Raw material and nutrient lexicon

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Energy

The energy of a feedstuff results primarily from the carbohydrates and fats it contains, but also partly from the protein. The energy required by the animal's metabolism is obtained from these nutrients through a wide variety of conversion processes. When it comes to the energy requirements of animals, a distinction is made between the maintenance requirement and the performance requirement. The maintenance requirement indicates the amount of energy that the animal needs to maintain the most elementary bodily functions. The performance requirement indicates how much energy must be supplied to the animal in order to be able to achieve a certain performance. Maintenance requirement and performance requirement together give the total requirement that the animal needs to achieve performance and maintain its bodily functions. Ultimately, in order to provide the animal with a sufficient amount of energy to meet its total needs, the supply of sufficient of the above nutrients is essential. The energy rating of a feed for animal nutrition is based on the conversion of the energy resulting from the nutrients in the animal's metabolism. Thegross energy (GE) content of a feed ultimately represents its calorific value and can be determined in the laboratory in the so-called bomb calorimeter. The gross energy is not a suitable assessment standard for animal nutrition because the level of digestibility and the type of digestion (by endogenous or microbially formed enzymes) varies greatly.

Part of the gross energy is excreted with the faeces. This part is predominantly dependent on the plant-anatomical and -histological structure of the framework substances present in the feed. If this loss is subtracted from the gross energy, thedigestible energy (DE) is obtained. On this basis, the energetic feed value for horses and rabbits is assessed.

Of the digestible energy, a further part is lost to the organism through energy-containing excretions with the urine and, in the case of ruminants, additionally through fermentation gases. This loss is also influenced by the type of ration or feed given. If the digestible energy is reduced by this proportion, we speak of themetabolizable energy (ME). For monogastric animals(pigs, poultry), an assessment at this level essentially takes into account all energy losses caused by the feed. This does not include thermal energy, which is produced by microbial conversions in the digestive tract and cannot be used by the animal. In ruminants, the fermentation heat released in the forestomachs (rumen) and contained in the convertible energy is considerably greater. By determining the convertible energy, a meaningful energy assessment is possible for monogastric animals, poultry and young growing ruminants. Differences in the utilisation of metabolizable energy in the metabolism for different performances (maintenance, growth, milk production) can be taken into account when determining the requirement. The energetic feed evaluation for pigs, poultry, calves, rearing cattle, fattening cattle, dogs and cats is based on the convertible energy.

When the convertible energy is converted in the maintenance metabolism or into a specific output, non-usable thermal energy is released, which depends on both the animal species and the type of output (protein or fat synthesis). Taking these into account leads to thenet energy(NE) for the respective output. Consequently, there is not one net energy, but only one for maintenance (NEm) or for fat formation (NEf) or for milk formation (NEl). The energetic feed evaluation for dairy cows is based on the "net energy lactation" (NEL). The physical unit for gross energy, digestible energy, convertible energy and net energy is the joule (J). Corresponding concentrations are given as "kilojoules (kJ)" or "megajoules (MJ)".

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