Mineral salt bricks are often used in cow raising as compensation for mineral losses to improve milk yield, growth, and metabolic activity. Generally, effects of minerals are partially thought to result from improvement of microbial metabolism, but their influence on the rumen microbiota has rarely been documented to date. In this study, we investigated the response of microbiota to mineral salt in heifer and adult cows and evaluated ruminal fermentation and enteric methane emissions of cows fed mineral salts. Twelve lactating Holstein cows and twelve heifers fed a total mixed ration (TMR) diet were randomly allocated into two groups, respectively: a treatment group comprising half of the adults and heifers that were fed mineral salt and a control group containing the other half fed a diet with no mineral salt supplement. Enteric methane emissions were reduced by 9.6% (P < 0.05) in adults ingesting a mineral salt diet, while concentrations of ruminal ammonia, butyrate, and propionate were increased to a significant extent (P < 0.05). Enteric methane emissions were also reduced in heifers ingesting a mineral salt diet, but not to a significant extent (P > 0.05). Moreover, the concentrations of ammonia and volatile fatty acids (VFAs) were not significantly altered in heifers (P > 0.05). Based on these results, we performed high-throughput sequencing to explore the bacterial and archaeal communities of the rumen samples. Succiniclasticum and Prevotella, two propionate-producing bacteria, were predominant in samples of both adults and heifers. At the phylotype level, mineral salt intake led to a significant shift from Succiniclasticum to Prevotella and Prevotellaceae populations in adults. In contrast, reduced abundance of Succiniclasticum and Prevotella phylotypes was observed, with no marked shift in propionate-producing bacteria in heifers. Methanogenic archaea were not significantly abundant between groups, either in adult cows or heifers. The shift of Succiniclasticum to Prevotella and Prevotellaceae in adults suggests a response of microbiota to mineral salt that contributes to higher propionate production, which competes for hydrogen utilized by methanogens. Our data collectively indicate that a mineral salt diet can alter interactions of bacterial taxa that result in enteric methane reduction, and this effect is also influenced in an age-dependent manner.

The delivery and utilization of O 2 is of great importance to the survival of many organisms. In eukaryotic organisms, O 2 oxidizes glucose to carbon dioxide and water, and generates adenosine 5′-triphosphate (ATP), which is essential for their survival and activities. 1 However, in some situations such as high-altitude and deep ocean habitats, subterranean tunnels, and outer space, oxygen is limited. These hypoxic environments could limit physiological functional capacity, reproductive health and even survival, 2 for example when superoxide anions are generated when electrons escape from the respiratory chain and combine with O 2 , or when organisms suffer from hypoxia, which can lead to damage in the brain, 3 lung, 4 retina, 5 liver, 6 and kidney. 7 Hypoxia occurs in a variety of situations including at high altitude, deep in the ocean, in subterranean tunnels, and in concentrated populations, or when breathing mixtures of contaminated gases. Such conditions cause various diseases or even death of the organism. In order to cope with such stresses, organisms have evolved strategies such as unique circulatory, respiratory and hematological adaptations, including single nucleotide variations (SNV), copy number variations (CNV), transposable elements, differentiated gene expression, isoforms and methylations. Many genes, 8 regulators and mutations have been identified as candidates for hypoxia adaptation using whole genome data.

The gut microbiome is important for host nutrient metabolism and ecological adaptation. However, how the gut microbiome is affected by host phylogeny, ecology and diet during sympatric speciation remain unclear. Here, we compare and contrast the gut microbiome of two sympatric blind mole rat species and correlate them with their corresponding host phylogeny, ecology soil metagenomes, and diet to determine how these factors may influence their gut microbiome. Our results indicate that within the host microbiome there is no significant difference in community composition, but the functions between the two sympatric species populations vary significantly. No significant correlations were found between the gut microbiome differentiation and their corresponding ecological soil metagenomes and host phylogeny. Functional enrichment analysis suggests that the host diets may account for the functional divergence of the gut microbiome. Our results will help us understand how the gut microbiome changes with corresponding ecological dietary factors in sympatric speciation of blind subterranean mole rats.