It is time to update the old system of feedstuff nutrient evaluation to achieve precision nutrition.
The primary method for describing the gross nutrient composition of feed ingredients and feeds has changed little since the US Food and Drug Administration adopted the “proximate analysis” method in 1888. As analytical chemistry advanced, the knowledge of feed composition improved, and separate requirements were determined for each new nutrient, mineral, vitamin, amino acid, and some essential fatty acids.
However, the proximate analysis has persisted for the feedstuff trade and for estimating the energetic contributions of feed ingredients.
Feed chemistry was in its’ infancy when the proximate analysis, or Weende Method, was conceived in the city of Weende, in the Hanover Kingdom, in the 1860’s. The true nature of proteins and the other constituents was unknown. Dividing feed ingredients into the crude albuminous material, or protein, ether extract, crude fiber, and ash fractions, was state of the art then. Whatever was left over was called the “nitrogen-free extract” despite not being an extract at all. It was supposed to represent soluble or available carbohydrates.
The proximate analysis method has some helpful features. For instance, the nitrogen-free extract is found by difference, so the analytical results always add up to 1,000.00 g/kg. In reality, there are no perfect methods for chemically defining feed ingredients. Using one technique or set of techniques for analyzing all ingredients should not be expected to give perfect answers every time.
Finding and understanding why the composition of ingredients does not sum to 1,000 g/kg should lead to a better understanding of just what is in all the different feed ingredients.
The difficulty in describing feed ingredients is due to the great variety of nutrients and other chemicals across and within plant and animal species.
The proteins in each ingredient have different amino acids. Consequently, the proteins’ nitrogen and energy contents are unique for each ingredient. Starch from different strains of even one crop type, like maize, will have different branching among their glucose units and different molecular weights and physical properties. For instance, dent corns are used for feed, while waxy corns are used to make corn starch for food and corn gluten feed for animals.
The same applies to oligosaccharides, non-starch polysaccharides, pectins, lignin, an...
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