Principles of techniques that rely on gas measurement in ruminant nutrition

Abstract

In vitro gas production techniques have become popular for characterizing the rate and extent of digestion of ruminant foods. In a typical gas production study, gas (predominantly carbon dioxide) is produced as particles of substrate are fermented by rumen micro-organisms in a bicarbonate buffered culture medium. Innovations in equipment design, including automated pressure recording systems and mathematical descriptions of the gas production profiles themselves, make the techniques both simple and precise and therefore good as laboratory procedure. The technique of measuring gas is of value in ruminant science because the kinetics of gas production and substrate degradation are very closely correlated. However, although it is relatively easy to measure gas volumes and to determine the kinetics of gas production, the underlying processes that give rise to the gas in the first place are complex and not well understood. Therefore, there is concern about what is being measured in gas production studies and how this relates to the digestion process in the ruminant animal. In this paper we review some of the fundamental properties of gases, describe their behaviour in liquids and consider some of the biological and chemical factors influencing gas production. From a knowledge of how gases behave in liquids and at gas-liquid interfaces, both at ambient and increased temperatures and pressures, it is possible to deduce what is happening in gas production studies. However, although the technique is invaluable for obtaining information about the digestion of particulate substrates in anaerobic ecosystems, we conclude that gas production should be used with caution in routine food evaluation studies.

Diversity and activity of enriched ruminal cultures of anaerobic fungi and methanogens grown together on lignocellulose in consecutive batch culture

“…Although the kinetics of fibre degradation was not assessed in this study, the results indicated that the anaerobic fungi were able to degrade more fibrous substrate in the presence of methanogens than in their absence. The co-cultures produced more gaseous end-products relative to the fungal cultures alone, and this has been correlated to enhanced fibre degradation (Theodorou et al, 1998).…”

Effects of season, browse species and polyethylene glycol addition on gas production kinetics of forages in the subhumid subtropical savannah, South Africa

“…The in vitro gas production technique has become accepted for evaluating forage digestion features and fermentation kinetics . It has been commonly applied for determining the nutritive value of feeds .…”

“…12 The in vitro gas production technique has become accepted for evaluating forage digestion features and fermentation kinetics. 13,14 It has been commonly applied for determining the nutritive value of feeds. 15 More recently, the increased interest in alternative resources of ruminant feed has led to an increase in use of the gas production technique as a result of the benefit in assessing fermentation kinetics.…”

The effect of sample grinding procedures after processing on gas production profiles and end‐product formation in expander processed barley and peas

“…These techniques were developed to predict fermentation of ruminant feeds21 and are widely used to study the degradative behaviour of feeds, evaluate microbial fermentation of ruminant feeds,22 estimate short chain fatty acid production,23 estimate the production of methane,24 and rank the fermentability of feedstuffs 25. As with other laboratory methods, many factors, such as the pressure of the head space of the fermentation vessels,26 atmospheric pressure,27 the type of apparatus,21 the sample size and preparation,1, 4, 5 hydrating the samples with the medium before inoculation,28 and the source of inoculum,29, 30 may affect the gas production profiles. In the upcoming paragraphs we have tried to elaborate on whether different grinding procedures and sample preparations in the technologically processed feeds have any effect on particle size distribution and consequently on the gas production profiles and formation of fermentation end products.…”