Effect of Glucose Fermentation on Fiber Digestion by Ruminal Microorganisms In Vitro

Abstract

Two in vitro digestion trials were performed to determine whether the negative effect on fiber digestion when pH was maintained at > 6.2 was attributable to glucose alone or to end products of glucose fermentation. In some treatments, glucose was depleted by a previous 6-h incubation; the supernatant from this incubation was used as the buffer source for treatments using the fermented glucose medium. In trial 1, mixed cultures were grown on cellulose, soybean hulls, and corn bran in fresh media with 0 (control) or 25 mM glucose, in media previously fermented for 6 h with 0 (control) or 25 mM glucose, or in fermented control medium plus 25 mM lactic acid. The rate of NDF digestion was decreased with fermented glucose medium but not with fresh glucose medium or lactic acid medium. Concentrations of lactate, propionate, and butyrate did not appear to affect NDF digestion directly. In trial 2, six treatment media were used: control and glucose media that were either fresh or previously fermented for 6 h and fermented control and glucose media treated with a protease. Rate of NDF digestion was slower in cultures with fermented glucose medium that was treated with protease than in fermented control medium without protease. When treated with protease, rate of NDF digestion was not different between the fermented control medium and the fermented glucose medium. Thus, the negative effect on fiber digestion appeared to be attributable partially to a proteinaceous inhibitor that was produced in culture media containing a rapidly fermented sugar.

In vitro determination of ruminal dry matter and cell wall degradation, and production of fermentation end-products of various by-products

“…Thus, the lactic acid concentration of the giant pumpkin, orange peel and brewer's grain fermentations tended (P < 0.05) to decrease when the incubation time was increased. This result was similar to that of Piwonka and Firkins [28], which indicated that lactic acid could be partially fermented; they reported that the in vitro digestion trials contain bacteria that use lactic acid, as expected in a mixed culture from the rumen, and that lactic acid is fermented to propionate (30 to 35%) and butyrate (65 to 70%). Even so, the lactic acid of the fermentations of other by-products, such as red pepper, melon, broccoli, fresh artichoke and lemon peel were not affected (P > 0.05) by incubation time, except boiled artichoke.…”

Degradação in vitro da fibra em detergente neutro de forragem tropical de alta qualidade em função da suplementação com proteína e/ou carboidratos

“…No primeiro caso, reduções significativas no pH ruminal são responsáveis pela inibição parcial da degradação fibrosa por comprometerem a condição ideal de meio para crescimento dos microrganismos fibrolíticos (Mould et al, 1983;Hoover, 1986;Van Soest, 1994 Tabela 3 -Estimativas da taxa fracional comum para latência e degradação (λ), taxa fracional de degradação da FDNpd obtida a partir da conversão do parâmetro λ (c'), valor relativo da taxa de degradação (VRTD) e tempo de latência discreta (L) para a degradação ruminal da fibra em detergente neutro potencialmente degradável (FDNpd) e desvios-padrão assintóticos (DPA) para os perfis de degradação ajustados em função da suplementação proteica e/ou com carboidratos danosos à atividade microbiana sobre os carboidratos fibrosos da forragem (Mould et al, 1983;Hoover, 1986 (El-Shazly et al, 1961;Mertens & Loften, 1980;Piwonka & Firkins, 1993;Haddad & Grant, 2000;Arroquy et al, 2005) e recentemente relatados em condições de forragem tropical de baixa qualidade (Costa et al, 2008).…”

“…Por outro lado, alguns autores têm observado inibição da atividade de enzimas fibrolíticas na presença de amido no meio (Hiltner & Dehority, 1983, citados por Arroquy et al, 2005Piwonka & Firkins, 1993), fato que parece estar associado a liberação de compostos inibidores pelos microrganismos Tabela 4 -Máxima taxa de degradação (μ -h -1 ), taxa de crescimento específico de microrganismos (Sgr -h -1 ) e eficiência de crescimento microbiano a FDN potencialmente degradável da forragem (EFM -g MS microbiana/kg de carboidrato degradado no rúmen) em função da suplementação proteica e/ou com carboidratos que degradam o amido (El-Shazly et al, 1961), os quais parecem ser de natureza proteica (bacteriocinas) (Piwonka & Firkins, 1993;Kalmokoff et al, 1996). A união destes argumentos implicaria redução na degradação da FDNpd na presença de amido como suplemento exclusivo, como verificado neste trabalho (Tabelas 3 e 4).…”

Degradação in vitro da fibra em detergente neutro de forragem tropical de baixa qualidade em função de suplementação com proteína e/ou carboidratos

“…De forma geral, como discutido anteriormente, efeitos deletérios sobre a utilização da FDNpd foram observados com a suplementação com amido (Tabela 3), comportamento que concorda com relatos de outros autores (ElShazly et al, 1961;Mertens & Loften, 1980;Piwonka & Firkins, 1993;Haddad & Grant, 2000;Arroquy et al, 2005).…”