Formulating poultry diets based on their indigestible components

Since it started as an organized economic activity, poultry production has been undergoing an evolution toward the optimization of its feed formulation features. Notably, advances in the knowledge of birds' nutrient requirements have allowed recommendations that are increasingly closer to the needs of the birds. Over time, availability of nutrients and energy has been incorporated into those recommendations, especially to compensate for the variability in the digestibility of nutrients originating from variable feed ingredient sources. Instead of using the total energy and nutrient content, current tables of nutrient recommendations provide an estimate of the digestible fractions of the nutrients in ingredients. For instance, nonphytate P is preferred instead of total P to account for the unavailable phytate P, and digestible amino acids to account for the differences in digestibility of amino acids in different ingredients, whereas energy is usually expressed as a proportion that has been digested and metabolized (AME). With the increasing interest in the use of exogenous enzymes in poultry feeds, special attention is directed to the feed substrates such that an added enzyme can match it, forming an enzyme-substrate complex that will be followed by a chemical reaction within the gastrointestinal tract. As a consequence of a degradation reaction, nutrients released can be absorbed and metabolized. In general, nutritional data banks used in linear feed formulation software have limited data on the proportions of fractions of ingredients that are indigestible. Therefore, estimations of the presence of many substrates in the feeds, and therefore the benefits of adding exogenous enzymes, are frequently limited because of the scarcity of adequate information. The objective of this review paper is to provide insights into the use of expanded nutrient databanks to include all the molecules considered potentially indigestible for poultry such that the inclusion of exogenous enzymes allows the estimation of the values of the product originated by their hydrolysis.