunities to develop management strategies during late gestation that influence calf health and performance long-term.

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