Dry matter represents everything contained in a feed sample except water; this includes protein, fiber, fat, minerals, etc. In practice, it is the total weight of feed minus the weight of water in the feed, expressed as a percentage. It is determined by drying the feed sample in an oven until the sample reaches a stable weight. This is normally a simple analysis. However, estimates of the DM of fermented materials such as silage are complicated by the presence of volatile fatty acids. These acids are removed in the drying process but they are part of the dry matter and are digestible. This introduces a variable amount of error. Analysis of the fodder without ensiling provides a more accurate estimate of fiber fractions and digestibility contained in the silage.