Abstract
Abstract. Recently, biological procedures for feed protein evaluation in pig and poultry diets have been based on the amino acid composition of feed ingredients considering the animal's losses during processes of digestion or total protein utilization in a different manner. Such a development towards individual amino acids (AAs) was inevitable according to the disadvantage of traditional protein quality measures, like biological value (BV) or net protein utilization (NPU), to be non-additive in complex animal diets. In consequence, such measures are generally not suitable for predicting the final protein quality of protein mixtures from the individual protein value of feed ingredients. Otherwise, recent measures of AA disappearance from the small intestine up to the end of the ileum (ileal AA digestibility) also do not provide a true reflection of the biological availability of individual feed AAs independent of the extent of taking into account endogenous AA losses during digestion processes. Sophisticated procedures for protein evaluation are needed considering the AA losses, both during absorption and utilization after absorption. Advantages and limitations of important developments in procedures are discussed. Accordingly, the development of an exponential modelling approach is described (the Göttingen approach), which overcomes some of the traditional disadvantages by measuring the individual AA efficiency. Connecting feed protein evaluation, the modelling of quantitative AA requirements, and improved ideal protein concepts offers different fields of application. In addition, as demonstrated by example, the modelling of nitrogen losses per unit protein deposition and the minimizing of this parameter yields a further interesting tool for lowering the nitrogen burden from protein utilization processes. Finally, it is pointed out that traditional laboratory procedures also need to be updated, adapted to current knowledge, and validated according to the increasing hurdles for animal studies from the viewpoint of animal welfare. Modelling is a procedure with the potential to reduce the number of experimental animals significantly. This development needs more attention, higher acceptance, and wider application in the future of protein evaluation.
Highlights
Today, the importance of valid protein evaluation systems in animal nutrition is not a point of dispute
Biological procedures for feed protein evaluation in pig and poultry diets have been based on the amino acid composition of feed ingredients considering the animal’s losses during processes of digestion or total protein utilization in a different manner. Such a development towards individual amino acids (AAs) was inevitable according to the disadvantage of traditional protein quality measures, like biological value (BV) or net protein utilization (NPU), to be non-additive in complex animal diets
In contrast to earlier reviews (Bock, 1975; Bergner, 1994), an extended focus on biological protein evaluation (Hackler, 1977) will overcome the excessive view on digestibilityrelated processes in the digestive tract. This current procedure is supported by the general view of Fuller (2012) who pointed out that digestibility is not the only determinant of nutrient bioavailability; an integration of factors is needed for factors that limit the extent of absorption and the availability of AA for metabolism
Summary
The importance of valid protein evaluation systems in animal nutrition is not a point of dispute. An extended number of indispensable amino acids (AA) have become more interesting as a feed additive to compensate for the suboptimal dietary supply of individual AAs. an extended number of indispensable amino acids (AA) have become more interesting as a feed additive to compensate for the suboptimal dietary supply of individual AAs This process yields lower nitrogen (N) loads which have to be eliminated from the animal’s metabolism by urea or uric acid synthesis. All these factors are a driving force for ongoing research on protein evaluation in animal nutrition.
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