Pre-incubation of ruminal inocula to assess in vitro gas production and digestibility

EnglishIn 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 portuguesTecnicas de producao de gas in vitro representam uma ferramenta valiosa para descrever a cinetica de degradacao ruminal dos alimentos. No entanto, o liquido ruminal utilizado como inoculo microbiano tem sido uma grande fonte de variacao e erro. A padronizacao deste fator deve contribuir para garantir a independencia dos parâmetros de fermentacao dos alimentos a partir dos inoculos. Neste trabalho, hipotetizou-se que um tratamento controlado de pre-incubacao do liquido ruminal poderia contribuir para estabilizar e homogeneizar os residuos nao digeridos dos brancos e, como consequencia, da producao de producao cumulativa de gas residual (CGP). Uma pre-incubacao (ou seja, incubacao real previa) dos inoculos do rumen foi desenvolvida com um substrato simples semelhante a dieta oferecida aos doadores a 1% p/v por 0, 1, 2 e 4 h (Controle, Prei-1, Pre- 2 e Prei-4 tratamentos respectivamente). Uma vez completadas as horas de pre-incubacao, elas foram incubadas com substratos contrastantes e sem substrato (ou seja, brancos) para avaliar o CGP, a digestibilidade in vitro da MS e os produtos de fermentacao. Embora a atividade fermentativa dos inoculos pre-incubados tenha funcionado satisfatoriamente no sistema in vitro, ao contrario do que foi especulado, os residuos da pre-incubacao aumentaram a variabilidade e heterogeneidade das variâncias entre os brancos. Consequentemente, concluiu-se que as pre-incubacoes nao funcionaram para gerar um liquido ruminal mais homogeneo e menos variavel para o sistema de producao de gas in vitro