Abstract
ABSTRACT: In vitro gas production techniques represent a valuable tool to describe the kinetics of ruminal degradation of food. However, the ruminal liquor used as a microbial inoculum has been a great source of variation and error. A standardization of this factor should contribute to assure the independence of food fermentation parameters from those of the inocula. In this research it was hypothesized that a controlled pre-incubation treatment of ruminal liquor could contribute to stabilize and homogenize the undigested residues of blanks and as a consequence, of the production of residual cumulative gas production (CGP). A pre-incubation (i.e. previous real incubation) of rumen inocula was developed with a simple substrate similar to the diet offered to donors at 1% w/v for 0, 1, 2 and 4 h (Control, Prei-1, Prei-2 and Prei-4 treatments respectively). Once the pre-incubation hours were completed, they were incubated with contrasting substrates and without substrate (i.e. blanks) in order to evaluate the CGP, in vitro digestibility of the DM and fermentation products. Although, the fermentative activity of the pre-incubated inoculums worked satisfactorily in the in vitro system, contrary to what was speculated, residues of the pre-incubation increased the variability and heterogeneity of variances among blanks. Consequently, it was concluded that the pre-incubations did not work to generate more homogeneous and less variable ruminal liquor for the in vitro gas production system.
Highlights
RESUMO: Técnicas de produção de gás in vitro representam uma ferramenta valiosa para descrever a cinética de degradação ruminal dos alimentos
In vitro gas production techniques are widely employed to offer a repetitive, economical and applicable laboratory technique to estimate in vitro dry matter digestibility, based on the correspondence between dry matter degradability and cumulative gas production (CGP, MOULD et al, 2005)
The husbandry conditions of experimental animals (RYMER et al, 2005) and their diet (BOGUHN et al, 2013) are parameters which require more control if we look for standard conditions in the system
Summary
8.9 ns aParameters: A: Fraction rapidly disappeared; B: Fraction disappeared at a constant fractional rate per unit time and c: Rate of B. t1, CGP to hour 1; t1-t24, CGP from hour 1 to hour 24; t24, CGP at 24 h. In order to generate trustable data there must exist a balance between inocula microbial activity and their reproducibility among different laboratories and times (CORNOU et al, 2013), in this sense CGP of blanks must be significantly different from zero (as an expresion of microbial activity), and should present low variability among replicates within incubation batchs while representing a low proportion of CGP of the assessed samples In this sense, our preincubation treatments almost doubled Control CGP at 24 h (15.9, 14.0, 12.3 and 7.9, ml, for Prei-1, Prei-2, Prei-4 and Control) reflecting a media environment more favorable for microbial fermentation and reaching close to the minimum CGP for blanks recommended by NAGADI et al (1999; i.e. 15.5 ml in 24 h). GETACHEW et al (2005) tested eight different commercial dairy concentrates and even though VFA profiles were lower than those reported here, the relationship between acetic/propionic was similar (i.e. 2.4 and 2.1, for the 8 rations and CON, respectively) This similar behavior of Pre-i and Control on fermentation kinetics, ivDMD and ruminal environment were coherent with the characteristics of a normal inoculum (DIJKSTRA et al, 2005)
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