In vitro methods of feed evaluation have numerous advantages over in vivo methods. They are less expensive, less time-consuming and allow incubation conditions to be maintained more precisely than in vivo. In addition, in vitro techniques utilize small amounts of test feeds making them applicable to screening of feeds that are not available in sufficient quantity for in vivo experiments. There are a number of factors that affect fermentation of feeds in vitro and could cause intra- or inter-laboratory differences. These are mainly associated with the nature of rumen fluid inoculum, although breed of animal, its physiological condition, diet, time of feeding, time of collection of rumen fluid relative to feeding time, method of rumen fluid collection (i.e. liquid or solid phase), and time elapsed between rumen fluid sampling and inoculation are all factors that have been shown to influence microbial activity in vitro. The quantitative extent of the influence of combined effects of these factors is complex and it is not possible to quantify their influence on any specific in vitro system. Attempts to completely standardize in vitro techniques to reduce or eliminate the influence of these factors is not practical due to procedural differences required by laboratories in different parts of the world to meet locally available resources. However, it is important that in vitro techniques used around the world be sufficiently robust to overcome local modifications to yield similar results. This paper presents a study on intra- and inter-laboratory variability of an in vitro gas production procedure, and calculate metabolisable energy values of feeds, in several laboratories in different geographical locations in the world that use the same protocol of in vitro gas production technique.
Getachew et al. (2002) "Laboratory variation of 24 h in vitro gas production and estimated metabolisable energy values of ruminant feeds", Animal Feed Science and Technology, 102, 169-180
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