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Cumulative gas production: how to measure it, and what it can and cannot tell you
Published online by Cambridge University Press: 27 February 2018
Summary
The three most important factors describing the nutritive value of ruminant feeds are: feed intake, rumen fermentation, and enzymatic digestion. Animal experiments are usually expensive and time-consuming, so many in vitro techniques have been developed which are supposed to assist in the prediction of nutritive value, usually of rumen fermentation. One of these is the measurement of gas production from the substrate when incubated with a specific inoculum. The cumulative gas production technique measures gas at regular intervals in time, as an indicator of the kinetics of fermentation. The resultant cumulative gas profiles, fitted to specific equations, and in combination with other end-products (i.e. VFA and NH3) can indicate both the rate and extent of fermentability of the test substrates. This information can be used to compare substrates with each other. However, the fact that the technique has not yet been standardized, and that inoculum varies according to time and place, means that comparison both between runs and locations, can be very difficult. Also, there are a number of aspects of the technique which will always mean that its resemblance to the in vivo situation must be limited. Some of these limitations and other important considerations of the technique are described in this review.
Resumen
Los tres factores más importantes para describir el valor nutritivo de los alimentos para rumiantes son: consumo, fermentación en rumen y digestion enzimática. Los experimentos con animales son normalmente caros y consumidores de tiempo, por lo que muchas técnicas in vitro han sido desarrolladas en el supuesto de ayudar en la predicción del valor nutritivo, generalmente de valor de fermentación. Una de estas técnicas es la producción de gas a partir de un sustrato que es incubado con un inóculo específico. La técnica de producción de gas mide el gas, a intervalos regulares, como indicador de la cinética de fermentación. Los perfiles de producción de gas resultantes, descritos por ecuaciones específicas, y en combinación con otros productos terminales (ejem. Ácidos grasos de cadena corta y NH3) pueden describir tanto la tasa como el potencial de fermentación de los sustratos evaluados. Esta información puede ser empleada para comparación entre sustratos. Sin embargo, el hecho de que la técnica no ha sido todavía completamente estandarizada, y que el inóculo varía de acuerdo al tiempo y lugar, significa que la comparación entre experimentos en un mismo laboratorio y entre laboratorios puede ser muy difícil. También, existen muchos otros aspectos de la técnica que dejan claro que su semejanza a la situación in vivo será siempre limitada. Algunas de estas limitaciones y otras consideraciones importantes de la técnica son descritas en esta revisión.
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- Copyright © British Society of Animal Science 2006
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