Published online by Cambridge University Press: 27 February 2018
When a food is ingested by a ruminant animal, the carbohydrate fraction of the food is fermented by the rumen micro-organisms to produce gas (predominantly carbon dioxide and methane) as well as volatile fatty acids (VFA). The gas production technique simulates this fermentation process and provides an estimate of both the rate and extent of fermentation. Comparing the gas production (GP) profiles of foods enables a comparison to be made of the fermentative characteristics of different foods. However, the technique uses a bicarbonate-based medium system with the rumen liquor. This complicates the GP profile because of the production of ‘indirect’ gas resulting from the reaction between the VFA and the bicarbonate ions.
Beuvink and Spoelstra (1992) measured the volume of gas produced from buffered rumen fluid when known amounts of VFA were added and observed that 20·8 ml gas were released per mmol VFA. However, there is variation between laboratories in terms of the composition of the medium that is used. Even when the same medium is used, significant differences have been observed in the GP profile when different types of apparatus were employed (Rymer and Givens, 1997). Media are gassed with carbon dioxide before they are added to the gas production system and it is possible that the concentration of carbon dioxide dissolved in the medium varies between experiments. The objective of this experiment, therefore, was to determine whether the volume of indirect gas produced was affected by the composition of the medium, the addition of carbon dioxide, and the technique employed to measure gas production.
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