ARTICLE FEED & ADDITIVE MAGAZINE April 2023 79 these amino acids remain fairly stable at the same time. Therefore, the responses of only one single reference amino acid -usually lysine- to changing production conditions have to be evaluated while the remaining amino acids are then to be adjusted simply by calculation. Only essential amino acids are considered in this concept. However, there is still a scientific discussion about the adequate ratio between essential and non-essential amino acids especially in low protein diets. Lysine is the reference amino acid. In swine nutrition lysine has been established as reference amino acid mainly because lysine is the first-limiting amino acid in swine diets. Although this is not the case in common broiler diets – here methionine and cystine (Met+Cys) are first-limiting in most cases – lysine (Lys) is taken as the reference amino acid as well supported by the following three arguments: Lys is almost exclusively utilised for body protein accretion and thus requirement is only affected very little by other metabolic functions (maintenance requirement) or feathering as this is the case for Met+Cys. There are no metabolic interactions between Lys and other amino acids. In contrast, Met can be converted to Cys by the bird but the opposite way is not possible. From the analytical perspective, it is easier to analyse Lys than Met and particularly Cystine. THERE ARE VARIOUS WAYS TO DETERMINE AN “IDEAL AMINO ACID PROFILE” Different scientific approaches to obtain ideal amino acid profiles have been described. One method is simply to review literature: The results of all available experiments designed to determine the requirement for individual amino acids are compiled and the average optimum amino acid levels are then presented as ideal amino acid profile. However, due to differences regarding the experimental conditions, e.g. environment, climate, housing system, stocking density, diet composition, a number of possible factors and inaccuracies affecting amino acid ratios are not considered properly. Although not explicitly presented as ideal ratios to Lys, the amino acid recommendations for broilers by NRC (1994) might serve as an example for this method. The factorial approach, multiple dose-response experiments investigating the full range of essential amino acids simultaneously, or the deletion method are more sophisticated methods to obtain ideal amino acid profiles. IDEAL AMINO ACID RATIOS MIGHT BE AFFECTED BY ENVIRONMENTAL ISSUES Comparing the outcome of all the different approaches above to determine ideal amino acid ratios, the obtained amino acid profiles are surprisingly similar - disregarding their advantages and
RkJQdWJsaXNoZXIy MTUxNjkxNQ==