Effect of pH and Energy Spilling on Bacterial Protein Synthesis by Carbohydrate-Limited Cultures of Mixed Rumen Bacteria

Abstract

Rumen contents were obtained from a cow fed 2.5 kg concentrates and 2.5 kg timothy hay twice daily, and the mixed rumen bacterial inoculum (pH 6.3) was separated from large feed particles and protozoa by centrifugation. Bacteria were incubated in artificial media at pH 6.7 and 6.0. When starch, sucrose, cellobiose, xylan, pectin, or a mix of carbohydrates were provided to pH 6.7 incubations at 1 mM/h for 10 h, fermentation was carbohydrate-limited, less than 20% of the carbohydrate was converted to lactate, molar ratio of methane to hexose fermented was as great as 49%, and pH remained constant. When initial pH was lowered to 6.0, methane production was nearly eliminated, volatile fatty acid production was reduced, and there was a small decrease (less than .5) in final pH. At pH 6.0, lactate production was increased in all incubations except xylan and pectin, and pH had a greater effect on acid production than the type of carbohydrate provided. Bacterial protein synthesis was reduced 34 to 69% when initial pH was 6.0, but these reductions were greater than decreases in carbohydrate utilization, increases in lactate, and associated decreases in adenosine 5'-triphosphate production. Because less adenosine 5'-triphosphate was used for protein synthesis, it appeared that low pH diverted energy to nongrowth functions.

Effects of Degradable Protein and Non-Fibre Carbohydrates on Microbial Growth and Fermentation in the Rumen Simulating Fermenter (Rusitec)

“…Total VFA and methane production were greater for pectin and high RDP treatments, which is in agreement with the observed increases of feed disappearance. Compared with starch treatment, pectin treatment produced greater molar proportion of acetate and lower propionate molar proportion, which is consistent with results obtained in previous studies (Marounek et al, 1985;Strobel and Russell, 1986). The methane production was greater for pectin treatment may also relate to the hydrolysis of methyl esters from pectin to produce methanol, which can be exclusively converted into methane and increase the rate of methanogenesis (Pol and Demeyer, 1988).…”

“…Compared with starch, pectin produced similar microbial N to several previous studies (Strobel and Russell, 1986;Chester-Jones et al, 1991). However, tendencies of NFC × RDP interaction were observed for microbial N flow in the present study.…”

“…Many studies have examined the effect of adding sucrose to dietary rations on microbial synthesis, but results remain inconclusive, with microbial protein production increased in some studies (Huhtanen, 1988;Chamberlain et al, 1993) but reduced in other studies (Hall and Herejk, 2001;Sannes et al, 2002). However, little data are available on the effect of pectin on microbial synthesis, though inconsistent results have also been reported in some studies (Strobel and Russell, 1986;Hall and Herejk, 2001). Heldt et al (1999) found that the impact of starch and sugars on lowquality forage utilization may interact with the amount of supplemental rumen degradable protein (RDP).…”

Farelo da vagem de algaroba em dietas para cabras lactantes: parâmetros ruminais e síntese de proteína microbiana

“…Os microrganismos produzem mais propionato quando o amido é fermentado, mais acetato a partir de substâncias pécticas e mais butirato a partir da sacarose (Strobel & Russell, 1986). Independentemente da fonte, o efeito do carboidrato no pH ruminal será, provavelmente, mais intimamente relacionado à sua taxa de produção de ácidos orgânicos (Leiva et al, 2000 Tabela 2 -pH ruminal e concentrações de nitrogênio amoniacal, acetato e propionato em cabras alimentadas com concentrado contendo farelo de vagem de algaroba em substituição ao fubá de milho valores de 9,49 e 3,13 mM para acetato e propionato, respectivamente.…”

Produção, composição, consumo e digestibilidade em vacas recebendo milho reidratado e ensilado com silagem de cana de açúcar como volumoso

“…O aumento na fermentabilidade do amido é sugerido como um causador de diminuição da digestibilidade de fibra dietética (KNOWLTON et al, 1998;THEURER et al, 1999), por diminuição do pH (BEAUCHEMIN et al, 2001;CORONA et al, 2006;DILORENZO et al, 2011) que é apontado como causa da diminuição da atividade de microrganismos fibroliticos (STROBEL;RUSSEL, 1986). Nossos resultados são similares descritos por Oba e Allen (2003c) os quais em estudo comparando dietas com silagem de grão úmido e milho moído seco em dois níveis de amido na dieta não observaram efeito sobre a digestibilidade da fibra dietética.…”