Current knowledge about ideal protein for growing pigs

Abstract Text: Improving the efficiency of nitrogen use and maintaining performance can be achieved by reducing the crude protein content of diet while ensuring that amino acid requirements, defined as the minimum amino acid supply required to obtain a maximum response, are met. The use of synthetic amino acids and analogues allows formulating diets where 7 amino acids are co-limiting for performance (i.e., Lys, Met, Met+Cys, Thr, Trp, Val, and a 7^thamino acid). Knowledge of the requirements of these amino acids has been a limiting factor for the further reduction of protein content in the diet and thus for improving the efficiency of nitrogen utilization. Dose-response experiments are usually carried out to estimate the amino acid requirement. The experimental design, the mode of expressing the amino acid supply, the response criterion used and the statistical analysis method affect the amino acid requirement estimates. Very little experimental evidence exists for the requirements of amino acids such as Val, Ile, Leu, His, Phe, and Tyr. Our group has carried out an experimental research program to study the response of piglets to the supply of these amino acids. In addition, meta-analyses were used to analyze the existing body of literature. Based on current knowledge and expressed on a standardized ileal digestible basis relative to Lys, our recommended ideal amino acid profile for growing pigs is: 30% Met, 60% Met+Cys, 65% Thr, 22% Trp, 70% Val, 52% Ile, 101% Leu, 31% His, 54% Phe, and 40% Tyr. For the amino acids we have studied, these estimates include a safety margin because requirement estimates were obtained using a curvilinear-plateau model, ensuring that the requirement of most pigs in the population is met. A 10% deficiency relative to the requirement results in a growth reduction of 1.0, 9.3, 7.0, 3.8, 3.5, 3.2, and 0.6% for Trp, Val, Ile, Leu, His, Phe, and Tyr, respectively. The reduction in growth was mostly due to a reduction in feed intake. An excess supply of an amino acid can reduce the availability of other amino acids due to competition for catabolism and transport. For example, the use of blood cells (high in Val, Leu, His, and Phe) increases the Ile requirement while excess Leu aggravates the effect of a Val deficiency. Knowledge of the response of animals to the amino acid supply allows formulating diets with a precision protein profile that approaches that of ideal protein.

Keywords: amino acids ideal protein pigs