ISSUE FOCUS FEED & ADDITIVE MAGAZINE November 2023 55 WHY SPEED MATTERS Digestion speed is important because the most efficient hydrolyzation and absorption occurs in the part of the small intestine that is called jejunum which is closer to the stomach and is more efficient in absorbing amino acids than the ileum which is further away from the stomach. The reason for this is that glucose is abundantly available as energy source for the intestinal cells in the jejunum that absorb the amino acids. This means that they can perform optimally and therefore, a greater proportion of amino acids pass into the bloodstream. Consequently, a smaller proportion needs to be oxidized to generate energy. Conversely, less glucose is available further down in the ileum. Therefore, intestinal cells located here will have to use a larger proportion of the amino acids as energy source, so that the functions of these intestinal cells can continue to be carried out (Van den Borne et al., 2007; Liu and Selle, 2017; He and Wu, 2022). Furthermore, insulin growth factor (IGF, which regulates the deposition of AA in tissues) reaches peak levels soon after feed consumption, which favors the deposition of AA during peak levels of IGF. So, the faster a protein is hydrolyzed and absorbed, the more of the protein will be used for protein deposition. We know now that fast absorbable protein ingredients improve nitrogen (N) retention and consequently growth and feed efficiency of the animals. The rate of protein hydrolysis, the consequent rate of AA absorption and the synchronization of absorption of AA from different dietary protein sources are especially important in young animals, due to their high AA requirements for the synthesis of muscle tissue and vital organs. Therefore, protein kinetics are more indicative of feed efficiency and protein deposition than the digestibility coefficient of the protein ingredient. Young animals have a very high protein requirement but underdeveloped digestive capacity They need a lot of protein to further develop their organs, while not fully equipped to extract all the required amino acids from the protein in the diet. FORMULATING DIETS CONSIDERING PROTEIN KINETICS In the current practice of feed formulation, digestible amino acids and net or metabolizable energy contents are used as fixed values of feed ingredients to optimize Apparent digestibility coefficients Protein digestion rate Ingredients Blood meal SBM HCP 0.568a 0.460ab 0.516b 0.564ab 0.717bcde 0.762abcd 0.761bcd 0.765bcd 0.124 a 0.066 b Proximal jejunum Distal jejunum Proximal ileum Distal ileum (min-1) Table 1. Apparent digestibility coefficients in different parts of the digestive tract. Adapted from Toghyani et al., 2020 6.6% of protein digested in 1 minute 12.4% of protein digested in 1 minute
RkJQdWJsaXNoZXIy MTUxNjkxNQ==