Studien zur Aminosäurenwirksamkeit beim Mastgeflügel unter spezifischer Betrachtung der verzweigtkettigen Aminosäuren

The ideal amino acid ratio (IAAR) offers one possibility to achieve the goals of an environmentally compatible animal production. The IAAR defines the exact ratio of amino acids (AA) that are required by an animal for a given desired performance, e.g. growth, reproduction, etc. Ideally, no AA is in a limiting or exceeding position. Consequently, all AA are equally limiting. Under such circumstances, the protein can be utilized with the highest efficiency. Nitrogen (N) – excretions as well as the impact on the metabolic burden are decreased. In the concept of the IAAR, the AA under investigation is related to a reference AA, mostly lysine (Lys). A thorough literature research showed that information about an IAAR for the branched-chain amino acids (BCAA) leucine (Leu), isoleucine (Ile), and valine (Val) for meat type chickens are scarce, especially regarding the Leu:Lys-ratio. The aim of this study was the determination of an IAARBCAA for male broiler chickens (Ross 308), followed by a validation of the derived results. Therefore, data analysis applied a non-linear N-utilization model for growing monogastric animals. Furthermore, the optimal timeframe for taking a blood sample to determine the branched-chain α-keto acids in blood plasma of broiler chickens was assessed. Consequently, three consecutive experiments were carried out. Each experiment consisted of an N-balance study and a growth assay. Every N-balance study was separated into an adaptation period (5d), followed by two consecutive collection periods (2 x 5d) for starter and grower period, respectively. While the starter period lasted from the 10th to 20th day of life (N = 36), the grower period, utilizing new birds, lasted from 25th to 35th day of life (N = 36). During the growth assay, growth periods lasted from the 1st to 12th; 13th to 24th and 25th to 36th day of life in Experiment 1. In Experiment 2 and 3, starter period lasted from the 1st to 21st day of life and 10th to 20th day of life, respectively,and grower period from 21st to 35th and 25th to 35th day of life, respectively. Each growth period used 240 chickens. At the beginning and the end of each growth period, representative animals were chosen for whole body analysis, fasted for 24 hours, euthanized, autoclaved, homogenized and analyzed for CP, DM and crude ash. This enabled the calculation of the animals´ N-deposition for the respective growth period. Wheat, wheat gluten, soy protein concentrate and fish meal were the main feed ingredients. The applied IAAR was calculated based on literature data. Diet formulation was based on the principle of the diet dilution technique. For assessing the optimal time to take blood samples, 40 animals which had access to an AA-balanced diet were utilized. On day 36, blood samples were taken over a graded period of time. The content of the α-branched-chain keto acids was determined by high performance liquid chromatography. The results of the individual experiments are presented below. In Experiment 1, the daily N maintenance requirement (NMR) and the daily theoretical maximum of N-retention (NRmaxT) were determined for data evaluation based on the non-linear N-utilization model. An NMR and NRmaxT of 113 mg N/LMkg0,67/d and 4705 mg N/LMkg0,67/d could be derived for the starter period, while values of 215 mg N/LMkg0,67/d and 4516 mg N/LMkg0,67/d were concluded for the grower period. Furthermore, based on the Lys-efficiency, the Lys-requirement was determined, taking into account varying levels of performance (g CP-deposition/d), feed intake (g/d) and body weight. In Experiment 2, the IAAR for the BCAA, related to Lys was derived (IAARBCAA). An IAARBCAA for the starter and grower period of Lys:Leu:Ile:Val = 100:94:55:65 and 100:106:56:72 was derived, respectively. These results indicated a slightly higher relevance for Leu and Val during the grower period. The concluded IAARBCAA was markedly lower than the IAARBCAA found in the literature (100:110:68:79). HPLC analysis showed no significant changes in the branched-chain α-keto acid content in the blood plasma between 3-12h after deprivation of feed. It was concluded that this timeframe is preferable for taking blood samples, if the branched-chain keto acids are to be analyzed. In Experiment 3, the Reference IAARBCAA (Lys:Leu:Ile:Val = 100:110:68:79) was compared to markedly lower BCAA-contents in a diet for broiler chickens (Lys:Leu:Ile:Val = 100:89:53:63 and 100:97:56:70 for starter and grower period, respectively). It was concluded that the lower IAARBCAA did not hamper the animals´ performance. Further research is believed to be necessary, on the one hand, for the the methodology. Besides a further optimization of N-balance-studies and growth assays a comparison of different models (e.g. N-utilization model and supplementation technique) for deriving AA-requirement/ IAAR-values within one experimental trial would be desirable. On the other hand, ongoing studies might not only take into account the content of the branched-chain α-keto acids but that of AA or uric acid in the blood plasma of broiler chickens as well. This might contribute to an even better understanding of the BCCAmetabolism and its effects on animals´ performance and health status.