ARTICLE 78 FEED & ADDITIVE MAGAZINE April 2023 that the AA supply exactly matches the AA requirement. The requirements for AA in ideal protein are usually expressed relative to the requirement for Lys (i.e. Lys = 100%). The expression relative to Lys is very useful from a practical point of view. Lysine is typically the first-limiting AA in diets for pigs. Lysine has therefore received most of the nutritionists’ attention and considerable research has been carried out to describe the change in Lys requirements during growth, gestation, and lactation. If the requirements for the other AA are mostly driven by the requirement for protein synthesis, the requirements for these AA should be relatively constant (relative to Lys). This greatly simplifies practical pig nutrition because a nutritionist only has to have knowledge of the change in the Lys requirement over time and combine this with a constant ideal protein profile. The concept of ideal protein was first put into practice for pigs by the ARC. The AA requirement of growing pigs and gestating or lactation sows change rapidly during the production period, but diets are kept constant in most dose–response studies. AMINO ACID REQUIREMENTS FOR GROWING PIGS IN THE INRAPORC MODEL As indicated above, protein deposition is the main determinant for the AA requirements in growing pigs. These requirements, combined with feed intake, will determine the required AA content in the diet. However, both protein deposition and feed intake change during growth and the required AA content in the diet is determined by, roughly stated, the protein deposition curve and the feed intake curve. This information has to be provided by the user to obtain accurate estimates of the AA requirements. Because of the strong relationship between body protein and body water, there is also a strong relationship between body protein and body weight. A procedure is provided where the user can provide serial measurements of body weight and feed intake (with a minimum of 3 measurements for the growing-finishing period) from which the software will determine feed intake and protein deposition curves. The protein deposition curve is described by 3 model parameters: the initial protein mass (which is strongly related to the initial body weight), the average protein deposition over the growing period (related to the average daily gain) and a “precocity” parameter describing if the animal is early- or late-maturing. InraPorc provides an estimate of the AA requirements for an individual animal as indicated. This requirement is lower than the requirement of a population with the same average performance. InraPorc will give an indication for the requirement of a population of pigs, which is approximately 10% greater than the requirement of the average pig. One important progress in animal nutrition in recent years and thus also in broiler nutrition research has been the development of the concept of an "Ideal Protein". One basic idea of this concept is that birds need amino acids in a certain balance to ensure optimum performance. Any absorbed amino acid which is in relative excess compared to the first limiting amino acid will be oxidised and nitrogen will be excreted. Therefore, adjusting the dietary amino acid supply according to the “Ideal Protein Concept” helps to maximise nitrogen utilisation. One practical application resulting from this is the establishment of low protein diets allowing for the same animal performance if compared to unbalanced high protein diets. A second basic idea of this concept is that while the bird's requirement for essential amino acids may vary between various practical situation, the ratios between
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