AUTHOR=Gao Qian , He Jianfu , Wang Jin , Yan Yonghui , Liu Lei , Wang Zuo , Shen Weijun , Wan Fachun 

TITLE=Effects of dietary D-lactate levels on rumen fermentation, microflora and metabolomics of beef cattle

JOURNAL=Frontiers in Microbiology

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2024.1348729

DOI=10.3389/fmicb.2024.1348729

ISSN=1664-302X

ABSTRACT=<sec><title>Introduction</title><p>Excessive intake of lactate caused by improper use of silage in animal husbandry has adverse effects on rumen fermentation, such as rumen acidosis. The speed of absorption and metabolism of <italic>D</italic>-lactate in rumen epithelial cells was slower than that of <italic>L</italic>-lactate, making <italic>D</italic>-lactate more prone to accumulate and induce rumen acidosis. Therefore, this study was conducted to explore the effects of dietary <italic>D</italic>-lactate levels on rumen fermentation of beef cattle and its mechanism in an <italic>in vitro</italic> system.</p></sec><sec><title>Methods</title><p>This experiment was adopted in single-factor random trial design, with 5 days for adaptation and 3 days for sample collection. Three treatments (<italic>n</italic> = 8/treatment) were used: (1) D-LA (0.3%), basal fermentation substrate with 0.3% (dry matter, DM basis) <italic>D</italic>-lactate; (2) D-LA (0.75%), basal fermentation substrate with 0.75% (DM basis) <italic>D</italic>-lactate; and (3) D-LA (1.2%), basal fermentation substrate with 1.2% (DM basis) <italic>D</italic>-lactate.</p></sec><sec><title>Results</title><p>With the dietary <italic>D</italic>-lactate levels increased, the daily production of total gas, hydrogen and methane, as well as the ruminal concentrations of acetate, propionate, butyrate, isobutyrate, valerate, isovalerate, total volatile fatty acid and <italic>D</italic>-lactate increased (<italic>p</italic> &lt; 0.05), but the ruminal pH and acetate/propionate ratios decreased (<italic>p</italic> &lt; 0.05). Principle coordinate analysis based on Bray-Curtis distance showed that increasing dietary <italic>D</italic>-lactate levels could significantly affect the structure of rumen bacterial community (<italic>p</italic> &lt; 0.05), but had no significant effect on the structure of rumen eukaryotic community (<italic>p</italic> &gt; 0.05). <italic>NK4A214_group</italic>, <italic>Ruminococcus_gauvreauii_group</italic>, <italic>Eubacterium_oxidoreducens_group</italic>, <italic>Escherichia-Shigella</italic>, <italic>Marvinbryantia</italic> and <italic>Entodinium</italic> were enriched in D-LA (1.2%) group (<italic>p</italic> &lt; 0.05), as well as <italic>WCHB1-41</italic>, <italic>vadinBE97</italic>, <italic>Clostridium_sensu_stricto_1</italic>, <italic>Anaeroplasma</italic> and <italic>Ruminococcus</italic> were enriched in D-LA (0.3%) group (<italic>p</italic> &lt; 0.05). Changes in the composition of ruminal microorganisms affected rumen metabolism, mainly focus on the biosynthesis of glycosaminoglycans (<italic>p</italic> &lt; 0.05).</p></sec><sec><title>Discussion</title><p>Overall, feeding whole-plant corn silage with high <italic>D</italic>-lactate content could not induce rumen acidosis, and the metabolization of dietary <italic>D</italic>-lactate into volatile fatty acids increased the energy supply of beef cattle. However, it also increased the ruminal CH<sub>4</sub> emissions and the relative abundance of opportunistic pathogen <italic>Escherichia-Shigella</italic> in beef cattle. The relative abundance of <italic>Verrucomicrobiota</italic> and <italic>Escherichia-Shigella</italic> may be influenced by glycosaminoglycans, reflecting the interaction between rumen microorganisms and metabolites.</p></sec>