Variation of the microbial biomass in in vitro gas assays with different substrates

FERNANDEZ TURREN, G.; KOZLOSKI, G.V.; CAPELESSO, A. ; POZO, C.

Congreso; 51st Annual Meeting of the Brazilian Society of Animal Science; 2014

The efficiency of microbial protein synthesis is a relevant variable in ruminant nutrition. It is usually measured in in vivo trials which, however, are expensive and require high analytical demand. Alternatively, in vitro systems are a practical and low cost tool used to simulate rumen fermentation, but it is not well established if it allows such determinations. The aim of the present study was to evaluate the impact of substrate type on the dynamics of the microbial biomass in an in vitro gas system. The study of microbial biomass variation was based on the variation of purines content in the flask throughout the incubation period. The tested substrates were starch, casein and cellulose (Avicel). For each substrate three runs were conducted. In each run and for each incubation time, samples were incubated in triplicate. Approximately 0.5 g of sample was weighed in 120 mL glass bottles and incubated with 50 mL buffer solution plus rumen inoculum (4:1) during 6, 12, 18, 24, 36, 48 or 72 h, in a slow-stir water bath at 39°C. After the respective incubation times, the total content of each bottle was dried in an air forced-oven at 70°C for at least 48 h. The content of purines in the dry residue was analyzed by spectrophotometry after acid digestion and precipitation with silver nitrate. Total gas production after 72 h of incubation was higher (P