The relationship between the rumen microbiome and carcass merit in Angus steers

Authors: KRAUSE, TAYLOR - University Of Georgia; LOURENCO, JEFFERSON - University Of Georgia; WELCH, CHRISTINA - University Of Georgia; Rothrock, Michael; CALLAWAY, TODD - University Of Georgia; PRINGLE, DEAN - University Of Georgia

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/31/2020
Publication Date: 9/2/2020
Citation: Krause, T.R., Lourenco, J.M., Welch, C.B., Rothrock Jr, M.J., Callaway, T.R., Pringle, D.T. 2020. The relationship between the rumen microbiome and carcass merit in Angus steers. Journal of Animal Science. 98(9):1-12.

Interpretive Summary: Profitability in the beef industry is heavily influenced by the quality and quantity of end products. Therefore, opportunities to improve both the quality and yield grades of beef carcasses at the producer level should be fully explored. The ruminal microbial ecosystem has a significant impact on overall host metabolism and nutrient availability, and alterations in the microbial populations in the rumen could impact energy partitioning and subsequent carcass composition. The objective of this study was to explore the relationships between microbial populations in the rumen of Angus steers that were divergent in carcass merit traits related to adipose accumulation. Twenty Angus steers were slaughtered, and ruminal contents and carcass data were collected. Microbial DNA extraction and 16S rRNA gene sequencing were performed to estimate microbial diversity and to predict microbial metabolic pathways. A variety of correlations and one-way ANOVA were performed to investigate the relationships between the rumen microbiome and carcass traits. Marbling score and longissimus lipid content were both positively correlated (P=0.004) to Chao1 richness index, suggesting that increased intramuscular fat content was associated with increased numbers of ruminal microbial species. The phylum Cyanobacteria was negatively correlated to marbling score (P=0.001) and longissimus lipid content (P=0.003), indicating that lower abundances of Cyanobacteria were linked to increased marbling scores and greater lipid content. Greater abundances of the bacterial family S24-7 was positively correlated (P=0.002) to marbling scores. Analysis by marbling classification revealed further differences in microbial richness (P=0.016), diversity (P=0.016), and S24-7 (P=0.001). Several phyla, families, and genera were positively correlated (P=0.014) to both backfat thickness and yield grade. Analysis using Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) to predict microbial metabolic pathways revealed no differences (P=0.05) in metabolic function between high- and low-marbling classes. Collectively, our results imply that differences in microbial abundances are linked to differing performance in carcass adipose traits. Overall, bacterial taxa correlating to the 2 fat depots, intramuscular and subcutaneous, did not overlap; thus, suggesting the microbial population impacts adipose accumulation in various depots via separate pathways of the host animal.

Technical Abstract: Profitability in the beef industry is heavily influenced by the quality and quantity of end products. Therefore, opportunities to improve both the quality and yield grades of beef carcasses at the producer level should be fully explored. The ruminal microbial ecosystem has a significant impact on overall host metabolism and nutrient availability, and alterations in the microbial populations in the rumen could impact energy partitioning and subsequent carcass composition. The objective of this study was to explore the relationships between microbial populations in the rumen of Angus steers that were divergent in carcass merit traits related to adipose accumulation. Twenty Angus steers were slaughtered, and ruminal contents and carcass data were collected. Microbial DNA extraction and 16S rRNA gene sequencing were performed to estimate microbial diversity and to predict microbial metabolic pathways. A variety of correlations and one-way ANOVA were performed to investigate the relationships between the rumen microbiome and carcass traits. Marbling score and longissimus lipid content were both positively correlated (P=0.004) to Chao1 richness index, suggesting that increased intramuscular fat content was associated with increased numbers of ruminal microbial species. The phylum Cyanobacteria was negatively correlated to marbling score (P=0.001) and longissimus lipid content (P=0.003), indicating that lower abundances of Cyanobacteria were linked to increased marbling scores and greater lipid content. Greater abundances of the bacterial family S24-7 was positively correlated (P=0.002) to marbling scores. Analysis by marbling classification revealed further differences in microbial richness (P=0.016), diversity (P=0.016), and S24-7 (P=0.001). Several phyla, families, and genera were positively correlated (P=0.014) to both backfat thickness and yield grade. Analysis using Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) to predict microbial metabolic pathways revealed no differences (P=0.05) in metabolic function between high- and low-marbling classes. Collectively, our results imply that differences in microbial abundances are linked to differing performance in carcass adipose traits. Overall, bacterial taxa correlating to the 2 fat depots, intramuscular and subcutaneous, did not overlap; thus, suggesting the microbial population impacts adipose accumulation in various depots via separate pathways of the host animal.