First use of triply labelled water analysis for energy expenditure measurements in mice.

The doubly labelled water (DLW) method is widely used to determine energy expenditure. In this work, we demonstrate the addition of the third stable isotope, 17O, to turn it into triply labelled water (TLW), using the three isotopes measurement of optical spectrometry. We performed TLW (2H, 18O and17O) measurements for the analysis of the CO2 production (rCO2) of mice on different diets for the first time. Triply highly enriched water was injected into mice, and the isotope enrichments of the distilled blood samples of one initial and two finals were measured by an off-axis integrated cavity output spectroscopy instrument. We evaluated the impact of different calculation protocols and the values of evaporative water loss fraction. We found that the dilution space and turnover rates of 17O and 18O were equal for the same mice group, and that values of rCO2 calculated based on 18O-2H, or on 17O-2H agreed very well. This increases the reliability and redundancy of the measurements and it lowers the uncertainty in the calculated rCO2 to 3% when taking the average of two DLW methods. However, the TLW method overestimated the rCO2 compared to the indirect calorimetry measurements that we also performed, much more for the mice on a high-fat diet than for low-fat. We hypothesize an extra loss or exchange mechanism with a high fractionation for 2H to explain this difference.

Distinct Effects of Short Chain Fatty Acids on Host Energy Balance and Fuel Homeostasis With Focus on Route of Administration and Host Species.

Accumulating evidence implicates gut-microbiota-derived metabolites as important regulators of host energy balance and fuel homeostasis, the underlying mechanisms are currently subject to intense research. In this review, the most important executors, short chain fatty acids, which both directly and indirectly fulfill the interactions between gut microbiota and host will be discussed. Distinct roles of individual short chain fatty acids and the different effects they exert on host metabolism have long been overlooked, which compromises the process of clarifying the sophisticated crosstalk between gut microbiota and its host. Moreover, recent findings suggest that exogenously administered short chain fatty acids affect host metabolism via different mechanisms depending on the routes they enter the host. Although these exogenous routes are often artificial, they may help to comprehend the roles of the short-chain-fatty-acid mechanisms and signaling sites, that would normally occur after intestinal absorption of short chain fatty acids. Cautions should be addressed of generalizing findings, since different results have appeared in different host species, which may imply a host species-specific response to short chain fatty acids.

Effects of different levels of rapeseed cake containing high glucosinolates in steer ration on rumen fermentation, nutrient digestibility and the rumen microbial community.

This trial was conducted to study the effects of dietary rapeseed cake (RSC) containing high glucosinolates (GLS) on rumen fermentation, nutrient digestion and the rumen microbial community in steers. Eight growing steers and four rations containing RSC (GLS 226·1 µmol/g DM) at 0·00, 2·65, 5·35 and 8·00 % DM were assigned in a replicate 4 × 4 Latin square design. The results indicated that increasing RSC levels increased the ruminal concentration of thiocyanate (SCN) (P < 0·01), decreased the ruminal concentration of ammonia nitrogen (NH3-N) and the molar proportion of isovalerate (P < 0·05), did not affect the ruminal concentration of total volatile fatty acids (P > 0·05), decreased the crude protein (CP) digestibility (P < 0·05) and increased the ether extract (EE) digestibility (P < 0·01). Increasing RSC levels tended to decrease the abundances of ruminal Ruminobacter amylophilus (P = 0·055) and Ruminococcus albus (P = 0·086) but did not affect methanogens, protozoa, fungi and other bacteria (P > 0·05). Increasing RSC levels in the ration did not affect the ruminal bacterial diversity (P > 0·05), but it increased the operational taxonomic units and the bacterial richness (P < 0·05) and affected the relative abundances of some bacteria at the phylum level and genus level (P < 0·05). In conclusion, RSC decreased the ruminal concentration of NH3-N and the CP digestibility, increased the EE digestibility and partly affected the ruminal bacterial community. SCN, as the metabolite of GLS, could be a major factor affecting these indices.