Characterization of the dairy cattle rumen microbial communities in response to long term supplementation of a sodium-saccharin based sweetener during normal physiological and heat stress conditions
Date
2022-08
Authors
Koester, Lucas R
Major Professor
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Schmitz-Esser, Stephan
Lyte, Mark
Looft, Torey
Phillips, Gregory J
Koltes, James E
Committee Member
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Abstract
Ruminant animals can metabolize and gain energy from plant substrates via microbial communities fostered by the host in the rumen. The rumen microbial communities are divided into three distinct classes: 1.) the feed-associated rumen content microbial communities, 2.) the planktonic microbial communities that float freely in the liquid fraction of the rumen content (together considered the rumen content microbiota (RCM)), and 3.) the microbial communities that adhere to the epithelial surface of the rumen (the rumen epithelial microbiota, REM). The RCM has been widely studied, both taxonomically and functionally, containing a high abundance of fiber and carbohydrate utilizers. A bulk of the feedstuffs, including cellulose, are metabolized in the rumen content, and it is estimated that the RCM represent >99% of the total microbial biomass in the rumen. Conversely, as they constitute <1% of the overall total microbial biomass, the REM is comparatively understudied. Previous research suggests the REM may have host-related functional roles within the rumen including 1) oxygen scavenging, 2) tissue recycling, and 3) hydrolysis of urea. In Chapter 2, we generated the first REM metagenome shotgun sequencing dataset from Holstein-Friesian milking dairy cattle, elucidating the genetic potential of this niche microbial community. We identified genes belonging to several important pathways including: nitrogen cycling, sulfur cycling, oxidative stress response, and propionic acid and butyric acid synthesis, assimilatory sulfate reduction, synthesis of essential amino acids, and genes related to denitrification and nitrogen fixation.
Additionally, we tested the effect of Sucram® (Pancosma S.A./ADM Groups, Rolle, Switzerland), a sodium-saccharin-based sweetener, on RCM and REM under normal physiological conditions and during heat stress conditions. In Chapters 3 and 4, 16S rRNA gene amplicon sequencing was conducted on both RCM and REM in Holstein-Friesian milking dairy cattle supplemented with Sucram®, with Chapter 4 including a heat stress component. It was discovered that after supplementation of Sucram® under normal physiological conditions, significant changes in the abundance of specific taxa were detected: an increase in Prevotella and Sharpea species, a decrease in Treponema, Leptospiraceae, Ruminococcus and methanogenic archaea, but Sucram® did not affect the overall rumen microbial community structure. The effect was larger under heat stress conditions, demonstrating supplementation of Sucram® during heat stress did not affect the RCM, but significant changes in REM community composition and community structure were detected. Despite the changes in microbial community, acetic, butyric and propionic acid concentrations were unchanged by supplementation of Sucram®. Additionally, Chapter 4 revealed that Sucram® supplementation during heat stress did not alter animal performance measures such as feed intake or milk yield either.
Finally, it was discovered that the rumen microbial communities in adult cows remain stable over long period of time, when diet was held constant. A majority of studies monitoring fluctuations in rumen microbial communities take place over shorter periods of time (1 or 2 weeks), and aim to test the effect of dietary manipulation. Very few studies focus on temporal aspects of rumen microbial communities, and none of these studies have included analysis of the REM. In the study presented in Chapter 2, samples of the RCM and REM of five lactating Holstein-Friesian dairy cattle were collected at equal intervals (30 days) across three months, and analyzed using 16S rRNA gene sequencing. It was found that these communities remain stable in community composition and species diversity, being indistinct across sampling time points in both RCM and REM. Additionally, all of the genes of interest within the REM metagenomic dataset were present at each time point, suggesting these functions are stable as well.
The sequencing data generated in each study will be publically available to assist future research and strengthen new hypothesis. Importantly, the work herein greatly expands upon our knowledge of the REM, and has presented new hypothesis about their contributions to host health and performance. This work also offers new insight into the effects of HS and Sucram® on rumen microbial communities, demonstrating both stimuli impact the RCM and REM individually, and uniquely when combined. Altogether, these data provide researchers with a deeper understanding of the taxonomy and function of rumen microbial communities.
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dissertation