Spent grain is a valuable feed for cattle, as contains a high level of protein, slowly break down in the rumen, have a high P/Ca ratio and characterized by relatively low content of water-soluble carbohydrates.
The problem of using spent grain as feed is complicated by the fact that it contain a lot of moisture, which increases its transportation (per unit of dry matter mass), and also complicates its storage. The peak of beer production (and production of by-products of brewing, the main of which in quantitatively is spent grain) is in the summer period, when the demand for spent grain is seasonally reduced, whereas in winter, when there is a shortage of feed, average daily production volumes of spent grains falls by 3-4 times.
Based on these considerations, in the summer period it is rational to preserve spent grain in order to feed it in the winter. The most widely used method of preserving spent grain in the world is drying it. Dry spent grain is easier to transport and store. Nevertheless, in Western Europe, fresh raw or partially dehydrated by pressing spent grain is brought from breweries and fed it to livestock. For farms located close to the breweries, it is also advisable to use the preservation and storage of wet spent grain.
In recent decades, research has been conducted to find ways to silage raw spent grain, beyond drying it. One of the alternative methods of preserving spent grain is its silage. This method is complicated by the low dry matter content (about 12-25%) and low (about 1% calculated on dry matter) sugar content (Kuntzel, 1992), which are able to ferment relatively quickly during silage to form lactic acid. According to established views, the following conditions are most important for obtaining high-quality silage: a rapid decrease in the pH value of the juice of the silage mass to 4.0-4.2 and below; the presence of dry matter in the silage mass not less than 30% and ensuring the temperature of the silage mass in the range of 20-300C, and during storage of the silo - not above 150C. In addition, to prevent the development of mold and putrefactive bacteria in the silage mass, access to oxygen should be excluded. At the same time, should be considered that anaerobic conditions do not impede the development of most types of butyric acid bacteria, which are facultative anaerobes.
The pH level can easily be adjusted by fermenting sugars that includes in the composition of the silage mass, as well as by adding acids: organic - formic, propionic, acetic and inorganic - phosphoric and sulfuric. However, it should be noted that animals are reluctant to eat silage prepared with inorganic acids. At a relatively low pH, which is created due to the introduction of acids, fermentation can continue (a priori, it can be assumed that it will be lactic acid fermentation, while other types of fermentation will be inhibited, because lactic acid bacteria in anaerobic conditions withstand the lowest pH values - up to 3.2; the lower limit of pH is 3.0) or will be inhibited - depending on the amount of acid added.
Since the mentioned acids, both organic and mineral, are very aggressive liquids, and low molecular organic acids, in addition, are very volatile and have a sharp unpleasant odor, for use them in preservation, they were tested and found practical use acids with bacteriostatic effect at relatively low concentrations, and in addition, non-volatile: benzoic and salicylic, as well as salts of low-molecular organic acids.
Obviously, it is most appropriate to use preservatives that are non-aggressive, non-volatile, environmentally friendly and which can be used in animals body as nutrients elements. Those are the oldest preservatives: sugar and salt (both are used to increase osmotic pressure in the fluids of the preservation product). However, in silage (fermentation) sugar (including that present in the feed) is transformed into another preservative, no less ancient and even more effective because it has a strong bacteriostatic effect - lactic acid.
It is important that the conversion of sugar into lactic acid is accompanied by a loss of free energy, which is only about 5% of the energy contained in glucose and released during aerobic cleavage (Leininger, 1985). In addition, lactic acid is a more "convenient" nutrient than sugar, since in a rumen, under certain conditions, it can turn into propionate, which is used for glucose synthesis (which is the only precursor of lactose and is generally an essential metabolite in mammalian organism), whereas from the sucrose entering the rumen produces quite a lot of butyric acid, in the rumen wall metabolized to 3-hydroxybutyrate, the main of ketone bodies of ruminant.
