Volatile Fatty Acids Synthesis Research Articles

ASSESSMENT OF METHANE ESTIMATION FROM VOLATILE FATTY ACID STOICHIOMETRY IN THE RUMEN IN VITRO

Rumen microbes breakdown feed to produce volatile fatty acids (VFA), carbon dioxide, ammoniaand methane (CH4). Metabolic hydrogen in the form of reduced protons is used during CH4 formation aswell as during VFA synthesis. Therefore, VFA concentration in the rumen may stoichiometrically berelated to CH4 emission. The aim of this study was to evaluate methane emission between experimentaland model estimates. Two stoichiometrical models for predicting CH4 from VFA were assessed, i.e.Moss et al. (2000) and Hegarty and Nolan (2007) models. The data sets were obtained from a publishedliterature. Samples used were leaves from 27 tropical plant species. Prediction error was conducted bycomputing root mean square prediction error (RMSPE). Results showed that estimation model of Mosset al. (2000) had lower RMSPE value, i.e. 8.01%, than that of Hegarty and Nolan (2007) model, i.e.10.73%. Variation of methane emission, i.e. the low or high methane can be estimated by VFAcomposition with a sufficient accuracy. Adjusment by considering H2 recovery lowered the biassignificantly. It can be concluded that Moss model had better accuracy in predicting CH4 emission fromVFA composition than that of Hegarty and Nolan model.

Rheology of aging, concentrated, polymeric suspensions: Application to pasty sewage sludges

The rheological behavior of pasty sewage sludges from different origins and at different ages of fermentation has been studied on the basis of careful rheometrical tests. These materials appear to be basically yield stress fluids whose flow curves can be fairly well represented by a Herschel–Bulkley model. The yield stress existence is evidenced by a clear transition between a viscoelastic and a viscous behavior at a critical shear stress. The rheological parameters are shown to mainly depend on the organic fraction and the time of fermentation. By extracting the main solids components (minerals, proteins, lipids, carbohydrates) we show that the behavior evolution is governed by the synthesis of volatile fatty acids.

The effect of grinding and pelleting on the digestion of Italian ryegrass and timothy by sheep.

1. Primary growths of Italian ryegrass and timothy were harvested in late May, high-temperature dried and either retained in the chopped form or ground through a 2 mm sieve and pelleted. All diets were fed to four sheep fitted with re-entrant cannulas into the proximal duodenum and measurements of the sites of energy and protein digestion and the synthesis of volatile fatty acids (VFA) and microbial protein were made. 2. Grinding and pelleting significantly reduced rumen digestion of organic matter and structural carbohydrate (P less than 0.05) and the synthesis of rumen VFA (P less than 0.01), whilst significantly more digestion occurred in the hind gut, although this was not sufficient to prevent a decline in over-all digestibility on the pelleted diets (P less than 0.05). The magnitude of all responses was much larger on the Italian ryegrass diet. 3. Net microbial protein synthesis was 15% less on the pelleted diets but efficiency of microbial protein synthesis was unaffected (mean 188 g/kg rumen digested organic matter). Pelleting reduced the degradation of dietary protein from 69% to 47%, and dietary protein represented significantly more of the total protein flowing to the duodenum on the pelleted diets (chopped 28%, pelleted 41%). 4. Over-all, grinding and pelleting reduced total absorbed energy supply by 10% but increased absorbed protein supply by 15% which may contribute to some of the improvements seen in the net energy value of pelleted diets.