Differences in the microbial community abundances of dairy cattle divergent for milk urea nitrogen and their potential implications

Authors: MARSHALL, CAMERON - Lincoln University - New Zealand; GARRETT, KONAGH - Lincoln University - New Zealand; Beck, Matthew; BARRELL, GRAHAM - Lincoln University - New Zealand; AL-MARASHDEH, OMAR - Lincoln University - New Zealand; GREGORINI, PABLO - Lincoln University - New Zealand

Submitted to: Applied Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2021
Publication Date: 1/28/2022
Citation: Marshall, C.J., Garrett, K., Beck, M.R., Barrell, G.K., Al-Marashdeh, O., Gregorini, P. 2022. Differences in the microbial community abundances of dairy cattle divergent for milk urea nitrogen and their potential implications. Applied Animal Science. 38:62-69. https://doi.org/10.15232/aas.2021-02220.
DOI: https://doi.org/10.15232/aas.2021-02220

Interpretive Summary: A considerable amount of protein consumed by ruminants is not used for production but is excreted into the environment through urine and feces. Nitrogen excretion, especially from urine, represents a significant environmental concern due to nitrate leaching and greenhouse gas emissions. Milk urea nitrogen concentration is a strong indicator of urine nitrogen in dairy cows. Previous research by scientists from Lincoln University (Lincoln, New Zealand) and ARS (Bushland, Texas) have reported the potential for a milk urea nitrogen breeding value to identify cows which have reduced urine nitrogen excretions. Low milk urea nitrogen breeding value cows consistently have lower urine nitrogen excretions and our research efforts have demonstrated that these cows also exhibit differences in grazing behavior. However, potential ruminal microbiome differences in divergent milk urea nitrogen breeding value dairy cows have not been explored. As such, researchers from ARS (Bushland, Texas) and Lincoln University analyzed ruminal fluid for bacterial community composition. Low milk urea nitrogen dairy cows had lower concentrations of a bacteria called Succinivibrio and greater concentrations of anther bacteria called Kandleria. These differences in microbial community composition may provide a possible physiological explanation behind the milk urea nitrogen breeding value, which warrants further investigation.

Technical Abstract: Objective: The first objective of this experiment was to determine and describe any differences in rumen microbiome relative abundances between dairy cattle divergent for milk urea nitrogen breeding values (MUNBV). The second objective was to ascertain whether any difference in rumen microbiome relative abundances may be associated with phenotypical differences already observed in dairy cattle divergent for MUNBV. Materials and Methods: Rumen microbiome data were collected and collated from multiple trials that had been conducted investigating differences in dairy cattle divergent for MUNBV where samples rumen samples were taken via esophageal tubation. Results and Discussion: On average 8% of the rumen microbiome genera detected differed in their relative abundance based on MUNBV. High MUNBV dairy cattle had a 10% increase in the relative abundance of Basfia and a 20% increase in the relative abundance of Succinivibrio compared to low MUNBV dairy cattle. Both Basfia and Succinivibrio have potential implications for rumen fermentation that requires further investigation. High MUNBV dairy cattle also had a 17% increase in the relative abundance of Kandleria compared to low MUNBV dairy cattle. Higher relative abundances of Kandleria may be affecting the health status of dairy cattle classified as high MUNBV resulting in higher incidences of increase somatic cell counts. Implications and Applications: Knowledge of differences in the relative abundance of the rumen microbiome of dairy cows divergent for MUNBV highlights areas where future research is required as well as the potential for using MUNBV as a metric for increasing animal welfare.